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Cellular Respiration II
Glycolysis, Krebs cycle, Electron
transport chain
Food Molecules are Broken
Down in 3 Stages to
Produce ATP
Extracellular/
lysosome
Cytosol
Mitochondria
Cellular Respiration
 Glycolysis
 Krebs
Cycle
 Electron Transport Chain
An overview of cellular respiration
Cellular Respiration
 Glycolysis
 Krebs
Cycle
 Electron Transport Chain
An overview of cellular respiration (Layer 1)
No oxygen here!
Substrate-level phosphorylation
Glycolysis
 Glycolysis
3 phases of glycolysis
Energy investment
1.


Cleavage
2.


Steps 4-5
6 carbon molecule broken into two 3 carbon
molecules of glyceraldehyde-3-phosphate
Energy liberation
3.



Steps 1-3
2 ATP hydrolyzed to create fructose-1,6 bisphosphate
Steps 6-10
Two glyceraldehyde-3-phosphate molecules broken
down into two pyruvate molecules producing 2 NADH
and 4 ATP
Net yield in ATP of 2
10
A closer look at glycolysis: energy investment phase
ENERGY INVESTMENT = 1 ATP!
A closer look at glycolysis: energy investment phase
ENERGY INVESTMENT = 1 ATP!
A closer look at glycolysis: energy payoff phase
ENERGY PAYOFF !=
•2 NADH
•2 ATP
A closer look at glycolysis: energy payoff phase
ENERGY PAYOFF !=
•2 ATP
The energy input and output of glycolysis
Glycolysis costs ____ATPs, but makes
___ATPs; thus it has a net yield of
___ATPs.
33%
1.
2.
3.
33%
33%
3, 6, 3
2, 4, 2
4, 8, 4
1
2
3
All of the glycolysis reactions do not
require oxygen and can take place in
an anaerobic environment.
50%
1.
2.
50%
This is true
This is false
1
2
During glycolysis, ATP is
produced by
1.
2.
3.
Oxidative
phosphorylation
Substrate-level
phosphorylation
Both of the above
33%
1
33%
2
33%
3
Cellular Respiration
 Glycolysis
 Krebs
Cycle
 Electron Transport Chain
An overview of cellular respiration
Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs
cycle
Stage 2: Breakdown of pyruvate to
an acetyl group
 In
eukaryotes, pyruvate in transported to
the mitochondrial matrix
 Broken down by pyruvate dehydrogenase
 Molecule of CO2 removed from each
pyruvate
 Remaining acetyl group attached to CoA
to make acetyl CoA
 1 NADH is made for each pyruvate
22
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
O–
C O
C O
Outer
CH3
membrane
channel
O–
H+/pyruvate
C O
symporter
H+
C O
+ CoA SH
CH3
+
NAD+
Pyruvate
dehydrogenase
S CoA
C O + CO2 + NADH
CH3
Acetyl CoA
23
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glycolysis:
Glucose
2 NADH
2 NADH
6 NADH
Citric
acid
cycle
2 pyruvate
2 CO2
2 CO2
Breakdown of
pyruvate
+2 ATP
2 FADH2
Oxidative
phosphorylation
NADH
CO2
2 CO2
+2 ATP
Citrate
+30–34 ATP
NADH
C C C C C C
C C C C C C
CO2
3
2
C C C C C
4
1
C C C C
Citric acid cycle
O
C C C C
5
Oxaloacetate
H2C C S CoA
Acetyl CoA
8
C C C C
7
NADH
6
C C C C
GTP
C C C C
ATP
FADH2
24
Krebs Cycle
 Krebs
citric acid cycle
A closer look at the Krebs cycle
A closer look at the Krebs cycle
A closer look at the Krebs cycle
Flavin Adenine
Dinucleotide
A closer look at the Krebs cycle
A summary of the Krebs cycle
Per molecule of
glucose X 2!
ENERGY PAYOFF !=
•4 NADH
•FADH2
•2 ATP
The 2 carbons in acetyl–CoA
are eventually used to form —
33%
1.
2.
3.
33%
33%
ATP
Pyruvate
Carbon dioxide
1
2
3
What is the function of the
coenzymes, NADH and FADH2 ?
1.
2.
3.
Charging electrons
to power ATP
synthase
Catalyzing the
formation of
acetyl-CoA
Providing
electrons and H+
to the electron
transport chain
33%
1
33%
2
33%
3
What are the main products of
the Kreb’s cycle?
1.
2.
3.
4.
NADH
FADH2
ATP
All of the above
25%
1
25%
25%
2
3
25%
4
Cellular Respiration
 Glycolysis
 Krebs
Cycle
 Electron Transport Chain
An overview of cellular respiration
The pathway of electron transport
 Collection
of
molecules in the
inner membrane of
the mitochondrion
Stage 4: Oxidative phosphorylation
 High
energy electrons removed from
NADH and FADH2 to make ATP
 Typically requires oxygen
 Oxidative process involves electron
transport chain
 Phosphorylation occurs by ATP synthase
37
Oxidation: ETC

Electron transport chains (ETC)

Group of protein complexes and small organic
molecules embedded in the inner mitochondrial
membrane

Can accept and donate electrons in a linear
manner in a series of redox reactions
 Movement of electrons generates H+
electrochemical gradient/ proton-motive force

Excess of positive charges outside of matrix
38
The pathway of electron transport
 Electrons
pass through a series of
membrane-associated electron carriers
 Flow of electrons along the chain
accomplishes the active transport of
protons (H+) across the inner
mitochondrial membrane
 Protons diffuse back into the mitochondrial
matrix through a proton channel which
couples the diffusion to ATP synthesis
Free-energy change during electron transport
Ubiquinone
Integral membrane
proteins
Cytochrome C
NADH dehydrogenase
NADH
I
H+
H+
H+
KEY
NAD+ + H+
Succinate
reductase
Q
Electron
transport
chain
H+
II
FADH2
FAD + 2
H+ movement
e– movement
Ubiquinone
H+
H+
H- Cytochrome b-c1
III
H+
H+
Cytochrome c
c
H+
H+
2 H+ + ½ O2
IV
Cytochrome oxidase
H+
H+
H2O
H+
Matrix
H+
ATP synthase
H+
ADP + Pi
H+
ATP
Inner mitochondrial
membrane
ATP
synthesis
H+
Intermembrane
space
41
Electron transport
 Animation
of Electron transport in
Mitochondria
Proton diffusion is coupled
to ATP synthesis
Chemiosmosis
Chemiosmosis couples the electron transport chain to ATP synthesis
Chemiosmosis
 Flow
of electrons from one electron carrier
to another is exergonic
 The exergonic reactions drive the
endergonic pump of H+ across the
mitochondrial membrane
 The potential energy of the H+ gradient is
used by ATP synthase to generate ATP
Figure 9.14 ATP synthase, a molecular mill
ATP synthase
 Animation
of ATP synthesis in
Mitochondria
ATP synthesis
 ATP
leaves the mitochondrial membrane
as soon as it is made
 From one molecule of glucose = 38 ATP
molecule (under ideal conditions)
Review: how each molecule of glucose yields many ATP molecules during cellular
respiration
ATP synthase
1.
2.
3.
4.
5.
Is an H+ channel
Is embedded in
the cristae
Spins due to the
flow of H+
Uses rotational
energy to form
ATP
All of the above
20%
1
20%
20%
2
3
20%
4
20%
5
Cyanide inhibits cytochrome
oxidase. Why is this lethal?
1.
2.
3.
NAD+ can no
longer be reduced
to NADH
Electron transport
chain is shut down
Glycolysis is
inhibited
33%
1
33%
2
33%
3
The catabolism of various food molecules
Control of cellular respiration
 Controlled
by feedback mechanisms
 Feedback inhibition

The end product of the anabolic pathway
inhibits the enzyme that catalyzes an early
step of the pathway
 Phosphofructokinase



Allosteric enzyme
Inhibited by ATP
Activated by AMP
– key step
The control of cellular respiration
Anaerobic metabolism
 For
environments that lack oxygen or
during oxygen deficits
 2 strategies


Use substance other than O2 as final electron
acceptor in electron transport chain
Produce ATP only via substrate-level
phosphorylation
55
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Other acceptors

E. coli uses nitrate
(NO3-) under
anaerobic conditions
 Makes ATP via
chemiosmosis even
under aerobic
conditions
KE Y
H+ movement
e– movement
NADH dehydrogenase
NADH
H+
NAD+ +
H+
H+
H+
Ubiquinone
H+
Cytochrome b
Cytoplasm
H+
H+
NO3– + 2 H+
Nitrate reductase
H+
NO2– + H2O
ADP + Pi
ATP
H+
56
H+
ATP synthase
H+
Extracellular
fluid
Fermentation
 Fermentation
keeps ATP production going
when oxygen is unavailable
Fermentation
 Many
organisms can only use O2 as final
electron acceptor
 Make ATP via glycolysis only
 Need to regenerate NAD+ to keep
glycolysis running
 Muscle cells produce lactate
 Yeast make ethanol
 Produces far less ATP
58
Fermentation
 Reaction



pathways
NADH delivers electrons
from glycolysis to organic acceptor molecules
converting NADH back to NAD+
Fermentation
 NAD+

removed from sugars in glycolysis
 ATP

free to accept more electrons
production by glycolysis
continues in absence of oxygen
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2 ADP + 2 Pi
2 ATP
O—
2 ADP + 2 Pi
2 ATP
C O
C O
C O
C O
Glucose
Glycolysis
Glucose
CH3
Glycolysis
CH3
2 pyruvate
2 pyruvate
O—
2 NAD+ + 2 H+
2 NAD+ + 2 H+
2 NADH
C O
H
C OH
CH3
O—
H
2 lactate (secreted from the cell)
H
C OH
C O
2 H+
2 ethanol (secreted from the cell)
(a) Production of lactic acid
(b) Production of ethanol
(weights): © Bill Aron/Photo Edit; (wine barrels): © Jeff Greenberg/The Image Works
61
2 CO2
H
CH3
2 H1
2 NADH
CH3
2 acetaldehyde
Fermentation
Fig. 8-16, p. 173
Cytosol
a. Lactate fermentation
Glycolysis
Glucose
Pyruvate
Lactate
Fig. 8-16a, p. 173
Cytosol
b. Alcoholic fermentation
Glycolysis
Glucose
Pyruvate
Acetaldehyde
Ethyl alcohol
Fig. 8-16b, p. 173