Transcript Metabolism 1 PPT

BSC 2010 - Exam I Lectures and Text Pages
• I. Intro to Biology (2-29)
• II. Chemistry of Life
–
Chemistry review (30-46)
–
Water (47-57)
–
Carbon (58-67)
–
Macromolecules (68-91)
• III. Cells and Membranes
–
Cell structure (92-123)
–
Membranes (124-140)
• IV. Introductory Biochemistry
–
Energy and Metabolism (141-159)
–
Cellular Respiration (160-180)
–
Photosynthesis (181-200)
Energy & Metabolism
• Metabolism, Energy and Life
– Metabolism = all of an organism’s chemical
rxns and energy conversions
– Metabolism transforms the energy and
material resources of a cell
– Cells use energy to perform various types
of work
– Metabolic reactions occur in specific
pathways, catalyzed by specific enzymes
(proteins)
The Energy of Life
• The living cell
–
Is a miniature factory where thousands of reactions occur
–
Converts energy in many ways and uses energy to perform work,
such as active transport.
• Some organisms convert energy to light, as in
bioluminescence
Figure 8.1
Organization of the Chemistry of Life into
Metabolic Pathways
• A metabolic pathway has many steps
– That begin with a specific molecule and end
with a product
– That are each catalyzed by a specific enzyme
Enzyme 1
A
Enzyme 3
D
C
B
Reaction 1
Starting
molecule
Enzyme 2
Reaction 2
Reaction 3
Product
Catabolic Pathways
– Break down larger molecules into smaller ones
– Release energy that can be captured in the
bonds of ATP
– Example: Cellular Respiration (glucose 
CO2 + H2O + ATP)
Anabolic Pathways
– Synthesize complicated molecules from simpler
ones
– Consume energy (use ATP or another E source)
– are biosynthetic pathways (use energy)
– Example: Photosynthesis (CO2 + H2O + sunlight
energy  O2 + glucose)
Energy Coupling
• Anabolism is fueled by the energy
released from catabolism
– Anabolic pathways use the energy
produced by catabolic pathways. The
transfer of energy is accomplished by ATP.
Forms of Energy
• Energy
– Is the capacity to cause change, to do work, to
move or rearrange matter
– Exists in various forms, of which some can
perform work
Kinetic Energy
– Is the energy associated with motion/work
– Ex = leg muscles turning a bike wheel
– Heat = thermal energy = kinetic energy assoc. w/
random movement of molecules
– Moving matter does work by transferring its motion
to other matter.
Potential Energy
– Is energy stored in the location or structure
of matter
– Includes chemical energy – potential energy
available from a reaction that is stored in the
arrangement of atoms in molecules
Energy Can Be Converted
– From one form to
another
– Plants convert light
energy (kinetic) into
chemical energy
(potential) in
sugars.
Figure 8.2
On the platform, a diver
has more potential energy.
Climbing up converts kinetic
energy of muscle movement
to potential energy.
Diving converts potential
energy to kinetic energy.
In the water, a diver has
less potential energy.
Metabolism is Subject to the Laws of Thermodynamics
• An organism’s metabolism transforms matter
and energy into various forms, but always
subject to the laws of thermodynamics
The Laws of Energy Transformation
• Thermodynamics
– Is the study of energy transformations
• A System = matter under study
– a. Closed system is isolated from surroundings
– b. Open system = energy can be transferred
between the system & surroundings
• Ex = organisms
The First Law of Thermodynamics
• According to the first law of
thermodynamics energy
cannot be created or
destroyed
• The energy of the universe is
constant. This is the principle
of the conservation of energy
• So energy can be transferred &
transformed but NOT created
or destroyed
Figure 8.3
Chemical
energy
(a) First law of thermodynamics: Energy
can be transferred or transformed but
Neither created nor destroyed. For
example, the chemical (potential) energy
in food will be converted to the kinetic
energy of the cheetah’s movement in (b).
The Second Law of Thermodynamics
• According to the second law of thermodynamics,
spontaneous changes that do not require outside
energy increase the entropy, or disorder, of the
universe
Heat
co2
+
H2O
Figure 8.3
(b) Second law of thermodynamics: Every energy transfer or transformation increases
the disorder (entropy) of the universe. For example, disorder is added to the cheetah’s
surroundings in the form of heat and the small molecules that are the by-products
of metabolism.
The Second Law of Thermodynamics
• Every energy transformation/transfer increases the
entropy (disorder) of the universe.
–
No energy transfer is 100% efficient, some is always
converted to heat.
–
Heat (kinetic energy) has a high entropy value. It is the
least ordered form of energy.
• Order can increase locally (energy input), but is constantly
decreasing globally
–
Organisms are low-entropy islands in an increasingly random
universe. They live at the expense of free energy. Organisms
are open systems and can become more ordered, but only with
the input of energy, and that is at the expense of the
surroundings. Organisms take in food (a highly ordered form of
energy) and put out heat, water, and carbon dioxide.
Biological Order and Disorder
• Living systems
– Increase the entropy of the universe
– Use energy to maintain order
50µm
Figure 8.4
Buttercup root cross-section
Organisms Live at the Expense of FREE ENERGY
The reactions in our bodies use up energy. Reactions will
only run without the input of additional outside energy IF
they are spontaneous reactions. Non-spontaneous
reactions require the input of outside energy.
• a. Reactions that happen on their own (w/out energy
input) are spontaneous. Spontaneous processes always
increase entropy.
• b. “How do we know if a rxn is spontaneous?” It
occurs without the input of external energy and it will only
do so if it decreases the free energy of the system.
Organisms Live at the Expense of FREE ENERGY
Gibbs free energy (G) is the portion of a system’s energy
that is available to do work when temperature and
pressure are held constant.
• Reactions with a -∆G are spontaneous. Those
reactions decrease the total free energy and/or
increase the disorder (entropy [S]) and thereby
increase the stability of the system.
Change in Free Energy
• The change in free energy, ∆G during a
biological process
– Is related directly to the enthalpy change (∆H)
and the change in entropy
∆G = ∆H – T∆S
H = enthalpy (total energy in biological systems)
S = entropy (disorder, energy not available for work)
T = temperature (K = C + 273)
An unstable system is rich in free energy and has a
tendency to change to a more stable state and
potentially perform work in the process.
Free Energy and Equilibrium or “Why Care About Spontaneity”?
In terms of rxn equilibriums (see Ch 2):
• a. ∆G = Gfinal - Ginitial (smaller value is more stable)
• b. Equilibrium = state of maximum stability
• c. When equilibrium reached  G is lowest in that system
• d. In chemical reactions, equilibrium is when the forward and
backward reactions proceed at the same rate and ∆G = 0, so no net
free energy change.
• e. A cell that has reached equilibrium is DEAD (∆G is lowest & no
work can be done)
–
Lack of equilibrium (life) maintained by making products of one
rxn the reactants of another (with a steady supply of glucose + O2)
–
Organisms are open systems. Life is constantly supplied with
free E from the sun. That energy must be added to the system
to move it away from equilibrium (death).
Free Energy, Stability, and Equilibrium
• Organisms live at the expense of free energy
• During a spontaneous change
– Free energy decreases and the stability of a
system increases
At Maximum Stability
– The system is at equilibrium
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneously 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. Objects
move spontaneously from a
higher altitude to a lower one.
Figure 8.5
(b) Diffusion. Molecules
in a drop of dye diffuse
until they are randomly
dispersed.
(c) Chemical reaction. In a
cell, a sugar molecule is
broken down into simpler
molecules.
Free Energy and Metabolism
Free E and living systems (metabolism):
a. Exergonic rxn (fig 8.6a) = E releasing (negative ∆G)  spontaneous
The greater the decrease in ∆G  greater amt of work can be done
Ex: Respiration
∆G for C6H12O6 + O2  6CO2 + 6H2O = -686 kcal/mol
b. Endergonic rxn (fig 8.6b) = E absorbing (positive ∆G)  NOT spontaneous
Sunlight (E) drives photosynthesis (reverse of respiration)
∆G for 6CO2 + 6H2O  C6H12O6 + O2 = +686 kcal/mol
c. The energy released by an exergonic reaction (-∆G) is equal to the energy
required by the reverse endergonic reaction (+∆G)
d. Metabolic disequilibrium is essential to life. Respiration and other cell
reactions are reversible and could reach equilibrium if the cell did not maintain a
supply of reactants and use up or dispose of products.
e. The cell must couple the energy of exergonic processes to power endergonic
processes.
Exergonic and Endergonic Reactions in Metabolism
• An exergonic reaction
– Proceeds with a net release of free energy
and is spontaneous
Free energy
Reactants
Amount of
energy
released
(∆G <0)
Energy
Products
Progress of the reaction
Figure 8.6
(a) Exergonic reaction: energy released
Exergonic and Endergonic Reactions in Metabolism
• An endergonic reaction
– Is one that absorbs free energy from its
surroundings and is nonspontaneous
Free energy
Products
Energy
Reactants
Progress of the reaction
Figure 8.6
(b) Endergonic reaction: energy required
Amount of
energy
required
(∆G>0)
Equilibrium and Metabolism
• Reactions in a closed system
– Eventually reach equilibrium
∆G < 0
Figure 8.7 A
∆G = 0
(a) A closed hydroelectric system. Water flowing downhill turns a turbine
that drives a generator providing electricity to a light bulb, but only until
the system reaches equilibrium.
Maintaining Disequilibrium in Living Systems
• Cells in our body
– Experience a constant flow of materials in and
out, preventing metabolic pathways from
reaching equilibrium
(b) An open hydroelectric
system. Flowing water
keeps driving the generator
because intake and outflow
of water keep the system
from reaching equlibrium.
Figure 8.7
∆G < 0
An analogy for cellular respiration
∆G < 0
∆G < 0
∆G < 0
Figure 8.7
(c) A multistep open hydroelectric system. Cellular respiration is
analogous to this system: Glucoce is broken down in a series
of exergonic reactions that power the work of the cell. The product
of each reaction becomes the reactant for the next, so no reaction
reaches equilibrium.
ATP – Energy Currency of the Cell
ATP powers cellular work by coupling exergonic
reactions to endergonic reactions
• Energy coupling
– Is a key feature in the way cells manage their
energy resources to do work
• A cell does three main kinds of work
– Mechanical
– Transport
– Chemical
The Structure and Hydrolysis of ATP
• ATP (adenosine triphosphate)
– Is the cell’s energy shuttle
Adenine
N
O
O
-O
O
-
O
-
Phosphate groups
Figure 8.8
O
O
C
C
N
HC
O
O
O
NH2
N
CH2
-
O
H
N
H
H
H
OH
CH
C
OH
Ribose
Energy is released from ATP
– When the terminal phosphate bond is broken
P
P
P
Adenosine triphosphate (ATP)
H2O
P
i
+
Figure 8.9 Inorganic phosphate
P
P
Adenosine diphosphate (ADP)
Energy
ATP hydrolysis (and the energy released)
–
Can be coupled to other reactions
Endergonic reaction: ∆G is positive, reaction
is not spontaneous
NH2
Glu
+
Glutamic
acid
NH3
Glu
Ammonia
Glutamine
∆G = +3.4 kcal/mol
Exergonic reaction: ∆ G is negative, reaction
is spontaneous
ATP
Figure 8.10
+
H2O
ADP +
Coupled reactions: Overall ∆G is negative;
together, reactions are spontaneous
P
∆G = - 7.3 kcal/mol
∆G = –3.9 kcal/mol
How ATP Performs Work
• ATP drives endergonic reactions
– By phosphorylation, ATP transfers a highenergy phosphate to other molecules
– Energy to perform work becomes available
when the phosphate is released from its
substrate.
The three types of cellular work
• Are powered by the hydrolysis of ATP
P
i
P
Motor protein
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
Membrane
protein
ADP
+
ATP
P
P
Solute
P
i
Solute transported
(b) Transport work: ATP phosphorylates transport proteins
P
Glu + NH3
Reactants: Glutamic acid
and ammonia
Figure 8.11
NH2
Glu
+
P
i
Product (glutamine)
made
(c) Chemical work: ATP phosphorylates key reactants
i
The Regeneration of ATP
• Catabolic pathways provide energy to
– Drive the regeneration of ATP from ADP and
phosphate
ATP hydrolysis to
ADP + P i yields energy
ATP synthesis from
ADP + P i requires energy
ATP
Energy from catabolism
(exergonic, energy yielding
processes)
Figure 8.12
Energy for cellular work
(endergonic, energyconsuming processes)
ADP + P
i