Transcript Cells and Metabolism Big Idea Powerpoint

Cells and Metabolism Big
Ideas
L.O. 1.15 – The student is able to describe specific examples of
conserved core biological processes and features shared by all
domains or within one domain of life, and how these shared,
conserved core processes and features support the concept of
common ancestry for all living organisms.
Essential knowledge 2.A.1: All living
systems require constant input of
free energy.
a. Life requires a highly ordered system.
1. Order is maintained by constant free energy input into the system.
2. Loss of order or free energy flow results in death.
3. Increased disorder and entropy are offset by biological processes that
maintain or increase order.
b. Living systems do not violate the second law of thermodynamics,
which states that entropy increases over time.
1. Order is maintained by coupling cellular processes that increase entropy
(and so have negative changes in free energy) with those that decrease
entropy (and so have positive changes in free energy).
2. Energy input must exceed free energy lost to entropy to maintain order
and power cellular processes.
3. Energetically favorable exergonic reactions, such as ATP→ADP, that
have a negative change in free energy can be used to maintain or increase
order in a system by being coupled with reactions that have a positive free
energy change.
•
c. Energy-related pathways in biological systems are sequential and may be
entered at multiple points in the pathway. [See also 2.A.2]
• Krebs cycle
• Glycolysis
• Calvin cycle
• Fermentation
d. Organisms use free energy to maintain organization, grow and reproduce.
1. Organisms use various strategies to regulate body temperature and metabolism.
• Endothermy (the use of thermal energy generated bymetabolism to maintain
homeostatic body temperatures.
• Ectothermy (the use of external thermal energy to help regulate and maintain
body temperature)
• Elevated floral temperatures in some plant species
2. Reproduction and rearing of offspring require free energy beyond that used for
maintenance and growth. Different organisms use various reproductive strategies in
response to energy availability.
• Seasonal reproduction in animals and plants
• Life-history strategy (biennial plants, reproductive diapause)
3. There is a relationship between metabolic rate per unit body mass and the size of
multicellular organisms — generally, the smaller the organism, the higher the
metabolic rate.
4. Excess acquired free energy versus required free energy expenditure results in
energy storage or growth.
5. Insufficient acquired free energy versus required free energy expenditure results in
loss of mass and, ultimately, the death of an organism
e. Changes in free energy availability can result in changes in
population size.
f. Changes in free energy availability can result in disruptions to an
ecosystem.
• Change in the producer level can affect the number and size of
other trophic levels.
• Change in energy resources levels such as sunlight can affect the
number and size of the trophic levels.
Learning Objectives:
• LO 2.1 The student is able to explain how biological systems use
free energy based on empirical data that all organisms require
constant energy input to maintain organization, to grow and to
reproduce. [See SP 6.2]
• LO 2.2 The student is able to justify a scientific claim that free
energy is required for living systems to maintain organization, to
grow or to reproduce, but that multiple strategies exist in different
living systems. [See SP 6.1]
• LO 2.3 The student is able to predict how changes in free energy
availability affect organisms, populations and ecosystems. [See SP
6.4]
The Laws of Energy
Transformation
• Thermodynamics is the study of energy
transformations
• A isolated system, such as that approximated by
liquid in a thermos, is isolated from its
surroundings
• In an open system, energy and matter can be
transferred between the system and its
surroundings
• Organisms are open systems
© 2011 Pearson Education, Inc.
The First Law of
Thermodynamics
• According to the first law of thermodynamics,
the energy of the universe is constant
– Energy can be transferred and transformed,
but it cannot be created or destroyed
• The first law is also called the principle of
conservation of energy
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The Second Law of
Thermodynamics
• During every energy transfer or transformation,
some energy is unusable, and is often lost as
heat
• According to the second law of
thermodynamics
– Every energy transfer or transformation
increases the entropy (disorder) of the
universe
© 2011 Pearson Education, Inc.
Figure 8.3
Heat
Chemical
energy
(a) First law of thermodynamics
(b) Second law of thermodynamics
Free-Energy Change, G
• A living system’s free energy is energy that
can do work when temperature and pressure
are uniform, as in a living cell
• The free-energy change of a reaction tells us
whether or not the reaction occurs
spontaneously
© 2011 Pearson Education, Inc.
• The change in free energy (∆G) during a
process is related to the change in enthalpy, or
change in total energy (∆H), change in entropy
(∆S), and temperature in Kelvin (T)
∆G = ∆H – T∆S
• Only processes with a negative ∆G are
spontaneous
• Spontaneous processes can be harnessed to
perform work
© 2011 Pearson Education, Inc.
Free Energy, Stability, and
Equilibrium
• Free energy is a measure of a system’s
instability, its tendency to change to a more
stable state
• During a spontaneous change, free energy
decreases and the stability of a system
increases
• Equilibrium is a state of maximum stability
• A process is spontaneous and can perform
work only when it is moving toward equilibrium
© 2011 Pearson Education, Inc.
Figure 8.5
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy of the system
decreases (G  0)
• The system becomes more
stable
• The released free energy can
be harnessed to do work
• Less free energy (lower G)
• More stable
• Less work capacity
(a) Gravitational motion
(b) Diffusion
(c) Chemical reaction
Exergonic and Endergonic
Reactions in Metabolism
• An exergonic reaction proceeds with a net
release of free energy and is spontaneous
• An endergonic reaction absorbs free energy
from its surroundings and is nonspontaneous
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(a) Exergonic reaction: energy released, spontaneous
Reactants
Free energy
Amount of
energy
released
(G  0)
Energy
Products
Progress of the reaction
(b) Endergonic reaction: energy required, nonspontaneous
Products
Free energy
Figure 8.6
Amount of
energy
required
(G  0)
Energy
Reactants
Progress of the reaction
Equilibrium and Metabolism
• Reactions in a closed system eventually reach
equilibrium and then do no work
• Cells are not in equilibrium; they are open
systems experiencing a constant flow of
materials
• A defining feature of life is that metabolism is
never at equilibrium
• A catabolic pathway in a cell releases free energy
in a series of reactions
• Closed and open hydroelectric systems can
serve as analogies
© 2011 Pearson Education, Inc.
Figure 8.7
G  0
G  0
(a) An isolated hydroelectric system
(b) An open hydroelectric system
G  0
G  0
G  0
G  0
(c) A multistep open hydroelectric system
Concept 8.3: ATP powers cellular
work by coupling exergonic
reactions to endergonic reactions
• A cell does three main kinds of work
– Chemical
– Transport
– Mechanical
• To do work, cells manage energy resources by
energy coupling, the use of an exergonic
process to drive an endergonic one
• Most energy coupling in cells is mediated by ATP
© 2011 Pearson Education, Inc.
The Structure and Hydrolysis of
ATP
• ATP (adenosine triphosphate) is the cell’s
energy shuttle
• ATP is composed of ribose (a sugar), adenine
(a nitrogenous base), and three phosphate
groups
© 2011 Pearson Education, Inc.
Figure 8.8
Adenine
Phosphate groups
Ribose
(a) The structure of ATP
Adenosine triphosphate (ATP)
Energy
Inorganic
phosphate
Adenosine diphosphate (ADP)
(b) The hydrolysis of ATP
How the Hydrolysis of ATP
Performs Work
• The three types of cellular work (mechanical,
transport, and chemical) are powered by the
hydrolysis of ATP
• In the cell, the energy from the exergonic
reaction of ATP hydrolysis can be used to
drive an endergonic reaction
• Overall, the coupled reactions are exergonic
© 2011 Pearson Education, Inc.
Figure 8.9
(a) Glutamic acid
conversion
to glutamine
NH3
Glutamic
acid
(b) Conversion
reaction
coupled
with ATP
hydrolysis
NH2
Glu
Glu
GGlu = +3.4 kcal/mol
Glutamine
Ammonia
NH3
P
1
Glu
ATP
Glu
2
ADP
Glu
Phosphorylated
intermediate
Glutamic
acid
NH2
Glutamine
GGlu = +3.4 kcal/mol
(c) Free-energy
change for
coupled
reaction
NH3
Glu
GGlu = +3.4 kcal/mol
+ GATP = 7.3 kcal/mol
Net G = 3.9 kcal/mol
ATP
NH2
Glu
GATP = 7.3 kcal/mol
ADP
Pi
ADP
Pi
• ATP drives endergonic reactions by
phosphorylation, transferring a phosphate
group to some other molecule, such as a
reactant
• The recipient molecule is now called a
phosphorylated intermediate
© 2011 Pearson Education, Inc.
Figure 8.10
Transport protein
Solute
ATP
ADP
P
Pi
Pi
Solute transported
(a) Transport work: ATP phosphorylates transport proteins.
Cytoskeletal track
Vesicle
ATP
ADP
ATP
Motor protein
Protein and
vesicle moved
(b) Mechanical work: ATP binds noncovalently to motor
proteins and then is hydrolyzed.
Pi
The Regeneration of ATP
• ATP is a renewable resource that is
regenerated by addition of a phosphate
group to adenosine diphosphate (ADP)
• The energy to phosphorylate ADP comes
from catabolic reactions in the cell
• The ATP cycle is a revolving door through
which energy passes during its transfer from
catabolic to anabolic pathways
© 2011 Pearson Education, Inc.
Free Energy Equations and
Diagrams
Delta G? Activation
energy?
Essential knowledge 2.A.2: Organisms capture
and store free energy for use in biological
processes.
a. Autotrophs capture free energy from physical sources in the
environment.
1. Photosynthetic organisms capture free energy present in
sunlight.
2. Chemosynthetic organisms capture free energy from small
inorganic molecules present in their environment, and this process
can occur in the absence of oxygen.
b. Heterotrophs capture free energy present in carbon compounds
produced by other organisms.
1. Heterotrophs may metabolize carbohydrates, lipids and
proteins by hydrolysis as sources of free energy.
2. Fermentation produces organic molecules, including alcohol
and lactic acid, and it occurs in the absence of oxygen.
c. Different energy-capturing processes use different types of electron
acceptors.
• NADP+ in photosynthesis
• Oxygen in cellular respiration
d. The light-dependent reactions of photosynthesis in eukaryotes involve
a series of coordinated reaction pathways that capture free energy
present in light to yield ATP and NADPH, which power the production
of organic molecules.
1. During photosynthesis, chlorophylls absorb free energy from light,
boosting electrons to a higher energy level in Photosystems I and II.
2. Photosystems I and II are embedded in the internal membranes of
chloroplasts (thylakoids) and are connected by the transfer of higher free
energy electrons through an electron transport chain (ETC). [See also
4.A.2]
3. When electrons are transferred between molecules in a sequence
of reactions as they pass through the ETC, an electrochemical gradient of
hydrogen ions (protons) across the thykaloid membrane is established.
4. The formation of the proton gradient is a separate process, but it is
linked to the synthesis of ATP from ADP and inorganic phosphate via ATP
synthase.
5. The energy captured in the light reactions as ATP and NADPH
powers the production of carbohydrates from carbon dioxide in the Calvin
cycle, which occurs in the stroma of the chloroplast.
e. Photosynthesis first evolved in prokaryotic organisms; scientific
evidence supports that prokaryotic (bacterial) photosynthesis was
responsible for the production of an oxygenated atmosphere;
prokaryotic photosynthetic pathways were the foundation of
eukaryotic photosynthesis.
f. Cellular respiration in eukaryotes involves a series of coordinated
enzyme-catalyzed reactions that harvest free energy from simple
carbohydrates.
1. Glycolysis rearranges the bonds in glucose molecules, releasing
free energy to form ATP from ADP and inorganic phosphate, and resulting in
the production of pyruvate.
2. Pyruvate is transported from the cytoplasm to the mitochondrion,
where further oxidation occurs. [See also 4.A.2]
3. In the Krebs cycle, carbon dioxide is released from organic
intermediates ATP is synthesized from ADP and inorganic phosphate via
substrate level phosphorylation and electrons are captured by coenzymes.
4. Electrons that are extracted in the series of Krebs cycle reactions
are carried by NADH and FADH2 to the electron transport chain.
g. The electron transport chain captures free energy from electrons in a
series of coupled reactions that establish an electrochemical gradient
across membranes.
1. Electron transport chain reactions occur in chloroplasts
(photosynthesis), mitochondria (cellular respiration) and prokaryotic plasma
membranes.
2. In cellular respiration, electrons delivered by NADH and FADH2 are
passed to a series of electron acceptors as they move toward the terminal
electron acceptor, oxygen. In photosynthesis, the terminal electron acceptor
is NADP+.
3. The passage of electrons is accompanied by the formation of a
proton gradient across the inner mitochondrial membrane or the thylakoid
membrane of chloroplasts, with the membrane(s) separating a region of
high proton concentration from a region of low proton concentration. In
prokaryotes, the passage of electrons is accompanied by the outward
movement of protons across the plasma membrane.
4. The flow of protons back through membrane-bound ATP synthase
by chemiosmosis generates ATP from ADP and inorganic phosphate.
5. In cellular respiration, decoupling oxidative phosphorylation from
electron transport is involved in thermoregulation.
h. Free energy becomes available for metabolism by the conversion of
ATP→ADP, which is coupled to many steps in metabolic pathways.
Learning Objectives:
LO 2.4 The student is able to use representations
to pose scientific questions about what
mechanisms and structural features allow
organisms to capture, store and use free energy.
[See SP 1.4, 3.1]
LO 2.5 The student is able to construct
explanations of the mechanisms and structural
features of cells that allow organisms to capture,
store or use free energy. [See SP 6.2]
Light
energy
Figure 9.2
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2  H2O
Cellular respiration
in mitochondria
ATP
Heat
energy
Organic
 O2
molecules
ATP powers
most cellular work
Catabolic pathways yield energy
by oxidizing organic fuels to
produce ATP
• The breakdown of organic molecules is
exergonic
• Fermentation is a partial degradation of
sugars that occurs without O2
• Aerobic respiration consumes organic
molecules and O2 and yields ATP
• Anaerobic respiration is similar to aerobic
respiration but consumes compounds
other than O2
© 2011 Pearson Education, Inc.
• Cellular respiration includes both aerobic
and anaerobic respiration but is often used
to refer to aerobic respiration
• Although carbohydrates, fats, and proteins
are all consumed as fuel, it is helpful to
trace cellular respiration with the sugar
glucose
• C6H12O6 + 6 O2  6 CO2 + 6 H2O +
Energy (ATP + heat)
© 2011 Pearson Education, Inc.
The Principle of Redox
• Chemical reactions that transfer electrons
between reactants are called oxidationreduction reactions, or redox reactions
• In oxidation, a substance loses electrons,
or is oxidized
• In reduction, a substance gains electrons,
becomes oxidized
or is reduced (the
amount
(loses
electron)of positive
charge is reduced)
becomes reduced
(gains electron)
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Oxidation of Organic Fuel
Molecules During Cellular
Respiration
• During cellular respiration, the fuel (such
as glucose) is oxidized, and O2 is reduced
becomes oxidized
becomes reduced
© 2011 Pearson Education, Inc.
Stepwise Energy Harvest via
NAD+ and the Electron
Transport Chain
• In cellular respiration, glucose and other
organic molecules are broken down in a
series of steps
• Electrons from organic compounds are
usually first transferred to NAD+, a
coenzyme
• As an electron acceptor, NAD+ functions
as an oxidizing agent during cellular
respiration
• Each NADH (the reduced form of NAD+)
© 2011 Pearson Education, Inc.
Figure 9.4
NAD
NADH
Dehydrogenase
Reduction of NAD
(from food)
Oxidation of NADH
Nicotinamide
(oxidized form)
Nicotinamide
(reduced form)
Dehydrogenase
• NADH passes the electrons to the electron
transport chain
• Unlike an uncontrolled reaction, the
electron transport chain passes electrons
in a series of steps instead of one
explosive reaction
• O2 pulls electrons down the chain in an
energy-yielding tumble
• The energy yielded is used to regenerate
ATP
© 2011 Pearson Education, Inc.
H2  1/2 O2
Figure 9.5

2H
1/
Explosive
release of
heat and light
energy
Free energy, G
Free energy, G
(from food via NADH)
Controlled
release of
+

2H  2e
energy for
synthesis of
ATP
O2
ATP
ATP
ATP
2 e
2
1/
H+
H2O
(a) Uncontrolled reaction
2
H2O
(b) Cellular respiration
2
O2
NADH from glycolysis –
1.5 ATP vs. 2.5 ATP per
NADH depending on
which shuttle working
Electron shuttles
span membrane
2 NADH
Glycolysis
2 Pyruvate
Glucose
Moving into matrix – on your picture, point
to matrix, cristae, inner mitochondrial
membrane, and intermembrane space
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
CYTOSOL
6 NADH
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
4. Electrons that are extracted in the series of Krebs cycle reactions are
carried by NADH and FADH2 to the electron transport chain.
Electron shuttles
span membrane
2 NADH
Glycolysis
2 Pyruvate
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
6 NADH
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
CYTOSOL
Now moving to the inner mitochondrial membrane
g. The electron transport chain captures
free energy from electrons in a series
of coupled reactions that establish an
electrochemical gradient across
membranes.
1. Electron transport chain reactions
occur in chloroplasts (photosynthesis),
mitochondria (cellular respiration) and
prokaryotic plasma membranes.
Figure 9.13
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
2. In cellular
respiration,
electrons
delivered by
NADH and
FADH2 are
passed to a
series of
electron
acceptors as
they move
toward
the
The
terminal
electrons
electronby
carried
acceptor,
FADH2
oxygen.
have lower
free energy
NADH
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
• 3. The passage of electrons is accompanied by
the formation of a proton gradient across the
inner mitochondrial membrane or the thylakoid
membrane of chloroplasts, with the
membrane(s) separating a region of high proton
concentration from a region of low proton
concentration. In prokaryotes, the passage of
electrons is accompanied by the outward
movement of protons across the plasma
membrane.
Figure 9.15
H
H

H
Protein
complex
of electron
carriers
Cyt c
Q
I
IV
III
II
FADH2 FAD
NADH
H
2 H + 1/2O2
ATP
synthase
H2O
NAD
ADP  P i
(carrying electrons
from food)
ATP
H
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis
Figure 9.14
4. The flow of protons back
through membrane-bound ATP
synthase by chemiosmosis
generates ATP from ADP and
inorganic phosphate.
• ATP synthase uses the
exergonic flow of H+ to
drive phosphorylation of
ATP
• This is an example of
chemiosmosis, the use of
energy in a H+ gradient to
drive cellular work
• The H+ gradient is referred
to as a proton-motive
force, emphasizing its
capacity to do work
INTERMEMBRANE SPACE
H
Stator
Rotor
Internal
rod
Catalytic
knob
ADP
+
Pi
ATP
MITOCHONDRIAL MATRIX
Figure 9.16
Electron shuttles
span membrane
2 NADH
Glycolysis
2 Pyruvate
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
CYTOSOL
6 NADH
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
5. In cellular respiration, decoupling
oxidative phosphorylation from electron
transport is involved in thermoregulation.
• Used by hibernating mammals
• Brown fat, high in mitochondria, with ETC
uncoupling protein
– Protein is activated during hibernation
– Allows protons to flow back down their gradient
without making ATP (uncoupled)
– Ongoing oxidation of stored fuel generates heat to
keep body temp warmer than environment
– If ATP were made, would build up to high levels that
would shut down the cell respiration pathways
Temp regulation
Fermentation produces organic molecules,
including alcohol and lactic acid, and it
occurs in the absence of oxygen.
See Ch. 9 slide 78 Animation
• In alcohol fermentation, pyruvate is
converted to ethanol in two steps.
– First, pyruvate is converted to a two-carbon
compound, acetaldehyde by the removal of
CO2.
– Second, acetaldehyde is reduced by NADH to
ethanol.
– Alcohol fermentation
by yeast is used in
brewing and
winemaking.
Fig. 9.17a
• During lactic acid fermentation, pyruvate
is reduced directly by NADH to form lactate
(ionized form of lactic acid).
– Lactic acid fermentation by some fungi and
bacteria is used to make cheese and yogurt.
– Muscle cells switch from aerobic respiration to
lactic acid fermentation to generate ATP when
O2 is scarce.
• The waste product,
lactate, may cause
muscle fatigue, but
ultimately it is
converted back to
pyruvate in the liver.
Fig. 9.17b
• Some organisms (facultative anaerobes),
including yeast and many bacteria, can survive
using either fermentation or respiration.
• At a cellular level, human
muscle cells can behave
as facultative anaerobes,
but nerve cells cannot.
• For facultative anaerobes,
pyruvate is a fork in the
metabolic road that leads
to two alternative routes.
Fig. 9.18
The Evolutionary Significance of
Glycolysis
• Ancient prokaryotes are thought to have used
glycolysis long before there was oxygen in the
atmosphere
• Very little O2 was available in the atmosphere
until about 2.7 billion years ago, so early
prokaryotes likely used only glycolysis to
generate ATP
• Glycolysis is a very ancient process
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• Control of catabolism
is based mainly on
regulating the activity
of enzymes at
strategic points in the
catabolic pathway.
• One strategic point
occurs in the third
step of glycolysis,
catalyzed by
phosphofructokinase.
Fig. 9.20
• Carbohydrates,
fats, and proteins
can all be
catabolized
through the same
pathways.
Fig. 9.19
Chloroplasts: The Sites of
Photosynthesis in Plants
• Leaves are the major locations of
photosynthesis
• Their green color is from chlorophyll, the
green pigment within chloroplasts
• Chloroplasts are found mainly in cells of the
mesophyll, the interior tissue of the leaf
• Each mesophyll cell contains 30–40
chloroplasts
© 2011 Pearson
• CO2 enters and O2 exits the leaf through
microscopic pores called stomata
• The chlorophyll is in the membranes of
thylakoids (connected sacs in the chloroplast);
thylakoids may be stacked in columns called
grana
• Chloroplasts also contain stroma, a dense
interior fluid
© 2011 Pearson
Figure 10.4
Leaf cross section
Chloroplasts Vein
Mesophyll
Stomata
Chloroplast
Thylakoid
Stroma Granum Thylakoid
space
Let’s look
at model
1 m
CO2 O2
Mesophyll
cell
Outer
membrane
Intermembrane
space
Inner
membrane
20 m
Photosynthesis as a Redox
Process
• Photosynthesis reverses the direction of electron
flow compared to respiration
• Photosynthesis is a redox process in which H2O
is oxidized and CO2 is reduced
• Photosynthesis is an endergonic process; the
energy boost is provided by light
becomes reduced
Energy  6 CO2  6 H2O
C6 H12 O6  6 O2
becomes oxidized
© 2011 Pearson
The Two Stages of
Photosynthesis: A Preview
• Photosynthesis consists of the light
reactions (the photo part) and Calvin cycle
(the synthesis part)
• The light reactions (in the thylakoids)
–
–
–
–
Split H2O
Release O2
Reduce NADP+ to NADPH
Generate ATP from ADP by
photophosphorylation
© 2011 Pearson
• The Calvin cycle (in the stroma) forms sugar
from CO2, using ATP and NADPH
• The Calvin cycle begins with carbon fixation,
incorporating CO2 into organic molecules
© 2011 Pearson
Figure 10.6-4
CO2
H2O
Light
NADP
ADP
+ Pi
Light
Reactions
Calvin
Cycle
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
• While light travels as a wave, many of its
properties are those of a discrete particle, the
photon.
– Photons are not tangible objects, but they do have fixed
quantities of energy and amount depends on wavelength.
(a) Absorption
spectra
(b) Action spectrum
Absorption of light by
chloroplast pigments
RESULTS
Rate of photosynthesis
(measured by O2 release)
Figure 10.10
Chlorophyll a
Chlorophyll b
Carotenoids
400
500
600
Wavelength of light (nm)
400
500
600
700
700
Aerobic bacteria
Filament
of alga
(c) Engelmann’s
experiment
400
500
600
700
• Chlorophyll a is the main photosynthetic pigment
• Accessory pigments, such as chlorophyll b,
broaden the spectrum used for photosynthesis
• Accessory pigments called carotenoids absorb
excessive light that would damage chlorophyll
© 2011 Pearson
• Excited electrons are unstable.
• Generally, they drop to their ground state in
a billionth of a second, releasing heat
energy.
• Some pigments, including chlorophyll,
release a photon of light, in a process
called fluorescence, as well as heat.
Fig. 10.10
Fig. 10.9
Figure 10.18
STROMA
(low H concentration)
Photosystem II
4 H+
Light
Cytochrome
complex
Photosystem I
Light
NADP
reductase
3
NADP + H
Fd
Pq
H2O
NADPH
Pc
2
1
THYLAKOID SPACE
(high H concentration)
1/
2
O2
+2 H+
4 H+
To
Calvin
Cycle
Thylakoid
membrane
STROMA
(low H concentration)
ATP
synthase
ADP
+
Pi
ATP
H+
A Photosystem: A Reaction-Center
Complex Associated with LightHarvesting Complexes
• A photosystem consists of a reaction-center
complex (a type of protein complex) surrounded
by light-harvesting complexes
• The light-harvesting complexes (pigment
molecules bound to proteins) transfer the energy
of photons to the reaction center
© 2011 Pearson
Figure 10.13
Thylakoid membrane
Lightharvesting
complexes
Reactioncenter
complex
STROMA
Primary
electron
acceptor
e
Transfer
of energy
Pigment
Special pair of
molecules
chlorophyll a
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
(a) How a photosystem harvests light
Thylakoid membrane
Photosystem
Photon
Chlorophyll
Protein
subunits
STROMA
THYLAKOID
SPACE
(b) Structure of photosystem II
Each photosystem consists of chlorophylls, accessory pigments, and
proteins. The black arrows represent photons being passed like a wave to
reaction center chlorophylls that actually donate their electrons.
Figure 10.14-5
Linear Electron Flow
4
Primary
acceptor
2
H
+
1/ O
2
2
H2O
e
2
Primary
acceptor
e
Pq
7
Fd
e 
e
Cytochrome
complex
8
NADP
reductase
3
Pc
e
e
P700
5
P680
Light
1 Light
6
ATP
Pigment
molecules
Photosystem II
(PS II)
Photosystem I
(PS I)
NADP
+ H
NADPH
Figure 10.15
e
e
e
e
Mill
makes
ATP
e
NADPH
e
e
ATP
Photosystem II
Photosystem I
Let’s watch animation of Phase I
• http://www.mhhe.com/biosci/genbio/biolink
/j_explorations/ch09expl.htm
A Comparison of Chemiosmosis
in Chloroplasts and Mitochondria
• Chloroplasts and mitochondria generate ATP by
chemiosmosis, but use different sources of
energy
• Mitochondria transfer chemical energy from
food to ATP; chloroplasts transform light energy
into the chemical energy of ATP
• Spatial organization of chemiosmosis differs
between chloroplasts and mitochondria but also
shows similarities
© 2011 Pearson
• In mitochondria, protons are pumped to the
intermembrane space and drive ATP synthesis
as they diffuse back into the mitochondrial matrix
• In chloroplasts, protons are pumped into the
thylakoid space and drive ATP synthesis as they
diffuse back into the stroma
© 2011 Pearson
Figure 10.17
Chloroplast
Mitochondrion
CHLOROPLAST
STRUCTURE
MITOCHONDRION
STRUCTURE
H
Intermembrane
space
Inner
membrane
Diffusion
Electron
transport
chain
Thylakoid
space
Thylakoid
membrane
ATP
synthase
Matrix
Stroma
ADP  P i
Key
[H ]
Higher
Lower [H ]
H
ATP
• ATP and NADPH are produced on the side
facing the stroma, where the Calvin cycle takes
place
• In summary, light reactions generate ATP and
increase the potential energy of electrons by
moving them from H2O to NADPH
© 2011 Pearson
Figure 10.19-3
Input
(Entering one
CO2 at a time)
3
Calvin Cycle
Phase 1: Carbon fixation
Rubisco
3 P
Short-lived
intermediate
P
6
P
3-Phosphoglycerate
P
3P
Ribulose bisphosphate
(RuBP)
6
ATP
6 ADP
3 ADP
3
Calvin
Cycle
6 P
P
1,3-Bisphosphoglycerate
ATP
6 NADPH
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
6 NADP
6 Pi
P
5
G3P
For every one net G3P, requires 9
ATP and 6 NADPH from the
light reaction.
6
P
Glyceraldehyde 3-phosphate
(G3P)
1
P
G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
Cyclic Electron Flow
• Cyclic electron flow uses only photosystem I
and produces ATP, but not NADPH
• No oxygen is released
• Cyclic electron flow generates surplus ATP,
satisfying the higher demand in the Calvin cycle
© 2011 Pearson
Figure 10.16
Primary
acceptor
Primary
acceptor
Fd
Fd
Pq
NADP
reductase
Cytochrome
complex
NADPH
Pc
Photosystem I
Photosystem II
ATP
NADP
+ H
Photosynthesis is the biosphere’s
metabolic foundation
• In photosynthesis, the energy that enters the
chloroplasts as sunlight becomes stored as
chemical energy in organic compounds.
- About 50% of the
organic material made
is consumed as fuel
for cellular respiration
in plant mitochondria.
– Rest is stored or
used to build other
organic compounds.
• On a global scale, photosynthesis is the
most important process to the welfare of life
on Earth.
– Each year photosynthesis synthesizes 160
billion metric tons of carbohydrate per year.
Essential knowledge 2.B.1: Cell membranes
are selectively permeable due to their
structure.
a. Cell membranes separate the internal environment of the cell from the external
environment.
b. Selective permeability is a direct consequence of membrane structure, as
described by the fluid mosaic model. [See also 4.A.1]
1. Cell membranes consist of a structural framework of phospholipid
molecules, embedded proteins, cholesterol, glycoproteins and glycolipids.
2. Phospholipids give the membrane both hydrophilic and hydrophobic
properties. The hydrophilic phosphate portions of the phospholipids are oriented
toward the aqueous external or internal environments, while the hydrophobic fatty
acid portions face each other within the interior of the membrane itself.
3. Embedded proteins can be hydrophilic, with charged and polar side groups,
or hydrophobic, with nonpolar side groups.
4. Small, uncharged polar molecules and small nonpolar molecules, such as
N2, freely pass across the membrane. Hydrophilic substances such as large polar
molecules and ions move across the membrane through embedded channel and
transport proteins. Water moves across membranes and through channel proteins
called aquaporins.
c. Cell walls provide a structural boundary, as well as a
permeability barrier for some substances to the internal
environments.
1. Plant cell walls are made of cellulose and are
external to the cell membrane.
2. Other examples are cells walls of prokaryotes and
fungi.
Learning Objectives:
LO 2.10 The student is able to use representations and
models to pose scientific questions about the properties
of cell membranes and selective permeability based on
molecular structure. [See SP 1.4, 3.1]
LO 2.11 The student is able to construct models that
connect the movement of molecules across membranes
with membrane structure and function. [See SP 1.1, 7.1,
7.2]
Essential knowledge 2.B.2: Growth and dynamic
homeostasis are maintained by the constant movement
of molecules across membranes.
a. Passive transport does not require the input of metabolic energy; the net
movement of molecules is from high concentration to low concentration.
1. Passive transport plays a primary role in the import of resources
and the export of wastes.
2. Membrane proteins play a role in facilitated diffusion of charged and
polar molecules through a membrane.
• Glucose transport
• Na+/K+ transport
3. External environments can be hypotonic, hypertonic or isotonic to
internal environments of cells.
b. Active transport requires free energy to move molecules from regions of low
concentration to regions of high concentration.
1. Active transport is a process where free energy (often provided by
ATP) is used by proteins embedded in the membrane to “move” molecules
and/or ions across the membrane and to establish and maintain
concentration gradients.
2. Membrane proteins are necessary for active transport.
• c. The processes of endocytosis and exocytosis move
large molecules from the external environment to the
internal environment and vice versa, respectively.
1. In exocytosis, internal vesicles fuse with the
plasma membrane to secrete large macromolecules out
of the cell.
2. In endocytosis, the cell takes in macromolecules
and particulate matter by forming new vesicles derived
from the plasma membrane.
Learning Objective
LO 2.12 The student is able to use representations and
models to analyze situations or solve problems
qualitatively and quantitatively to investigate whether
dynamic homeostasis is maintained by the active
movement of molecules across membranes. [See SP1.4]
Concept 7.1: Cellular
membranes are fluid mosaics of
lipids and proteins
• Phospholipids are the most abundant lipid in the
plasma membrane
• Phospholipids are amphipathic molecules,
containing hydrophobic and hydrophilic regions
• The fluid mosaic model states that a
membrane is a fluid structure with a “mosaic” of
various proteins embedded in it
© 2011 Pearson Education, Inc.
Figure 7.2
Hydrophilic
head
WATER
Hydrophobic
tail
WATER
Figure 7.3
Phospholipid
bilayer
Hydrophobic regions
of protein
Hydrophilic
regions of protein
Figure 7.5
Fibers of extracellular matrix (ECM)
Glycoprotein
Carbohydrate
Glycolipid
EXTRACELLULAR
SIDE OF
MEMBRANE
Cholesterol
Microfilaments
of cytoskeleton
Peripheral
proteins
Integral
protein
CYTOPLASMIC SIDE
OF MEMBRANE
Figure 7.6
Lateral movement occurs
107 times per second.
Flip-flopping across the membrane
is rare ( once per month).
Figure 7.7
RESULTS
Membrane proteins
Mouse cell
Mixed proteins
after 1 hour
Human cell
Hybrid cell
• As temperatures cool, membranes switch
from a fluid state to a solid state
• The temperature at which a membrane
solidifies depends on the types of lipids
• Membranes rich in unsaturated fatty acids
are more fluid than those rich in saturated
fatty acids
• Membranes must be fluid to work properly;
they are usually about as fluid as salad oil
© 2011 Pearson Education, Inc.
• The steroid cholesterol has different effects on
membrane fluidity at different temperatures
• At warm temperatures (such as 37°C),
cholesterol restrains movement of
phospholipids
• At cool temperatures, it maintains fluidity by
preventing tight packing
© 2011 Pearson Education, Inc.
Figure 7.8
Fluid
Viscous
Unsaturated hydrocarbonSaturated hydrocarbon tails
tails
(a) Unsaturated versus saturated hydrocarbon tails
(b) Cholesterol within the animal
cell membrane
Cholesterol
Evolution of Differences in
Membrane Lipid Composition
• Variations in lipid composition of cell
membranes of many species appear to be
adaptations to specific environmental
conditions
• Ability to change the lipid compositions in
response to temperature changes has evolved
in organisms that live where temperatures vary
© 2011 Pearson Education, Inc.
• Peripheral proteins are bound to the surface
of the membrane
• Integral proteins penetrate the hydrophobic
core
• Integral proteins that span the membrane are
called transmembrane proteins
• The hydrophobic regions of an integral protein
consist of one or more stretches of nonpolar
amino acids, often coiled into alpha helices
© 2011 Pearson Education, Inc.
Figure 7.9
EXTRACELLULAR
SIDE
N-terminus
 helix
C-terminus
CYTOPLASMIC
SIDE
Figure 7.10
Signaling molecule
Enzymes
ATP
(a) Transport
Receptor
Signal transduction
(b) Enzymatic activity
(c) Signal transduction
Glycoprotein
(d) Cell-cell recognition (e) Intercellular joining (f) Attachment to
the cytoskeleton
and extracellular
matrix (ECM)
The Role of Membrane
Carbohydrates in Cell-Cell
Recognition
• Cells recognize each other by binding to surface
molecules, often containing carbohydrates, on
the extracellular surface of the plasma
membrane
• Membrane carbohydrates may be covalently
bonded to lipids (forming glycolipids) or more
commonly to proteins (forming glycoproteins)
• Carbohydrates on the external side of the
plasma membrane vary among species,
individuals, and even cell types in an individual
© 2011 Pearson Education, Inc.
Figure 7.11
HIV
Receptor
(CD4)
Co-receptor
(CCR5)
HIV can infect a cell that
has CCR5 on its surface,
as in most people.
Receptor (CD4)
but no CCR5
Plasma
membrane
HIV cannot infect a cell lacking
CCR5 on its surface, as in
resistant individuals.
Concept 7.2: Membrane
structure results in selective
permeability
• A cell must exchange materials with its
surroundings, a process controlled by the
plasma membrane
• Plasma membranes are selectively permeable,
regulating the cell’s molecular traffic
• Hydrophobic (nonpolar) molecules, such as
hydrocarbons, can dissolve in the lipid bilayer
and pass through the membrane rapidly
• Polar molecules, such as sugars, do not cross
the membrane easily
© 2011 Pearson Education, Inc.
Transport Proteins
• Transport proteins allow passage of
hydrophilic substances across the membrane
• Some transport proteins, called channel
proteins, have a hydrophilic channel that
certain molecules or ions can use as a tunnel
• Channel proteins called aquaporins facilitate
the passage of water
• Other transport proteins, called carrier
proteins, bind to molecules and change shape
to shuttle them across the membrane
• A transport protein is specific for the substance
it moves
© 2011 Pearson Education, Inc.
Figure 7.17
EXTRACELLULAR
FLUID
(a) A channel
protein
Channel protein
Solute
CYTOPLASM
Carrier protein
(b) A carrier protein
Solute
Facilitated Diffusion: Passive
Transport Aided by Proteins
• In facilitated diffusion, transport proteins speed
the passive movement of molecules across the
plasma membrane
• Channel proteins provide corridors that allow a
specific molecule or ion to cross the membrane
• Channel proteins include
– Aquaporins, for facilitated diffusion of water
– Ion channels that open or close in response
to a stimulus (gated channels)
© 2011 Pearson Education, Inc.
Concept 7.4: Active transport
uses energy to move solutes
against their gradients
• Facilitated diffusion is still passive because the
solute moves down its concentration gradient,
and the transport requires no energy
• Some transport proteins, however, can move
solutes against their concentration gradients
© 2011 Pearson Education, Inc.
The Need for Energy in Active
Transport
• Active transport moves substances against
their concentration gradients
• Active transport requires energy, usually in the
form of ATP
• Active transport is performed by specific
proteins embedded in the membranes
© 2011 Pearson Education, Inc.
Animation: Active Transport
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
• Active transport allows cells to maintain
concentration gradients that differ from their
surroundings
• The sodium-potassium pump is one type of
active transport system
© 2011 Pearson Education, Inc.
Figure 7.18-6
EXTRACELLULAR [Na] high
FLUID
[K] low
Na
Na
Na
Na
Na
Na
Na
Na
CYTOPLASM Na
1
[Na] low
[K] high
P
ADP
2
ATP
P
3
K
K
K
6
K
K
K
5
4
P
Pi
Figure 7.19
Diffusion
Passive transport
Facilitated diffusion
Active transport
ATP
How Ion Pumps Maintain
Membrane Potential
• Membrane potential is the voltage difference
across a membrane
• Voltage is created by differences in the
distribution of positive and negative ions across
a membrane
© 2011 Pearson Education, Inc.
• Two combined forces, collectively called the
electrochemical gradient, drive the diffusion
of ions across a membrane
– A chemical force (the ion’s concentration
gradient)
– An electrical force (the effect of the membrane
potential on the ion’s movement)
© 2011 Pearson Education, Inc.
• An electrogenic pump is a transport protein
that generates voltage across a membrane
• The sodium-potassium pump is the major
electrogenic pump of animal cells
• The main electrogenic pump of plants, fungi,
and bacteria is a proton pump
• Electrogenic pumps help store energy that can
be used for cellular work
© 2011 Pearson Education, Inc.
Figure 7.20
ATP



Proton pump
H

CYTOPLASM


EXTRACELLULAR
FLUID

H
H
H


H
H
Cotransport: Coupled
Transport by a Membrane
Protein
• Cotransport occurs when active transport of a
solute indirectly drives transport of other
solutes
• Plants commonly use the gradient of hydrogen
ions generated by proton pumps to drive
active transport of nutrients into the cell
© 2011 Pearson Education, Inc.
Figure 7.21
ATP

H
H

H
Proton pump
H

H


H
H

H
Sucrose-H
cotransporter
Sucrose

Diffusion of H

Sucrose
Concept 7.5: Bulk transport
across the plasma membrane
occurs by exocytosis and
endocytosis
• Small molecules and water enter or leave the
cell through the lipid bilayer or via transport
proteins
• Large molecules, such as polysaccharides and
proteins, cross the membrane in bulk via
vesicles
• Bulk transport requires energy
© 2011 Pearson Education, Inc.
Animation: Exocytosis and Endocytosis
Introduction
© 2011 Pearson Education, Inc.
Right-click slide / select “Play”
Exocytosis
• In exocytosis, transport vesicles migrate to the
membrane, fuse with it, and release their
contents
• Many secretory cells use exocytosis to
export their products
© 2011 Pearson Education, Inc.
Animation:
Exocytosis
© 2011 Pearson Education, Inc.
Right-click slide / select “Play”
Endocytosis
• In endocytosis, the cell takes in macromolecules
by forming vesicles from the plasma membrane
• Endocytosis is a reversal of exocytosis, involving
different proteins
• There are three types of endocytosis
– Phagocytosis (“cellular eating”)
– Pinocytosis (“cellular drinking”)
– Receptor-mediated endocytosis
© 2011 Pearson Education, Inc.
In phagocytosis
a cell engulfs a
particle in a
vacuole
The vacuole
fuses with a
lysosome to
digest the particle
Animation:
Phagocytosis
© 2011 Pearson Education, Inc.
Right-click slide / select “Play”
• In pinocytosis,
molecules are
taken up when
extracellular
fluid is “gulped”
into tiny vesicles
Animation:
Pinocytosis
© 2011 Pearson Education, Inc.
Right-click slide / select “Play”
• In receptormediated
endocytosis,
binding of ligands
to receptors
triggers vesicle
formation
• A ligand is any
molecule that
binds specifically
to a receptor site
of another
molecule
© 2011 Pearson Education, Inc.
Animation: Receptor-Mediated
Endocytosis
Right-click slide / select “Play”
Figure 7.22
Phagocytosis
Pinocytosis
Receptor-Mediated Endocytosis
EXTRACELLULAR
FLUID
Solutes
Pseudopodium
Receptor
Ligand
Plasma
membrane
Coat proteins
Coated
pit
“Food” or
other particle
Coated
vesicle
Vesicle
Food
vacuole
CYTOPLASM
L.0. 2.12
Enduring understanding 2.B: Growth, reproduction
and dynamic homeostasis require that cells create and
maintain internal environments that are different from
their external environments.
• Essential knowledge 2.B.3: Eukaryotic cells maintain internal
membranes that partition the cell into specialized regions.
a. Internal membranes facilitate cellular processes by minimizing competing interactions and by
increasing surface area where reactions can occur.
b. Membranes and membrane-bound organelles in eukaryotic cells localize (compartmentalize)
intracellular metabolic processes and specific enzymatic reactions. [See also 4.A.2]
• Endoplasmic reticulum
• Mitochondria
• Chloroplasts
• Golgi
• Nuclear envelope
c. Archaea and Bacteria generally lack internal membranes and organelles and have a cell wall.
2.B.3 Learning Objectives
• LO 2.13 The student is able to explain
how internal membranes and organelles
contribute to cell functions. [See SP 6.2]
• LO 2.14 The student is able to use
representations and models to describe
differences in prokaryotic and eukaryotic
cells. [See SP1.4]
Figure 6.5
Fimbriae
Nucleoid
Ribosomes
Plasma
membrane
Bacterial
chromosome
Cell wall
Capsule
0.5 m
(a) A typical
rod-shaped
bacterium
Flagella
(b) A thin section
through the
bacterium Bacillus
coagulans (TEM)
• Eukaryotic cells are characterized by having
– DNA in a nucleus that is bounded by a
membranous nuclear envelope
– Membrane-bound organelles
– Cytoplasm in the region between the plasma
membrane and nucleus
• Eukaryotic cells are generally much larger than
prokaryotic cells
© 2011 Pearson Education, Inc.
Figure 6.8a
ENDOPLASMIC RETICULUM (ER)
Flagellum
Nuclear
envelope
Nucleolus
Rough Smooth
ER
ER
NUCLEUS
Chromatin
Centrosome
Plasma
membrane
CYTOSKELETON:
Microfilaments
Intermediate filaments
Microtubules
Ribosomes
Microvilli
Golgi apparatus
Peroxisome
Mitochondrion
Lysosome
Figure 6.8c
Nuclear
envelope
NUCLEUS
Nucleolus
Chromatin
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Ribosomes
Central vacuole
Golgi
apparatus
Microfilaments
Intermediate
filaments
Microtubules
Mitochondrion
Peroxisome
Chloroplast
Plasma membrane
Cell wall
Wall of adjacent cell
Plasmodesmata
CYTOSKELETON
• Essential knowledge 4.A.2: The structure and
function of subcellular components, and their
interactions, provide essential cellular processes.
a. Ribosomes are small, universal structures
comprised of two interacting parts: ribosomal RNA and
protein. In a sequential manner, these cellular
components interact to become the site of protein
synthesis where the translation of the genetic
instructions yields specific polypeptides. [See also 2.B.3]
b. Endoplasmic reticulum (ER) occurs in two forms:
smooth and rough. [See also 2.B.3]
1. Rough endoplasmic reticulum functions to
compartmentalize the cell, serves as mechanical
support, provides site-specific protein synthesis with
membrane-bound ribosomes and plays a role in
intracellular transport.
2. In most cases, smooth ER synthesizes lipids.
• c. The Golgi complex is a membrane-bound structure
that consists of a series of flattened membrane sacs
(cisternae). [See also 2.B.3]
1. Functions of the Golgi include synthesis and
packaging of materials (small molecules) for transport (in
vesicles), and production of lysosomes.
d. Mitochondria specialize in energy capture and
transformation. [See also 2.A.2, 2.B.3]
1. Mitochondria have a double membrane that
allows compartmentalization within the mitochondria and
is important to its function.
2. The outer membrane is smooth, but the inner
membrane is highly convoluted, forming folds called
cristae.
3. Cristae contain enzymes important to ATP
production; cristae also increase the surface area for
ATP production.
e. Lysosomes are membrane-enclosed sacs that contain hydrolytic
enzymes, which are important in intracellular digestion, the recycling of a
cell’s organic materials and programmed cell death (apoptosis). Lysosomes
carry out intracellular digestion in a variety of ways. [See also 2.B.3]
f. A vacuole is a membrane-bound sac that plays roles in intracellular
digestion and the release of cellular waste products. In plants, a large
vacuole serves many functions, from storage of pigments orpoisonous
substances to a role in cell growth. In addition, a large central vacuole
allows for a large surface area to volume ratio. [See also 2.A.3, 2.B.3]
g. Chloroplasts are specialized organelles found in algae and higher plants
that capture energy through photosynthesis. [See also 2.A.2, 2 B.3]
1. The structure and function relationship in the chloroplast allows
cells to capture the energy available in sunlight and convert it to chemical
bond energy via photosynthesis.
2. Chloroplasts contain chlorophylls, which are responsible for the
green color of a plant and are the key light-trapping molecules in
photosynthesis. There are several types of chlorophyll, but the predominant
form in plants is chlorophyll a.
3. Chloroplasts have a double outer membrane that creates a
compartmentalized structure, which supports its function. Within the
chloroplasts are membrane-bound structures called thylakoids. Energycapturing reactions housed in the thylakoids are organized in stacks, called
“grana,” to produce ATP and NADPH2, which fuel carbon-fixing reactions in
the Calvin-Benson cycle. Carbon fixation occurs in the stroma, where
molecules of CO2 are converted to carbohydrates.
4.A.2 Learning Objectives
• LO 4.4 The student is able to make a prediction about
the interactions of subcellular organelles. [See SP 6.4]
• LO 4.5 The student is able to construct explanations
based on scientific evidence as to how interactions of
subcellular structures provide essential functions. [See
SP 6.2]
• LO 4.6 The student is able to use representations and
models to analyze situations qualitatively to describe
how interactions of subcellular structures, which possess
specialized functions, provide essential functions. [See
SP 1.4]
Concept 6.4: The
X
endomembrane system regulates
protein traffic and performs
metabolic functions in the cell
• Components of the endomembrane system
–
–
–
–
–
–
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
• These components are either continuous or
connected via transfer by vesicles
© 2011 Pearson Education, Inc.
The Endoplasmic Reticulum:
Biosynthetic Factory
• The endoplasmic reticulum (ER) accounts for
more than half of the total membrane in many
eukaryotic cells
• The ER membrane is continuous with the
nuclear envelope
• There are two distinct regions of ER
– Smooth ER, which lacks ribosomes
– Rough ER, surface is studded with ribosomes
© 2011 Pearson Education, Inc.
Figure 6.11
Smooth ER
Nuclear
envelope
X
Rough ER
ER lumen
Cisternae
Ribosomes
Transport vesicle
Smooth ER
Transitional ER
Rough ER
200 nm
Functions of Smooth ER
• The smooth ER
–
–
–
–
Synthesizes lipids
Metabolizes carbohydrates
Detoxifies drugs and poisons
Stores calcium ions
© 2011 Pearson Education, Inc.
Functions of Rough ER
• The rough ER
– Has bound ribosomes, which secrete
glycoproteins (proteins covalently bonded to
carbohydrates)
– Distributes transport vesicles, proteins
surrounded by membranes
– Is a membrane factory for the cell
© 2011 Pearson Education, Inc.
The Golgi Apparatus: Shipping
and
Receiving Center
• The Golgi apparatus consists of flattened
membranous sacs called cisternae
• Functions of the Golgi apparatus
– Modifies products of the ER
– Manufactures certain macromolecules
– Sorts and packages materials into transport
vesicles
© 2011 Pearson Education, Inc.
Figure 6.12
cis face
(“receiving” side of
Golgi apparatus)
0.1 m
Cisternae
trans face
(“shipping” side of
Golgi apparatus)
TEM of Golgi apparatus
Lysosomes: Digestive
Compartments
• A lysosome is a membranous sac of
hydrolytic enzymes that can digest
macromolecules
• Lysosomal enzymes can hydrolyze proteins,
fats, polysaccharides, and nucleic acids
• Lysosomal enzymes work best in the acidic
environment inside the lysosome
© 2011 Pearson Education, Inc.
X
X
Animation: Lysosome Formation
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
• Some types of cell can engulf another cell by
phagocytosis; this forms a food vacuole
• A lysosome fuses with the food vacuole and
digests the molecules
• Lysosomes also use enzymes to recycle the
cell’s own organelles and macromolecules, a
process called autophagy
© 2011 Pearson Education, Inc.
Figure 6.13
X
Nucleus
Vesicle containing
two damaged
organelles
1 m
1 m
Mitochondrion
fragment
Peroxisome
fragment
Lysosome
Digestive
enzymes
Lysosome
Lysosome
Plasma membrane
Peroxisome
Digestion
Food vacuole
Vesicle
(a) Phagocytosis
(b) Autophagy
Mitochondrion
Digestion
Vacuoles: Diverse Maintenance
Compartments
• A plant cell or fungal cell may have one or
several vacuoles, derived from endoplasmic
reticulum and Golgi apparatus
• Food vacuoles are formed by phagocytosis
• Contractile vacuoles, found in many freshwater
protists, pump excess water out of cells
• Central vacuoles, found in many mature plant
cells, hold organic compounds and water
© 2011 Pearson Education, Inc.
Figure 6.15-1
ENDOMEMBRANE SYSTEM – MUST KNOW! X
Nucleus
Rough ER
Smooth ER
Plasma
membrane
Figure 6.15-2
X
Nucleus
Rough ER
Smooth ER
cis Golgi
trans Golgi
Plasma
membrane
Figure 6.15-3
X
Nucleus
Rough ER
Smooth ER
cis Golgi
trans Golgi
Plasma
membrane
Peroxisomes: Oxidation
• Peroxisomes are specialized metabolic
compartments bounded by a single membrane
• Peroxisomes produce hydrogen peroxide and
convert it to water
• Peroxisomes perform reactions with many
different functions
• How peroxisomes are related to other organelles
is still unknown
© 2011 Pearson Education, Inc.
Figure 6.UN01
Nucleus
(ER)
(Nuclear
envelope)
Roles of the Cytoskeleton:
Support and Motility
• The cytoskeleton helps to support the cell and
maintain its shape
• It interacts with motor proteins to produce
motility
• Inside the cell, vesicles can travel along
“monorails” provided by the cytoskeleton
• Recent evidence suggests that the cytoskeleton
may help regulate biochemical activities
© 2011 Pearson Education, Inc.
X
Figure 6.21
ATP
Vesicle
X
Receptor for
motor protein
Motor protein Microtubule
(ATP powered) of cytoskeleton
(a)
Microtubule
(b)
Vesicles
0.25 m
Enduring understanding 4.B: Competition and
cooperation are important aspects of biological
systems.
• Essential knowledge 4.B.1: Interactions between molecules
affect their structure and function.
a. Change in the structure of a molecular system may result in a change of
the function of the system. [See also 3.D.3]
b. The shape of enzymes, active sites and interaction with specific
molecules are essential for basic functioning of the enzyme
1. For an enzyme-mediated chemical reaction to occur, the substrate
must be complementary to the surface properties (shape and charge) of the
active site. In other words, the substrate must fit into the enzyme’s active
site.
2. Cofactors and coenzymes affect enzyme function; this interaction
relates to a structural change that alters the activity rate of the enzyme. The
enzyme may only become active when all the appropriate cofactors or
coenzymes are present and bind to the appropriate sites on the enzyme.
c. Other molecules and the environment in which the enzyme acts can
enhance or inhibit enzyme activity. Molecules can bind reversibly or
irreversibly to the active or allosteric sites, changing the activity of the
enzyme.
d. The change in function of an enzyme can be interpreted from data
regarding the concentrations of product or substrate as a function of time.
These representations demonstrate the relationship between an enzyme’s
activity, the disappearance of substrate, and/or presence of a competitive
inhibitor.
Learning Objective: LO 4.17 The student is able to analyze
data to identify how molecular interactions affect
structure and function. [See SP 5.1]
Concept 8.4: Enzymes speed up metabolic
reactions by lowering energy barriers
• A catalyst is a chemical agent that speeds up a
reaction without being consumed by the reaction
• An enzyme is a catalytic protein
• Hydrolysis of sucrose by the enzyme sucrase is
an example of an enzyme-catalyzed reaction
Sucrase
Sucrose
(C12H22O11)
© 2011 Pearson Education, Inc.
Glucose
(C6H12O6)
Fructose
(C6H12O6)
• Enzyme speed reactions by lowering EA.
– The transition state can then be reached even
at moderate temperatures.
• Enzymes do not change delta G.
– It hastens reactions that would occur
eventually.
– Because enzymes
are so selective,
they determine
which chemical
processes will
occur at any time.
Fig. 6.13
2. Enzymes are substrate
specific
• A substrate is a reactant which binds to an
enzyme.
• When a substrate or substrates binds to an
enzyme, the enzyme catalyzes the
conversion of the substrate to the product.
– Sucrase is an enzyme that binds to sucrose and
breaks the disaccharide into fructose and
glucose.
• The active site of an enzymes is typically a
pocket or groove on the surface of the
protein into which the substrate fits.
• The specificity of an enzyme is due to the
fit between the active site and that of the
substrate.
• As the substrate binds, the enzyme
changes shape leading to a tighter
induced fit, bringing chemical groups in
position to catalyze the reaction.
Fig. 6.14
3. The active site is an enzyme’s
catalytic center
• In most cases substrates are held in the
active site by weak interactions, such as
hydrogen bonds and ionic bonds.
– R groups of a few amino acids on the active site
catalyze the conversion of substrate to product.
Fig. 6.15
Characteristics of Enzymes
1) Enzymes are unaffected by the reaction and are
reusable – in fact, a single enzyme molecule
can catalyze thousands or more reactions a
second.
2) Very specific – only bind one substrate
3) Don’t change the reaction equilibrium
4) Metabolic enzymes can catalyze a reaction in
both the forward and reverse direction.
–
–
The actual direction depends on the relative
concentrations of products and reactants.
Enzymes catalyze reactions in the direction of
equilibrium.
How Enzymes Lower Activation Energy
• Enzymes use a variety of mechanisms to lower
activation energy and speed a reaction.
– The active site orients substrates in the correct
orientation for the reaction.
– As the active site binds the substrate, it may put stress
on bonds that must be broken, making it easier to
reach the transition state.
– R groups at the active site may create a conducive
microenvironment for a specific reaction.
– Enzymes may even bind covalently to substrates in an
intermediate step before returning to normal.
A cell’s physical and chemical
environment affects enzyme activity
• The three-dimensional structures of enzymes
(almost all proteins) depend on
environmental conditions.
• Changes in shape influence the reaction
rate.
• Some conditions lead to the most active
conformation and lead to optimal rate of
reaction.
Things that Influence Reaction Rates
1) The rate that a specific number of enzymes
converts substrates to products depends in part on
substrate concentrations. As add substrate,
speeds up until a certain point = enzyme
saturation.
• At low substrate concentrations, an increase in
substrate speeds binding to available active sites.
• However, there is a limit to how fast a reaction can
occur.
• At some substrate concentrations, the active sites
on all enzymes are engaged, called enzyme
saturation.
2) Enzyme concentration
3) Temperature has a major impact on
reaction rate.
– As temperature increases, collisions between
substrates and active sites occur more
frequently as molecules move faster.
– However, at some point thermal agitation begins
to disrupt the weak bonds that stabilize the
protein’s active conformation and the protein
denatures.
– Each enzyme has an optimal temperature.
Fig. 6.16a
4) Because pH also influences shape and
therefore reaction rate, each enzyme has
an optimal pH too.
• This falls between pH 6 - 8 for most
enzymes.
• However, digestive enzymes in the
stomach are designed to work best at pH 2
while those in the intestine are optimal at
pH 8, both matching their working
environments.
Fig. 6.16b
5) Ion concentration – salts and other ions – their
charges may disrupt charged R-groups that
determine shape of protein’s active site
6) Many enzymes require nonprotein helpers,
cofactors, for catalytic activity.
– They bind permanently to the enzyme or reversibly.
– Some inorganic cofactors include zinc, iron, and
copper.
• Organic cofactors, coenzymes, include vitamins
or molecules derived from vitamins.
• The manners by which cofactors assist catalysis
are diverse.
7) Binding by some molecules, inhibitors,
prevent enzymes from catalyzing reactions.
– If binding involves covalent bonds, then
inhibition is often irreversible.
– If binding is weak, inhibition may be reversible.
• If the inhibitor binds to the same site as the
substrate, then it blocks substrate binding
via competitive inhibition.
Fig. 6.17a, b
• If the inhibitor binds somewhere other than
the active site, it blocks substrate binding
via noncompetitive inhibition.
• Binding by the inhibitor causes the enzyme
to change shape, rendering the active site
unreceptive at worst or less effective at
catalyzing the reaction.
• Reversible inhibition of enzymes is a
natural part of the regulation of metabolism.
Fig. 6.17c
Let’s look at a model enzyme-catalyzed
reaction
• http://www.kscience.co.uk/animations/model.swf
• Setup each and then record trend:
–
–
–
–
–
1) control E(5), S(20), T(40), pH(7) vol(300)
2) increase enzyme (15)
3) increase substrate (40)
4) non-optimal temp (0 and 60)
5) non-optimal pH (10) Note: this particular model uses an
enzyme that favors acid pH
– Then try E(10), S(60) and rest as for control – notice how
rate of reaction slows
In general…
• More enzyme = faster reaction rate
• More substrate up to a certain point = faster
reaction rate
• Too high/too low temp = slower reaction rate
• Too high/too low pH = slower reaction rate
• With inhibitors= slower reaction rate
Regulation of enzyme activity helps
control metabolism
• Chemical chaos would result if a cell’s
metabolic pathways were not tightly regulated
• A cell does this by switching on or off the
genes that encode specific enzymes or by
regulating the activity of enzymes
© 2011 Pearson Education, Inc.
Allosteric Regulation of Enzymes
• Allosteric regulation may either inhibit or
stimulate an enzyme’s activity
• Allosteric regulation occurs when a regulatory
molecule binds to a protein at one site and
affects the protein’s function at another site
© 2011 Pearson Education, Inc.
Figure 8.19
(b) Cooperativity: another type of allosteric activation
(a) Allosteric activators and inhibitors
Allosteric enzyme
with four subunits
Active site
(one of four)
Regulatory
site (one
of four)
Substrate
Activator
Inactive form
Stabilized active form
Active form
Oscillation
Nonfunctional
active site
Inactive form
Inhibitor
Stabilized inactive
form
Stabilized active
form
• Cooperativity is a form of allosteric regulation
that can amplify enzyme activity
• One substrate molecule primes an enzyme to
act on additional substrate molecules more
readily
• Cooperativity is allosteric because binding by a
substrate to one active site affects catalysis in
a different active site
© 2011 Pearson Education, Inc.
Identification of Allosteric
Regulators
• Allosteric regulators are attractive drug
candidates for enzyme regulation because of
their specificity
• Inhibition of proteolytic enzymes called
caspases may help management of
inappropriate inflammatory responses
© 2011 Pearson Education, Inc.
Figure 8.20
EXPERIMENT
Caspase 1
Active
site
Substrate
SH
Active form can
bind substrate
SH
Known active form
SH
Allosteric
binding site
Known inactive form
Allosteric
inhibitor
Hypothesis: allosteric
inhibitor locks enzyme
in inactive form
RESULTS
Caspase 1
Inhibitor
Active form
Allosterically
inhibited form
Inactive form
Feedback Inhibition
• In feedback inhibition, the end product of a
metabolic pathway shuts down the pathway
• Feedback inhibition prevents a cell from
wasting chemical resources by synthesizing
more product than is needed
© 2011 Pearson Education, Inc.
Figure 8.21
Active site
available
Isoleucine
used up by
cell
Active site of
Feedback
enzyme 1 is
inhibition
no longer able
to catalyze the
conversion
of threonine to
intermediate A;
pathway is
switched off. Isoleucine
binds to
allosteric
site.
Initial
substrate
(threonine)
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Intermediate A
Enzyme 2
Intermediate B
Enzyme 3
Intermediate C
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine)
L.O. 4.17
• Essential knowledge 4.B.2: Cooperative interactions within
organisms promote efficiency in the use of energy and matter.
a. Organisms have areas or compartments that perform a subset of
functions related to energy and matter, and these parts contribute to
the whole. [See also 2.A.2, 4.A.2]
1. At the cellular level, the plasma membrane, cytoplasm and,for
eukaryotes, the organelles contribute to the overall specialization and
functioning of the cell.
2. Within multicellular organisms, specialization of organs contributes
to the overall functioning of the organism.
• Exchange of gases
• Circulation of fluids
• Digestion of food
• Excretion of wastes
3. Interactions among cells of a population of unicellular organisms
can be similar to those of multicellular organisms, and these interactions
lead to increased efficiency and utilization of energy and matter.
Learning Objective: LO 4.18 The student is able to use
representations and models to analyze how cooperative interactions
within organisms promote efficiency in the use of energy and matter.
[See SP 1.4]
Enduring understanding 4.C: Naturally occurring diversity among
and between components within biological systems affects
interactions with the environment.
• Essential knowledge 4.C.1: Variation in molecular units
provides cells with a wider range of functions.
•
a. Variations within molecular classes provide cells and organisms with a
wider range of functions. [See also 2.B.1, 3.A.1, 4.A.1, 4.A.2]
• Different types of phospholipids in cell membranes
• Different types of hemoglobin
• MHC proteins
• Chlorophylls
• Molecular diversity of antibodies in response to an antigen
b. Multiple copies of alleles or genes (gene duplication) may provide new
phenotypes. [See also 3.A.4, 3.C.1]
1. A heterozygote may be a more advantageous genotype than a
homozygote under particular conditions, since with two different alleles, the
organism has two forms of proteins that may provide functional resilience in
response to environmental stresses.
2. Gene duplication creates a situation in which
one copy of the gene maintains its original
function, while the duplicate may evolve a new
function.
• The antifreeze gene in fish
• Learning Objective: LO 4.22 The student is able
to construct explanations based on evidence of
how variation in molecular units provides cells
with a wider range of functions. [See SP 6.2]