Download 1 Chapter 8 Energy and Metabolism All reactions within the body

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Chapter 8
Energy and Metabolism
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All reactions within the body require energy for metabolism.
-Metabolism includes all of the chemical reactions in an organism.
-These reactions are ordered into metabolic pathways, a sequence of steps, each controlled by
an enzyme, which covert a specific molecule to a product.
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There are 2 primary types of metabolism:
1) Anabolism – building up; synthesis
-Requires energy
-Example: Photosynthesis
2) Catabolism – breaking down; decomposition
-Releases energy
-Example: Cellular respiration
2 forms of energy
-Energy has been defined as the capacity to cause change
1) Kinetic energy is the energy of motion, of matter that is moving.
-This matter does its work by transferring its motion to other matter.
-Thermal energy (heat) = the kinetic energy of randomly moving molecules
2) Potential energy is the capacity of matter to cause change as a result of location or arrangement
-Chemical Energy = a form of potential energy that is available for release in chemical reactions
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The Laws of Energy Transformations
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Thermodynamics is the study of energy and its application to energy systems.
1st Law of Thermodynamics (Law of Conservation of Energy): Energy can’t be created or destroyed
but can be transferred or transformed
-Energy can be converted from one form to another
-Example: plants convert light energy to the chemical energy in sugar, and cells release this
potential energy to drive cellular processes
nd
2 Law of Thermodynamics: Every energy transfer or transformation results in entropy and
constant energy loss
-Entropy increases when energy is lost.
-10% rule: only 10% of energy is transferred in a reaction, and the other 90% is lost into the
environment in an unusable form.
-We’re always working against entropy: decrease in entropy means decrease in energy, which
means that organisms must have a constant input of energy in order to compensate for this
energy loss
Two forces govern energy conversions:
1. Entropy – measure of randomness/disorder
2. Enthalpy – the amount of available heat
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Free Energy
Free Energy Change
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Free energy is the measure of energy available to do work
WORK:
1) Transport and movement
2) Biochemical reaction (synthesis)
3) Reproduction and growth
*Free energy is stored as ATP, in the last high energy phosphate bond
Gibbs free energy measures the changes in free energy and tells us whether or not the reaction
occurs spontaneously
ΔG = ΔH – TΔS
*Reactions favored are those in which:
a. +Δ S (= entropy: disorder/randomness)
b. – ΔH (=enthalpy: total energy of a system)
Reactions occur spontaneously when the energy of the products is less than that of the reactants.
-If ΔG is negative = spontaneous
-If ΔG is positive = nonspontaneous
Free energy, Stability, and Equilibrium
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When ΔG is negative, the final state has less free energy than the initial state  the final state is less
likely to change and is more stable
A system rich in free energy has the tendency to change spontaneously to a more stable state, a
state of equilibrium
-Moving toward equilibrium is spontaneous because the ΔG of the reaction is negative
-At equilibrium, the forward and backward reactions are proceeding at the same right and the relative concentrations of products and reactants stays the same
*Equilibrium = equal rates of reaction, but the concentrations do not have to be equal;
the concentrations just stay constant
-Once at equilibrium, a system is at a minimum of free energy and will not spontaneously
change
Free Energy and Metabolism
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Reactions may be either exergonic or endergonic
Exergonic: releases free energy
- ΔG is negative; it’s spontaneous
-downhill
-Example = CELLULAR RESPITATION (C6H12O6 + O2  CO2 + H2O + ATP)
-All kingdoms of life carry out cellular respiration
-It produces or releases energy
Endergonic: absorbs free energy
- ΔG is positive; it’s nonspontaneous
-uphill
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-example: PHOTOSYNTHESIS (CO2 + H2O C6H12O6 + O2)
-Only plants, some bacteria, and some protists carry out photosynthesis
-This process uses chloroplasts
-It uses an input of energy to decrease entropy
Coupled Reaction: exergonic reactions fuel endergonic ones
-In cellular reactions, endergonic reactions are typically coupled with exergonic reactions.
-The exergonic reactions provide the energy to “push” the endergonic reactions “uphill”
-The energy released by an exergonic reaction (–ΔG) is equal to the energy required by the
reverse reaction (+ΔG)
Metabolic disequilibrium is essential to life
-Metabolic reactions are reversible and could reach equilibrium if the cell did not maintain a
steady supply of reactants and siphon off the products (as reactants for new processes or as
waste products to be expelled)
ATP and Cellular Work
A cell performs 3 primary types of work:
1) Mechanical = involves movement
-moving cilia or flagella, contracting muscles, moving chromosomes
2) Transport
-Active or passive transport
3) Chemical
-coupling endergonic reactions with exergonic reactions
Structure of ATP
ATP = adenosine triphosphate
3 phosphates
(=highly negative)
Adenine
(purine)
ATP consists of the nitrogenous base adenine
bonded to the sugar ribose, which is connected
to a chain of three phosphate groups.
Ribose
sugar
Hydrolysis of ATP
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ATP isn’t stored within the cell, but is continually converted.
ATP can be hydrolyzed to ADP (adenine diphosphate) and an inorganic phosphate (Pi)
ATP  ADP + Pi +7.3 kcal/mol
-Energy is a product: the reaction is exergonic
-This equation can be rewritten as:
ATP  ADP + Pi
ΔG = -7.3 kcal/mol
-About 10 million molecules of ATP are consumed/regenerated each second per cell.
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-The ΔG of this reaction in the cell is estimated to be closer to 13 kcal/mol
The system doesn’t reach equilibrium because the product of one reaction (exergonic) becomes the
reactant of the next reaction (endergonic)
-Fuels are continually supplied and wastes are removed.
ATP is the immediate source of cellular energy
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Energy from ATP comes from the high energy 3rd phosphate bond
-The phosphate bonds in ATP are weak and unstable, so they yield a high amount of energy
when broken.
-This instability is the result of the combination of the 3 “crowded” negative charges from the
phosphate groups on the tail of the molecule. The 3 negative charges repel each other.
-This instability results in breakdown and release of energy
ATP energizes other molecules by transferring phosphate groups to them (=phosphorylation)
-Phosphorylation: addition of a phosphate, which raises a molecule’s energy
-This produces a molecule that is more reactive and less stable
-The free energy released from the hydrolysis of ATP is used to transfer phosphate groups
Regeneration of ATP
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A cell regenerates ATP at a phenomenal rate
The formation of ATP from ADP and Pi is endergonic, with a ΔG of +7.3 kcal/mol (in standard
conditions)
-This means that making ATP requires an input of energy
Direct source of energy = sunlight
Indirect source of energy = food
*Glucose by itself isn’t a good source of energy because it packs too much of an energy punch. It
contains more energy than required, and will explode the cell
Cellular respiration (the catabolic processing of glucose and other organic molecules) provides this
energy for the regeneration of ATP
-Plants can also produce ATP using light energy
-Mitochondria convert glucose into ATP in the process of cellular respiration
Enzymes
The Activation Energy Barrier
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Activation energy: additional energy requirement to start a reaction
-Most reactions (even exergonic ones) require an input of energy in order to initiate a chemical
reaction
-It requires energy to break chemical bonds; and energy is released when bonds form
-The activation energy allows reactants to reach the unstable transition state, where bonds are
likely to break and from which the reaction can proceed
-This is the peak of the graph (see below)
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-The EA (activation energy) barrier is essential to life because it prevents the energy-rich
macromolecules of the cell from decomposing spontaneously
-For metabolism to proceed, the EA must be reached
The rate of the reaction is dependent upon the amount of activation energy required to initiate the
reaction.
Catalysts are chemical agents that speed up rates of reaction but are unchanged by the reaction.
-They do not affect the net energy released; they only lower the activation energy barrier
-They are not consumed by the reaction.
Enzymes are biological catalysts and function by lowering the activation energies so that reactions
can occur more quickly and metabolism can proceed at cellular temperature
-Example: the enzyme sucrose speeds up hydrolysis of sucrose
*Enzymes do not change the ΔG for a reaction
Potential Energy Diagram
Activation energy
Enzymes lower the activation energy
(=temperature at which the reaction occurs)
Potential
energy
PE of
reactants
ΔH = enthalpy = heat of reaction
PE of products
Time
Overview of Enzymes
1. Most are proteins (at their tertiary structure at least)
2. Reduce activation energy without altering energy of products
3. Speed up rate of reaction – reaction takes less time
4. Not consumed by the reaction
5. Can be re-used again and again
6. Can catalyze both synthesis and decomposition reactions
7. Are very specific: substrate must fit active site of enzyme
8. Names of enzymes often end in –ase
9. May be altered by temperature, pH, salinity, or cofactors
10. Inhibitors reduce or prevent enzyme activity (noncompetitive or competitive)
Catalytic Cycle of Enzyme Action
1. Binding of substrate to active sit of enzyme
-Active site: pockets or clefts in the surface of the enzyme protein
-Enzymes must fit precisely into the active site of the substrate
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*Enzyme specificity depends on the shape of the enzyme (specifically, the shape of its
active site)
-When the substrate binds to the enzyme, it forms the enzyme substrate complex
2. Binding of substrate results in induced fit
-The combination of enzyme and substrate often involves induced fit: when the enzyme’s
shape changes slightly, resulting in an even better fit and enhancing the enzyme’s ability to
catalyze the chemical reaction
a. The enzyme stresses the substance by stretching and bending the chemical bonds
-Enzymes are held to substrate by hydrogen or ionic bonds
b. The enzyme distorts the substrate and reduces the amount of free energy needed to
break bonds
c. The binding of the enzyme to the substrate may create a microenvironment that is
more conducive to a reaction by:
1) Transfer of Hydrogen ions
2) Interaction with acid R groups
d. There is brief covalent bonding between the enzymes
3. Substrate is converted to product while at the active site
4. Enzyme releases degraded substance; active site is available for another molecule
-Enzymes are recyclable: can be re-used again and again
Characteristics of enzyme-mediated reactions
1. Most reactions are reversible.
-Enzymes catalyze both forward and reverse reactions.
-Which reaction is catalyzed is dependent upon the concentration of the substances
present.
-Enzymes catalyze reactions going towards equilibrium
-There is no specific direction to determine which enzymes bind with which substrates.
2. The rate of the reaction is concentration dependent.
-The rate of the reaction is fastest when it first starts because there is a high
concentration of substrates that need to bind with available enzymes
-The rate eventually slows down until it becomes constant as the substrate
concentration decreases. The enzymes have less substrate molecules to react with.
-Reactions may reach the saturation point when all active sites are occupied
Rate of Enzymatic Reactions
Constant reaction rate: all substrates saturated with enzymes
Increase in reaction rate
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Factors Affecting Enzyme Activity
1. Temperature
-A slight increase in temperature will increase the kinetic energy of molecules  this
increases the rate of the reaction up to a point
-Enzymes have temperature optimums at which they function best
-Too high or too low of a temperature will denature the enzyme (=alter the shape of its
active site)
2. pH
-Enzymes have an optimum pH
-pH levels above or below the optimum will denature the enzyme
-example: pepsin works in the low pH of the stomach (2-3) while trypsin works at a pH of 7-8
in the small intestine
3. Salinity (salt concentration)
-If the salt concentration is close to zero or really high, the enzyme will denature
-Enzymes have an optimum at intermediate salt concentrations
4. Presence of cofactors
-Cofactors and coenzymes= nonprotein helpers that help fill in the active site and bind
either permanently or reversibly with enzymes
Cofactors:
Coenzymes
-inorganic
-organic
-metallic elements like iron
-vitamins
5. Enzyme inhibitors
a. Competitive inhibitors – bind to the active site and compete with the substrate
-They block the actual enzyme
-Increasing the concentration of substrate molecules may overcome this type of
inhibition
b. Noncompetitive inhibitors – bind to another part of an enzyme, causing the enzyme to
change shape and making the active site less effective
-Example = allosteric enzymes
Metabolic Control Mechanisms
Biochemical pathways
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Biochemical pathways are a sequence of chemical pathways in which the product of one reaction
becomes the reactant of the next reaction.
-Biochemical pathways are the organizational units of metabolism.
Evolution of biochemical pathways:
1. First organisms – heterotrophs – used organic nutrients of primordial soup
2. Organisms were able to synthesize nutrients from 2 smaller energy rich materials
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3. Once an energy source was depleted, those organisms that could synthesis a replacement
energy source were able to survive
4. Eventually, organisms that were able to synthesize a new substance can produce the same
end product by a complicated series of steps
**This process probably evolved one step at a time over long periods of time
Control of Metabolism
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Control of chemical pathways is achieved by making the enzymes involved in the process
catabolically active or inactive
1. Allosteric regulation = noncompetitive inhibition
-In allosteric regulation, molecules may inhibit or activate enzyme activity when they bind to
a site separate from the active site.
-Many enzymes have an allosteric site: a specific receptor site which is NOT the active site
-Binding of an inhibitor to allosteric site = reinforces the inactive form of the enzyme
-Cooperativity is when the induced-fit binding of a substrate molecule to one subunit
changes the shape so the active sites of all subunits are more active
2. Feedback inhibition
-In feedback inhibition, the end product of a pathway inhibits an enzyme early in the
pathway, preventing the cell from producing an excess of a particular substance
-Metabolic pathways are commonly regulated by feedback inhibition
-Example: cellular respiration is regulated by ATP which inhibits phosphofructokinase
Localization of enzymes
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Enzymes are sequestered in mitochondria according to function
o Different locations have different enzymes and different amounts of those enzymes,
based on the process being carried out at that location and how the enzymes need to
function
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Chapter 9: Cellular Respiration
Catabolic pathways yield energy by oxidizing organic fuels
Catabolic Pathways and Production of ATP
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Fermentation: the partial degradation of sugars to release energy without oxygen
Aerobic respiration: uses oxygen in the breakdown of glucose to yield carbon dioxide and water
and release energy as ATP and heat
*Cellular respiration is referred to as the aerobic process
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Anaerobic respiration: does not use oxygen as a reactant but is a similar process
-Carried out by prokaryotes
Redox Reactions: Oxidation and Reduction
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Oxidation-reduction or redox reactions involve the partial or complete transfer of one or more
electrons from one reactant to another
Oxidation = loss of electrons
-The substance that loses electrons becomes oxidized and acts as a reducing agent (electron
donor) to the substance that gains electrons
Reduction = gain of electrons
-By gaining electrons, a substance acts as an oxidizing agent (electron acceptor) and becomes
reduced
Oxygen strongly attracts electrons and is one of the most powerful oxidizing agents
-As electrons shift toward a more electronegative atom, they give up potential energy
-Chemical energy is released in a redox reaction that relocates electrons closer to oxygen
*Organic molecules with an abundance of hydrogen are rich in “hilltop” electrons that release
their potential energy when they “fall” closer to oxygen
In cellular respiration:
o NAD+ picks up electrons and is reduced to NADH
o Energy from respiration is released as electrons are passed from NADH down an
electron transport chain, a group of carrier molecules located in the inner
mitochondrial membrane. These electrons eventually reach a stable location next to
highly electronegative oxygen, forming a water molecule.
The Cell and Energy
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Free energy is stored as ATP in the 3rd high energy phosphate bond
Activities that require energy:
1) Transport and movement
2) Reproduction and growth
3) Biochemical reaction (e.g. protein synthesis)
ATP can be broken down to produce ADP and an inorganic phosphate. The phosphate can then
phosphorylate and energize another molecule.
For organisms, a direct source of energy is sunlight and an indirect source is food
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Glucose cannot be used as a direct source of energy because it contains more energy than required
and will explode the cell
Instead, glucose must be oxidized to form ATP in the mitochondria of cells
-Mitochondria are similar to chloroplasts: they share an evolutionary history
-Difference between them:
-Chloroplasts make glucose and use energy (photosynthesis)
-Mitochondria break down glucose and produce energy (cellular respiration)
Cristae within the mitochondria = infolded membrane that increases surface area
-Enzymes are embedded here, so it increases the number of enzymes, therefore increasing the
rate of reaction
The circulatory system transports glucose and oxygen to cells
An Overview of Cellular Respiration
C6H12O6 + 6O2  6H2O + 6CO2 + ATP (36–38)
1) Glycolysis – breaks glucose into 2 molecules of pyruvate
-Occurs in cytosol
-NAD+ is reduced to form NADH
2) Krebs Cycle - oxidizes pyruvate into carbon dioxide
-Occurs in mitochondrial matrix (pyruvate enters the mitochondria after glycolysis)
-NAD+ is reduced to form NADH
3) Oxidative Phosphorylation
1. Electron transport = NADH and FADH2 pass electrons to the electron transport
chain, from which they combine with hydrogen ions and oxygen to form water
2. Chemiosmosis = The energy released through this electron transport chain of redox
reactions and diffusion of H+ ions is used to synthesize ATP
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 Purpose of cellular respiration = to produce energy in the form of ATP
-36 to 38 molecules of ATP may be generated for each molecule of glucose oxidized to
carbon dioxide
-The reason it varies is because energy might be lost to move pyruvate into
mitochondria
-About 10% of this ATP is produced by substrate-level phosphorylation (SLP) – you SLAP a
phosphate onto ADP
-NADH = 3 ATPs
-FADH2 = 2 ATPs
-All organisms carry out cellular respiration
Glycolysis
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All living things carry out glycolysis
-This has led scientists to believe that all living things have a common ancestry
In an overview of glycolysis, one molecule of glucose is decomposed into 2 molecules of pyruvate.
This produces 2 molecules of ATP.
ATP is produced through Substrate Level Phosphorylation (SLP) = phosphate added to ADP
Glycolysis takes place in the cytosol
-Glucose is stored in the body in liver and muscle tissue as glycogen
-The circulatory system transports both glucose and oxygen to cells
-Glucose diffuses into the cell through passive transport: facilitated diffusion with a channel
protein
ATP net gain = 2
-ATP cost = 2
-ATP gain = 4
Glycolysis I (energy investment phase)
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In the first step of glycolysis, glucose is phosphorylated to form glucose 6-phosphate.
-Glucose picks up a phosphate group from ATP
-It’s called glucose 6-phosphate because the phosphate is attached to carbon 6
*This added phosphate group confines glucose 6-phosphate within the cell and increases its
energy
Glucose 6-phosphate is converted to fructose 6-phosphate
-They are isomers – their structure is different, but they have the same amount of energy
-Fructose 6-phosphate is highly unstable
Fructose 6-phosphate is phosphorylated by ATP to fructose 1, 6-diphosphate
-Because it’s been phosphorylated, it also gains energy
-This molecule is symmetrical
Fructose 1, 6-diphosphate is cleaved into 2 3-carbon sugars one ketone sugar, one aldehyde sugar
*Of the 2 molecules formed, both are eventually converted to only one of the sugars
-This is due to Le Chatalier’s Principle: the forward reaction is favored
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-At first, concentrations are the same
-One of the sugars is used up in reactions, so the forward reaction is favored:
the other sugar is converted to make more of the other sugar for the reactions
 End of glycolysis 1: There are 2 3-carbon sugars produced
-2 ATPs have been added/invested  the reaction so far is endergonic
-Glucose has been phosphorylated and gained energy
Glycolysis II (energy payoff phase)
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The role of NAD+ is a high energy electron carrier
-NAD+ (nicoteneadenine dinucleotide) picks up electrons and is converted to NADH
-NADH can also lose electrons and change back to NAD+
When NAD+ accepts an electron and a hydrogen ion from PGAL, it is reduced and forms NADH
Oxidation = lose electrons
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*NADH  NAD+
Reduction = gain electrons
*NAD+  NADH
Remember this by: LEO the lion says GER
The sugar is converted to another molecule, losing energy in the process
-This energy went to reduce NAD+ to NADH (reduction absorbs energy)
-An inorganic phosphate from in the cell is added
In the process of forming and cleaving molecules, 2 ATPs are produced through SLP
-2 molecules of ADP are phosphorylated to form 2 ATP molecules
*Get back 2 ATPs – energy spending is even now
A molecule (called PEP) loses a phosphate  this phosphate phosphorylates ADPs to form ATP once
the bond holding the phosphate is weakened (It does this 2x because there’s 2 PEP molecules for
every 1 glucose)
 The final product of glycolysis is 2 molecules of pyruvate
-The pyruvic acid molecules from glycolysis will move into the mitochondria
 Enzymes catalyze each step of glycolysis:
o Dehydrogenase = takes off H and reduces NAD+
o Other enzymes cleave the 6-carbon sugar and rearrange atoms in substrate molecules
Glycolysis
2 NAD+ is reduced to form 2 NADH (= higher energy)
Uses 2 ATPs
Glucose
(6 – C)
4 ATPs produced by SLP
2 Pyruvate
2 (3 – C)
Net gain = 2 ATP
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Conversion of Pyruvate to Acetyl CoA
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At the end of glycolysis, the 2 pyruvate molecules are in the cytosol
First: the 3-carbon pyruvate moves into the matrix of the mitochondria through active transport
-In the process of moving from one location to another, the 3-carbon pyruvate molecule loses a
carbon and is converted into the 2-carbon Acetyl
-CO2 and NADH are produced
-Anytime carbon is lost, it’s lost in the form of CO2
-NAD+ is reduced to form NADH
The 2-carbon acetate molecule binds to a molecular complex called coenzyme A. The resulting
compound is called acetyl CoA.
-This compound is present within the matrix of the mitochondria of cell.
Krebs Cycle/ Citric Acid Cycle
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The Krebs Cycle occurs in the matrix of the mitochondria
**It is important to remember that for every one molecule of glucose, the Krebs cycle “turns” 2
times
1. The 2 carbon acetyl combines with a 4 carbon molecule to form the 6 carbon product,
citrate/citric acid.
2. Citrate is converted to its 6-carbon isomer
3. The 6-carbon citrate isomer is converted to a 5-carbon molecule.
-The carbon is lost as a molecule of CO2
-NAD+ is reduced to form NADH
4. The 5 carbon molecule is converted to a 4 carbon molecule
-Loses another CO2 molecule
-NAD+ is reduced to a 2nd NADH, a high energy electron carrier
5. The 4 carbon molecule is converted into another 4-carbon molecule
-CoA is displaced by a phosphate group and is released
-An inorganic phosphate is added to GDP, forming GTP, which generates ATP
-The inorganic phosphate from GTP is added to ADP
*ADP is phosphorylated to form ATP though SLP
6. The 4 carbon molecule is converted into another 4-carbon molecule
-FADH is reduced to form FADH2
-FADH2 is also a high energy electron carrier (but less than NADH)
7. The 4 carbon molecule is converted into another 4-carbon molecule
-NAD+ is reduced to form NADH
8. The original 4-carbon molecule (that combined with acetyl CoA to form citrate) is regenerated.
 In the process (for 1 glucose=2 turns of the Krebs cycle), 2 ADP are phosphorylated to form 2 ATP.
NAD+ is reduced to form 6 NADH and FADH+ is reduced to form 2 FADH2. 2 CO2 are produced when
carbon is lost.
-Oxygen is the one substance that has not been used yet
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Oxidative Phosphorylation
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Takes place between the matrix and inner mitochondrial membrane (2nd membrane)
-The infolded membrane (=cristae) creates more surface area, which allows this process to
occur more often and more quickly
-Thousands of electron transport chains are embedded in the cristae (infoldings) of the inner
mitochondrial membrane
2 Parts of Oxidative phosphorylation:
1) Electron transport system = electron transport and pumping of protons (H+) which
create an H+ gradient across the membrane
o NADH and FADH2 are high energy electron carriers  they drop off electrons
 NADH and FADH2 are oxidized because they’re losing electrons as they drop
electrons off at electron carrier proteins
 NAD+ and FADH are continually recycled: drop off electrons and come back to
get more (shift between reduced and oxidized states)
o Ubiquinone (Q or CoQ) and cytochrome C are two proteins that carry electrons
 They are found in all mitochondrial membranes
o Electrons move to proteins of greater electron affinity
 Electron affinity = attraction for electrons
 NADH and FADH2 carry electrons from one electron carrier protein to the next
 Each protein decreases in energy and increases in electron affinity
o This lost energy goes to pump hydrogen ions across the membrane  creates a gradient
of H+ across the membrane
o Oxygen = “Final electron acceptor”
 Oxygen has the highest electron affinity  accepts electrons from NADH
 Oxygen diffuses into the mitochondria and combines with H+ to form water
2)
Chemiosmosis = ATP synthesis powered by the diffusion of H+ back across the membrane
-H+ diffuse back through the membrane, from high to low (passive transport)
-H+ diffuse through the enzyme ATP synthase
-ATP synthase uses the energy of the H+ gradient to allow ADP to be phosphorylated to
form ATP
-Chemiosmosis is an energy-coupling mechanism that uses energy stored in the form of
an H+ gradient across a membrane to drive cellular work
The H+ Gradient
I.
II.
III.
In mitochondria: endergonic redox reactions produce the H+ gradient that drives the
synthesis of ATP
In chloroplasts: light energy is used to create the proton-motive force used to make ATP
by Chemiosmosis, instead of an H+ gradient
In prokaryotes: H+ gradients are used to transport molecules, make ATP, and rotate
flagella
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Here is the picture we looked at in class:
Tallying Up the Total
Glycolysis
Pyruvate 
Acetyl CoA
Krebs
Cycle
ETS (electron
transport system)
Total
Total energy
CO2
0
2
4
0
6
None
NADH
2
2
6
0
10
10 x3 = 30 ATP
FADH2
0
0
2
0
2
2 x2 = 2 ATP
ATP (by SLP)
2
0
2
4
4 ATP
38 ATPs
produced
Fermentation
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Fermentation and anaerobic respiration enable cells to produce ATP without oxygen
Anaerobic respiration: its electron transport chain doesn’t use oxygen as the final electron
acceptor (some use sulfate for example)
Fermentation consists of glycolysis and reactions that regenerate NAD+, which can be reused by
glycolysis
-Doesn’t use an electron transport chain: oxidation of glucose in glycolysis produce a net
of 2 ATP by SLP and NADH is recycled to NAD+ by transfer of electrons
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2 types of fermentation:
1) Alcohol fermentation =pyruvate is converted to ethanol in 2 steps, with the 1st releasing
CO2
*This is for bacteria  Bacteria only carry out glycolysis
-Produces 2 ATP which is okay for tiny bacteria
-Bacteria can survive with such little energy because they’re small, single-celled,
have no organelles, and no transport -recycles NADH
-Alcohol fermentation by yeast is used in brewing, winemaking, and baking
-Obligate anaerobes = poisoned by O2 and need fermentation or anaerobic respiration
to survive
-Obligate aerobes = need O2 to survive and need cellular respiration
-Facultative anaerobes = can survive using fermentation or cellular respiration
2) Lactic acid fermentation = pyruvate is reduced by NADH, forming lactic acid (=lactate) as
an end product, with no release of CO2
-Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt
-Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce
Comparing Fermentation to Cellular Respiration
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Both use glycolysis with NAD+ as the oxidizing agent to convert glucose to pyruvate
To oxidize NADH back to NAD+:
-Fermentation uses pyruvate as the final electron acceptor
-Cellular respiration uses oxygen as the final electron acceptor
Feedback Inhibition and Cellular Respiration
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In feedback inhibition, the end product of a pathway inhibits an enzyme early in the pathway,
preventing the cell from producing an excess of a particular substance
o The supply of ATP in the cell regulates respiration
ATP (the end product of cellular respiration) acts as an inhibitor to the enzyme
phosphofructokinase:
-When there’s an excess of ATP, ATP turns off the process of generating ATP  this slows down
or stops the process
-The process will turn itself back on when its demand for ATP is greater (AMP acts as an
activator to phosphofructokinase)
Poisons and Cellular Respiration
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Poisons block the electron transport chain
o For example, Cyanide binds to an electron acceptor in the membrane prevents electrons
from being carried  no H+ gradient is generated  blocks ATP synthesis
-This is why poisons kill you fast: they literally starve an organism’s cells of energy
Other poisons inhibit the enzyme protein ATP synthase
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