Post on 03-Jan-2016
description
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 9 – Cellular Respiration
• Overview: Life Is Work
• Living cells
– Require transfusions of energy from outside sources to perform their many tasks
• Assemble polymers
• Pump substances against the membrane
• Move
• Reproduce
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cellular Respiration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Basics of Respiration
Biologists define respiration as the aerobic harvesting of energy from food molecules by cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
– Cells break down complex organic molecules (rich in potential energy) to simpler waste products (low in potential energy)
• To get energy to do work
• Rest is given off as heat
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cells do this in two ways:
1) Fermentation
2) Cellular respiration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1) One catabolic process, fermentation
– Is a partial degradation of sugars that occurs without oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2) Cellular respiration
– Most prevalent and efficient catabolic pathway
– Consumes oxygen and organic molecules such as glucose
– Yields more ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The equation for the reaction of cellular respiration:
C6H12O6 + 6O2 6CO2 + 6H2O + Energy(ATP &
Heat)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is exergonic
– But catabolic pathways don’t do work directly
• Just release energy so work can be done
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Redox Reactions: Oxidation and Reduction
• Catabolic pathways yield energy
– Due to the transfer of electrons
– When 1 or more electrons transfers from one reactant to another the process is called oxidation reduction reaction or redox for short
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Principle of Redox
• Oxidation – loss of an electron
– The substance that gives up its electron is the reducing agent
• Reduction the gain of an electron
– The substance that gains the electron is the oxidizing agent
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Examples of redox reactions
Na + Cl Na+ + Cl–
becomes oxidized(loses electron)
Reducing agent
becomes reduced(gains electron)
Oxidizing agent
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Specifically in cellular respiration:
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
becomes oxidized
becomes reduced
• Glucose is oxidized and oxygen is reduced
• Electrons lose potential energy and energy is released
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
To Sum Up
• Remember an electron loses potential energy when it shifts from a less electronegative atom to a more electronegative atom (oxygen is very electronegative)
• So by oxidizing glucose, respiration frees stored energy (in glucose) and makes it available for work (as ATP)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
• Cellular respiration
– Oxidizes glucose in a series of steps
• Because energy can’t be released all at once and still be useful
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest
• Glucose is broken down in a series of steps with the help of enzymes
– First an electron is taken away from a glucose molecule. But a proton goes with the electron, so in effect a Hydrogen atom was removed
– Second it is picked up by a coenzyme NAD+ which will act as an oxidizing agent
• NAD+ is reduced to NADH
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest
– Second it is picked up by a coenzyme NAD+ which will act as an oxidizing agent
• NAD+ is reduced to NADH
• Electrons lose little potential energy going from food to NAD+
• NADH molecule now represents stored energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest
– Third NADH will release their electrons down a series of reactions with oxygen being the final electron acceptor (or receptor)
• This is known as the Electron Transport Chain and uses the energy from the electron transfer to form ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
To Sum Up:
• The electrons removed from food by NAD+ fall down an energy gradient in the ETC to a far more stable location in the electronegative oxygen atom
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Stages of Cellular Respiration: A Preview
– Glycolysis
– The citric acid cycle
– Oxidative phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The first two stages are catabolic pathways that decompose glucose
1) Glycolysis
– Occurs in the cytosol
– Breaks down glucose into two molecules of pyruvate
2) The citric acid cycle
– Occurs in the mitochondrial matrix
– Completes the breakdown of glucose
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Remember, why do we do this?
• Goal of cellular respiration is ATP production
1) Oxidative phosphorylation - redox rxns of the ETC
2) Substrate level phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Substrate level phosphorylation
– ATP is formed directly
• Enzymes transfer a phosphate group from a substrate molecule to an ADP (adenosine diphosphate)
– Generates ATP directly
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Both glycolysis and the citric acid cycle
– Can generate ATP by substrate-level phosphorylation
Figure 9.7
Enzyme Enzyme
ATP
ADP
Product
SubstrateP
+
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of cellular respiration
Figure 9.6
Electronscarried
via NADH
GlycolsisGlucos
ePyruvate
ATP
Substrate-levelphosphorylation
Electrons carried via NADH and
FADH2
Citric acid cycle
Oxidativephosphorylation:
electron transport and
chemiosmosis
ATPATP
Substrate-levelphosphorylation
Oxidativephosphorylation
MitochondrionCytosol
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glycolysis
• Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate
• Glycolysis
– Breaks down 1 glucose into 2 pyruvate
– Occurs in the cytoplasm of the cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis consists of two major phases
– Energy investment phase
– Energy payoff phase
Glycolysis Citricacidcycle
Oxidativephosphorylation
ATP ATP ATP
2 ATP
4 ATP
used
formed
Glucose
2 ATP + 2 P
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H +
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Energy investment phase
Energy payoff phase
Glucose 2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H +
2 NADH
+ 2 H+
Figure 9.8
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A closer look at the energy investment phase
– Be thinking:
• What do I start with?
• What do I add in to this?
• What do I get out of this?
• Where does this occur?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A closer look at the energy payoff phase
– Be thinking:
• What do I start with?
• What do I add in to this?
• What do I get out of this?
• Where does this occur?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Citric Acid Cycle
• Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules
• The citric acid cycle
– Takes place in the matrix of the mitochondrion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Before the citric acid cycle can begin:
– Pyruvate must first be converted to acetyl CoA, which links glycolysis to the citric acid cycleCYTOSOL MITOCHONDRION
NADH + H+NAD+
2
31
CO2 Coenzyme APyruvate
Acetyle CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
This only happens if oxygen is present!
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1) The carboxyl group is removed (it is fully oxidized so it has little chemical energy left)
– First step where CO2 is releasedCYTOSOL MITOCHONDRION
NADH + H+NAD+
2
31
CO2 Coenzyme APyruvate
Acetyle CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2) Electrons are removed and transferred to NAD+ which stores them as NADH
CYTOSOL MITOCHONDRION
NADH + H+NAD+
2
31
CO2 Coenzyme APyruvate
Acetyle CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3) Coenzyme A attaches via an unstable bond, so compound is now highly reactive
CYTOSOL MITOCHONDRION
NADH + H+NAD+
2
31
CO2 Coenzyme APyruvate
Acetyle CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of the citric acid cycle
ATP
2 CO2
3 NAD+
3 NADH
+ 3 H+
ADP + P i
FAD
FADH2
Citricacidcycle
CoA
CoA
Acetyle CoA
NADH+ 3 H+
CoA
CO2
Pyruvate(from glycolysis,2 molecules per glucose)
ATP ATP ATP
Glycolysis Citricacidcycle
Oxidativephosphorylation
Figure 9.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A closer look at the citric acid cycle
– Be thinking:
• What do I start with?
• What do I add in to this?
• What do I get out of this?
• Where does this occur?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 9.12
Acetyl CoA
NADH
Oxaloacetate
CitrateMalate
Fumarate
SuccinateSuccinyl
CoA
-Ketoglutarate
Isocitrate
Citricacidcycle
S CoA
CoA SH
NADH
NADH
FADH2
FAD
GTP GDP
NAD+
ADP
P i
NAD+
CO2
CO2
CoA SH
CoA SH
CoAS
H2O
+ H+
+ H+ H2O
C
CH3
O
O C COO–
CH2
COO–
COO–
CH2
HO C COO–
CH2
COO–
COO–
COO–
CH2
HC COO–
HO CHCOO–
CH
CH2
COO–
HO
COO–
CH
HC
COO–
COO–
CH2
CH2
COO–
COO–
CH2
CH2
C O
COO–
CH2
CH2
C O
COO–
1
2
3
4
5
6
7
8
Glycolysis Oxidativephosphorylation
NAD+
+ H+
ATP
Citricacidcycle
Figure 9.12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidative Phosphorylation . . . ETC
• Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
• So far, only 4 ATP have been made
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Pathway of Electron Transport
• Electron Transport Chain – is a collection of molecules embedded in the inner membrane of the mitochondria
– Most components are proteins
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An NADH molecule begins the process by “dropping off” its electron at the first electron carrier molecule
H2O
O2
NADH
FADH2
FMN
Fe•S Fe•S
Fe•S
O
FAD
Cyt b
Cyt c1Cyt c
Cyt aCyt a3
2 H + + 12
I
II
III
IV
Multiproteincomplexes
0
10
20
30
40
50
Fre
e e
ner
gy
(G)
rela
tive
to O
2 (k
cl/m
ol)
Figure 9.13
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Remember: each component will be reduced when it accepts the electron and oxidized when it passes the electron down to the more electronegative carrier molecule in the chain
H2O
O2
NADH
FADH2
FMN
Fe•S Fe•S
Fe•S
O
FAD
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
2 H + + 12
I
II
III
IV
Multiproteincomplexes
0
10
20
30
40
50
Fre
e e
ner
gy
(G)
rela
tive
to O
2 (k
cl/m
ol)
Figure 9.13
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Finally the electron is passed to oxygen, which is very electronegative.
H2O
O2
NADH
FADH2
FMN
Fe•S Fe•S
Fe•S
O
FAD
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
2 H + + 12
I
II
III
IV
Multiproteincomplexes
0
10
20
30
40
50
Fre
e e
ner
gy
(G)
rela
tive
to O
2 (k
cl/m
ol)
Figure 9.13
The oxygen also picks up 2 H+ ions from the aqueous solution and forms water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• FADH goes through mostly the same processes, except it drops off its electron at a lower point on the ETC
H2O
O2
NADH
FADH2
FMN
Fe•S Fe•S
Fe•S
O
FAD
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
2 H + + 12
I
II
III
IV
Multiproteincomplexes
0
10
20
30
40
50
Fre
e e
ner
gy
(G)
rela
tive
to O
2 (k
cl/m
ol)
Figure 9.13
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
WARNING: The ETC makes no ATP directly!
The ETC releases energy in a step-wise series of reactions. It powers ATP synthesis via oxidative phosphorylation.
But it needs to be coupled with chemiosmosis to actually make ATP.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chemiosmosis: The Energy-Coupling Mechanism
• Inner membrane of mitochondria has many protein complexes called ATP synthase
– ATP synthase – enzyme that makes ATP from ADP and inorganic phosphate
• It uses the energy of an existing gradient to do this.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The existing gradient is the difference in H+ ion concentration on opposite sides of the inner membrane of the mitochondria
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Protein complexof electron carners
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
So what is this process called?
• Chemiosmosis – the process in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work (like the synthesis of ATP)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• It is the job of the ETC to create this H+ ion gradient
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Protein complexof electron carners
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• H+ ions are pumped into the intermembrane space by the ETC
– The H+ ions want to drift back into the matrix
• But they can only come into the matrix easily through ATP synthase channels
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The rushing of H+ ions through ATP synthase acts like water turning a water wheel
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+ H+
H+
P i
+ADP
ATP
A rotor within the membrane spins clockwise whenH+ flows past it down the H+
gradient.
A stator anchoredin the membraneholds the knobstationary.
A rod (for “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob.
Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. MITOCHONDRIAL MATRIXFigure 9.14
Result is that inorganic phosphate can be joined to ADP to make ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
To Sum Up
Chemiosmosis is an energy coupling mechanism that uses energy stored in the form of a H+ gradient across a membrane to drive cellular work
In mitochondria, the energy for gradient formation comes from the exergonic redox reactions of the ETC and ATP synthesis is the work performed by ATP synthase
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Chemiosmosis and the electron transport chain
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Protein complexof electron carners
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• There is a problem though, when we try to account how much ATP is made from glucose (or any organic molecule)
We can not state exactly how many ATP come from each glucose because of 3 reasons . . .
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
1) The ETC and ATP synthase work together, but not 100% in synchronicity
So there isn’t an exact correlation between NADH (or FADH) and ATP production
1 NADH synthesizes 2.5 – 3.3 ATP (
1 FADH synthesizes 1.5 – 2 ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2) The electron shuttle into the mitochondria can vary (either NAD+ or FAD) at the transition stage
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
3) The H+ ion gradient does other things in the mitochondria, it is not just used for the synthesis of ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Bottom Line
• We’ll say there are 38 ATP:
Electron shuttlesspan membrane
CYTOSOL 2 NADH
2 FADH2
2 NADH 6 NADH 2 FADH22 NADH
Glycolysis
Glucose2
Pyruvate
2AcetylCoA
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
MITOCHONDRION
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol
Maximum per glucose:About
36 or 38 ATP
+ 2 ATP + 2 ATP + about 32 or 34 ATP
or
Figure 9.16
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
An interesting note:
• Cellular respiration harvests about 40% of the energy in a glucose molecule
– This is perhaps the most efficient energy conversion known
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
In comparison:
• The most efficient cars only convert about 25% of the energy stored in gas into energy that moves the car
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen
• Cellular respiration
– Relies on oxygen to produce ATP
• In the absence of oxygen
– Cells can still produce ATP through fermentation
– Not as much ATP is made
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis
– Can produce ATP with or without oxygen, in aerobic or anaerobic conditions
– Couples with fermentation – an extension of glycolysis, to produce ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Types of Fermentation
• Fermentation consists of
– Glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Type 1
•In alcohol fermentation
– Pyruvate is converted to ethanol in two steps, one of which releases CO2
– The second regenerates NAD+ so glycolysis can continue
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Type 2
•During lactic acid fermentation
– Pyruvate is reduced directly to NADH to form lactate as a waste product
– No CO2 is produced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other organic fuels to pyruvate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fermentation and Cellular Respiration Contrasted
• Fermentation and cellular respiration
– Differ in their final electron acceptor
• Cellular respiration
– Produces more ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 presentFermentation
O2 present Cellular respiration
Ethanolor
lactate
Acetyl CoA
MITOCHONDRION
Citricacidcycle
Figure 9.18
Some organisms can produce ATP using either cellular respiration or fermentation. They are called facultative anaerobes.
Ex: our muscle cells
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Versatility of Catabolism
• Catabolic pathways
– Funnel electrons from many kinds of organic molecules into cellular respiration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The catabolism of various molecules from food
Amino acids
Sugars Glycerol Fattyacids
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citricacidcycle
Oxidativephosphorylation
FatsProteins Carbohydrates
Figure 9.19
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Biosynthesis (Anabolic Pathways)
• The body
– Uses small molecules to build other substances
• These small molecules
– May come directly from food or through glycolysis or the citric acid cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Regulation of Cellular Respiration via Feedback Mechanisms
• Cellular respiration
– Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle