Transcript VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont

UNIT IV – CELLULAR ENERGY
HillisCh 2.5, 6
Big Campbell ~
Ch 8,9,10
Baby Campbell ~
Ch 5,6,7
I. THE WORKING CELL
• Metabolism
 Totality (sum) of an organism’s chemical reactions
 Catabolic Pathways Breaks down molecules; releases energy; EX: Cellular Respiration
 Anabolic Pathways Pathway that synthesizes larger molecules from smaller ones;
requires energy; EX: synthesis of AA, synthesis of proteins
I. THE WORKING CELL, cont
• Energy
•
 Kinetic Energy –energy associated with the relative motion of objects.
EX: pool stick  cue ball  other balls
 Potential Energy – energy that matter possesses (stored) because of
its location or structure. EX: water behind a dam
 Chemical Energy – Potential energy of molecules
Thermodynamics
 First Law of Thermodynamics states that total amount of energy in
universe is constant – can be transferred or transformed, but it cannot
be created or destroyed
 Principle of the Conservation of Energy
 Second Law of Thermodynamics states that energy is lost to the
environment as heat; that is, some energy becomes unusable
EX: Bear catching fish for food
 Entropy – measure of disorder or randomness that is a
consequence of the loss of useable energy during energy
transfer.
I. THE WORKING CELL, cont
• Chemical Reactions are classified according to whether they
require or produce energy
 Endergonic – Requires net input of energy. Energy is then
stored in products as potential energy.
 Exergonic - Release energy.
 Energy Coupling – Often used in cellular metabolism. Energy
released in exergonic rxn is used to drive endergonic rxn.
ATP . . . It’s energy
1 – 2 – 3 . . . In bonds of P
ATP . . . Energy
Energy in the bonds of P! 
II. ATP
• Powers 3 kinds of work:
- Chemical (synthesis of polymers)
- Transport (pumping substances across the membrane)
- Mechanical (beating of cilia, contraction of muscle cells, chromosome
movement)
II. ATP
• Adenosine Triphosphate
 Nucleotide that stores &
provides usable energy to
the cell
 Structure of ATP
 5-C Sugar called Ribose
 Nitrogen base Adenine
 3 Phosphate groups
 ATP contains potential
energy, especially between
2nd and 3rd phosphate
groups.
P – P bond is unstable
Easily broken by
HYDROLYSIS
II. ATP, cont
• ATP → ADP + Pi
 Catabolic Pathway
 Exergonic
 Coupled with endergonic rxn –
specifically, by transferring
phosphate group from ATP to
another molecule.
II. ATP, cont
• ADP + Pi → ATP
 Anabolic pathway
 Endergonic
 Mechanisms for “making” ATP
Substrate-level Phosphorylation –
enzyme transfers a P from a substrate
molecule to an ADP (organic molecule
generated as an intermediate)
Oxidative Phosphorylation – powered
by the redox reactions of the ETC (on
the membranes) during chemiosmosis
Photophosphorylation – generation
of ATP in the light reactions using
chemiosmosis
II. ATP, cont
Substrate-Level Phosphorylation vs. Oxidative/Photo
Phosphorylation
II. ATP, cont
• In a human, 10 million molecules of ATP are “made” and
“used” per second!!
• We use 1 X 1025 (10,000,000,000,000,000,000,000,000 or
10 quadrillion) molecules of ATP per day!!
• That translates to 100 lbs of ATP . . . At any given
moment, the amount present is ~ 2 oz!!
• A working muscle cell recycles its entire supply of ATP in
less than a minute!!
• Bacteria contain a 1 second supply of ATP!!
III. ♪ ♫ THE CYCLE OF LIFE ♪ ♫
• Photosynthesis
o 6CO2 + 6H2O + sun  C6H12O6 + 6O2
o Occurs in the chloroplasts of plants
CO2 + H2O
• Cellular Respiration
Organic
o C6H12O6 + 6O2  6CO2 + 6H2O + ATP
molecules + O2
o Occurs in the mitochondria of
plants and animals
IV. ENERGY IN THE CELL
• Oxidation-Reduction Reactions
o Energy yield in catabolism comes from transfer of electrons
o Movement of electrons releases chemical energy of molecule
 Released energy used to generate ATP from ADP and Pi
o Known as redox reaction
 One molecule loses an electron and a 2nd molecule gains an e Oxidation
 Electron donor (which is oxidized)is known as reducing agent
(EX: glucose)
 Reduction
 Electron acceptor (which is reduced)is known as oxidizing
agent (EX: O2)
o Electron movement in molecules often traced by changes in H
atom distribution
IV. ENERGY IN THE CELL, cont
• Oxidation-Reduction Reactions, cont
Reactants
Products
Becomes oxidized
Becomes reduced
Reducing
agent methane
Oxidizing
agent oxygen
Carbon dioxide
Water
IV. ENERGY IN THE CELL, cont
• Importance of Electron Carriers
o Energy contained in molecules (for
example, glucose) must be released in a
series of steps
 Electrons released as hydrogen atoms
with corresponding proton
 Hydrogen atoms are passed to an
electron carrier
o Electron carriers are coenzymes
o “Carry” 2 electrons in the form of H-atoms
o Allow for maximum energy transfer,
minimum energy loss
IV. ENERGY IN THE CELL, cont
• Electron Carriers
 NAD+
 Nicotinamide adenine
dinucleotide
 Electron acceptor in cellular
respiration
 Reduced to _NADH_
 FAD
 Flavin adenine dinucleotide
 Electron acceptor in Krebs Cycle
 Reduced to _FADH2__
 NADP+
 Nicotinamide adenine
dinucleotide phosphate
 Electron acceptor in light reaction
of photosynthesis
 Reduced to _NADPH_
IV. ENERGY IN THE CELL, cont
• A Closer Look at Electron
Carriers
 Reduction of NAD+
o Dehydrogenase oxidizes
substrate by removing 2 Hatoms
o NAD+ is reduced, creating
NADH + H+
o NADH shuttles electrons to
electron transport chain.
Electrons “fall” down to oxygen
in a series of steps, each
releasing energy in small
amounts.
V. PHOTOSYNTHESIS – AN OVERVIEW
• Photosynthesis – Process of capturing light energy and
converting it to chemical energy
• Endergonic – b/c e- increase in potential energy as they move
from water to sugar.
• Plants are _Producers_; also known as _Autotrophs_
• Redox Reaction
becomes oxidized
• 6CO2 + 6H2O + sunlight C6H12O6 + 6O2
becomes reduced (e- added)
o Water is split and e- are transferred with H+ to CO2, reducing
it to sugar.
V. PHOTOSYNTHESIS – AN OVERVIEW
Chloroplast Structure
oThylakoids –
oSite of Light Reaction
oFirst step in
photosynthesis
oGrana
oStroma
oSite of Calvin Cycle
oSecond step in
photosynthesis
V. PHOTOSYNTHESIS – AN OVERVIEW, cont
• Location of
Photosynthesis
o Occurs in region
of leaf known as
mesophyll
o Cells contain
abundant
chloroplasts
o CO2 enters leaf
through openings
known as stomata
o H2O enters via
roots; transported
up the xylem
V. PHOTOSYNTHESIS OVERVIEW, cont
Oxidation
Reduction
V. PHOTOSYNTHESIS OVERVIEW, cont
• Sunlight: giant thermonuclear reactor – energy comes from
fusion reactions similar to those in a hydrogen bomb.
• When light hits matter, it can be reflected, transmitted, or
absorbed.
VI. LIGHT REACTION OF PHOTOSYNTHESIS
• Occurs in thylakoid membranes
• Converts light energy to chemical energy
• Light energy
o Visible light is a small portion of the electromagnetic spectrum.
o Light absorbed by chlorophyll and other photosynthetic pigments to power
reactions is not seen. Light not utilized by plant is reflected & seen by human
eye. (Leaf appears green b/c it reflects green &absorbs red and blue light)
o Light energy measured in photons, which each have a fixed quantity of energy
inversely related to the wavelength.
VI. LIGHT REACTION OF PHOTOSYNTHESIS,
cont
• Photosynthetic pigments (substances that absorb visible
light)
• Chlorophyll a – absorbs mainly
blue-violet and red light
• Chlorophyll b – absorbs mainly
blue and orange light
• Cartenoids – other accessory
pigments; expand spectrum of
light energy that can be used
for photosynthesis
carotenoid
xanthophyll
Chlorophyll a
Chlorophyll b
VI. LIGHT REACTION OF PHOTOSYNTHESIS,
cont
• The ability of a pigment to
absorb various
wavelengths of light can
be measured with a
spectrophometer which
directs beams of light of
different wavelengths
through a solution of
pigment and measures
light transmitted at each
wavelength.
VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont
VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont
• A photon of light energy
is absorbed by pigment
molecule in
Photosystem II.
• Energy is passes from
one molecule to
another until it reaches
P680 - pair of
chlorophyll a molecules.
• Electron in each is
excited to higher energy
state – transferred to
primary electron
acceptor.
• Water is split to replace
electron lost by P680.
O2 is released. H+ ions
remain.
VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont
• Excited electron moves from primary electron acceptor to Photosystem I
via electron transport chain. As electron “falls”, energy is released. Used
to synthesize ATP through chemiosmosis.
• Known as photophosphorylation
VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont
• Light energy is transferred via light-harvesting complexes to P700 in
Photosystem I.
• Excited electron is captured by primary electron acceptor. P700’s electron is
replaced by electron transport chain on Photosystem II.
• Electron from P700 moves through a short electron transport chain, reducing
NADP+ to NADPH.
VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont
Linear Electron Flow
VI. LIGHT REACTION OF PHOTOSYNTHESIS, cont
• Cyclic Electron
Flow
o Alternative pathway
seen in some
bacteria, plants
o May be
photoprotective in
plants
o Only utilizes
Photosystem I
o No NADPH
production
o No O2 release
o Does generate ATP
VII. CALVIN CYCLE OF PHOTOSYNTHESIS
• Also known as Dark Reaction, Light-Independent Rxn
• Occurs in stroma of chloroplasts
• “Synthesis” part of photosynthesis; utilizes ATP,
NADPH generated in Light Reaction + CO2 to produce
organic molecules
• Anabolic; endergonic
• Requires enzyme Rubisco
• Three basic steps
 Carbon Fixation
 Reduction
 Regeneration of RuBP
VII. CALVIN CYCLE OF PHOTOSYNTHESIS, cont
VIII. PHOTORESPIRATION
• Counterproductive pathway that produces 2-C molecule,
which is then released as CO2
• Due to oxygen competing for active site of Rubisco
• Consumes ATP; decrease carbohydrate yield
VIII. PHOTORESPIRATION, cont
Plant Adaptations
IX. CELLULAR RESPIRATION – AN OVERVIEW
• Process used by cells to convert chemical energy in glucose (and
other molecules) to ATP
• Primarily takes place in mitochondria of eukaryotic cells
• Overall Reaction
becomes oxidized
• C6H12O6 + 6O2  6CO2 + 6H2O + energy
becomes reduced
• Steps in Cellular Respiration
 Glycolysis
 “Sugar-breaking”
 Initial breakdown of glucose to intermediate, some ATP
 Citric Acid Cycle
 Completes oxidation of glucose to CO2
 Produces ATP, but more importantly provides high-energy electrons for etc
 Electron Transport Chain
 Oxidative Phosphorylation
 Highest ATP yield; uses energy released from downhill flow of electrons to generate ATP
 Citric Acid Cycle + Electron Transport Chain = Oxidative Respiration
IX. CELLULAR RESPIRATION OVERVIEW, cont
X. GLYCOLYSIS
•
•
•
•
Occurs in cytosol of cell
Does not require oxygen
First part of pathway is energy investment phase
Second part of pathway is energy pay-off phase
Energy Investment Phase
X. GLYCOLYSIS, cont
Energy Pay-Off Phase
X. GLYCOLYSIS, cont
• Summary of Glycolysis
XI. OXIDATIVE RESPIRATION
• 2 pyruvates formed from glycolysis still contain a
tremendous amount of chemical energy
• If oxygen is available, pyruvate enters mitochondrion
for citric acid cycle and further oxidation
• Upon entering mitochondrion but prior to entering
citric acid cycle
o “Grooming” Step
Carboxyl group of pyruvate is removed, given off as CO2
Remaining 2-C molecule is oxidized to acetate → NAD+
reduced to NADH + H+
Acetate binds to molecule known as Coenzyme A to form
acetyl CoA
XI. OXIDATIVE RESPIRATION, cont
Grooming Step
XI. OXIDATIVE RESPIRATION, cont
• In the citric acid cycle
(AKA Krebs cycle,
tricarboxylic acid cycle,
TCA cycle), 2-C
molecule goes through
a series of redox rxns.
• Occurs in mitochondrial
matrix
• Produces NADH, FADH2,
ATP, and CO2.
• CoA is not actually a
part of the reaction . . .
it is recycled . . .
remember, it is an
enzyme!
XI. OXIDATIVE RESPIRATION, cont
• A Closer Look at the Citric Acid Cycle
XI. OXIDATIVE RESPIRATION, cont
• Electron Transport – Oxidative
Phosphorylation
o Traditionally called Electron
Transport, now more
commonly called Oxidative
Phosphorylation.
o Occurs in inner
mitochondrial membrane
 Membrane organized into
cristae to increase surface
area
o Two components to
Oxidative Phosphorylation
 Electron Transport Chain
 Chemiosmosis
XI. OXIDATIVE RESPIRATION, cont
• Electron Transport Chain
 Collection of molecules, each more
electronegative than the one before
it
 Molecules are reduced, then
oxidized as electrons are passed
down the chain
 Oxygen is ultimate electron acceptor
 Purpose is to establish H+ gradient
on two sides of inner mitochondrial
membrane
 Energy from “falling electrons” used
to pump H+ from matrix into
intermembrane space
XI. OXIDATIVE RESPIRATION, cont
• Chemiosmosis
 Enzyme complexes known as
ATP synthases located in inner
mitochondrial membrane
 H+ electrochemical gradient
provides energy
 Known as proton motive force
 Movement of H+ ions through
membrane rotates enzyme
complex
 Rotation exposes active sites in
complex
 ATP is produced from ADP and Pi
XI. OXIDATIVE RESPIRATION, cont
• A summary of electron transport . . .
XII. CELLULAR RESPIRATION – A SUMMARY
• Each NADH shuttled through ETC results in approximately _________ ATP
• Each FADH2 shuttled through ETC results in approximately _________ ATP.
• Total ATP Gain in Cellular Respiration =
____ (glycolysis) + ____ (citric acid cycle) + ____ (oxidative phosphorylation) = _____ ATP / glucose
XIII. CELLULAR RESPIRATION & OTHER FOOD
MOLECULES
XIV. METABOLIC POISONS
• Blockage of Electron Transport Chain
• Inhibition of ATP Synthase
• “Uncouplers”
o Prevent creation of H+ ion gradients due to leakiness of
mitochondrial membrane
XV. FERMENTATION
• Anaerobic pathway
• Occurs in cytosol
• Purpose
o In glycolysis, glucose is oxidized to 2 pyruvate, 2 NAD+ are
reduced to 2 NADH, and there is a net gain of 2 ATP
o In oxidative respiration, NADH is oxidized back to NAD+ in
electron transport chain
o If oxygen is not present, another mechanism must be
available to regenerate NAD+ or glycolysis cannot continue
o In fermentation, pyruvate is reduced thereby oxidizing
NADH to NAD+
o Allows glycolysis and net gain of 2 ATP per glucose to
continue
XV. FERMENTATION, cont
XV. FERMENTATION, cont