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Cellular Respiration
and Fermentation
chapter 9
Catabolic Pathways and
Production of ATP
 Breakdown – exergonic process
 Cellular Respiration  produces energy
 Two fundamental processes
 Substrate-level phosphorylation
 Oxidative phosphorylation -- ~90%
2
Synthesis of ATP – 2 Methods

Substrate-level phosphorylation – Direct
transfer of a phosphate to ADP to make ATP
Enzyme
Enzyme
ADP
P
Substrate
+
Product
ATP
3
Oxidative
phosphorylation
– production
using energy
derived from
transfer of
electrons &
occuring via
chemiosmosis
44
Redox Reactions
 Oxidation-reduction reactions -- redox reactions
 Oxidation – loss of electrons
 Reduction – gain of electrons
becomes oxidized
(loses electron)
Xe-
+
Y
X
+
Ye-
becomes reduced
(gains electron)
 Not reversible!
5
Reducing Agent -- electron donor – gets oxidized!
 Oxidizing Agent -- electron receptor – gets
reduced!
Leo Ger
Loss of Electrons – Oxidation
Gain of Electrons -- Reduction

Oxidation Is Loss; Reduction Is Gain
6
Catabolic Pathways
 Two fundamental “kinds”
 Using organic molecules
 Using inorganic molecules (prokaryotes only)
 Breakdown of organic molecules
 Aerobic – requires oxygen
 Anaerobic (fermentation) – absence of oxygen
7
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cellular Respiration


Both aerobic and anaerobic pathways
Any organic fuel


carbohydrates, fats, and proteins
Generally start with glucose
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy
(ATP + heat)
8
Organic Fuel is Oxidized

ReDox process

During cellular respiration, the fuel (such as glucose) is
oxidized and oxygen is reduced:
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
9
Stepwise Energy Harvest
Glucose -- broken down in a series of steps
 Electron transport chain -- series of steps
instead of one explosive reaction

10
LE 9-5
H2 + 1/2 O2
+
2H
1 /2
O2
1/2
O2
(from food via NADH)
Explosive
release of
heat and light
energy
Free energy, G
Free energy, G
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e–
2
H+
H2O
Uncontrolled reaction
H2O
Cellular respiration
RESPIRATION
C6H12O6 + O2
CO2 + H2O + ENERGY
ATP
686 kcal/mole (180 grams)
12
Glycolysis:
glucose to pyruvate


Glycolysis -- glucose into two molecules of pyruvate
Glycolysis -- occurs in the cytoplasm
Energy investment phase
 Energy payoff phase


Independent reaction
13
LE 9-8
Energy investment phase
Glucose
2 ATP used
2 ADP + 2 P
Glycolysis
Citric
acid
cycle
Oxidative
phosphorylation
Energy payoff phase
ATP
ATP
ATP
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Net
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
Glycolysis


10 steps – specific enzyme
Energy Investment
Glucose to 2 PGAL
 uses ATP


Energy Payoff
PGAL to Pyruvic Acid
 Produces ATP


PGAL/ G3P – phosphoglyceraldehyde or
glyceraldehyde-3-phosphate
15
GLYCOLYSIS
Energy investment phase and splitting
of glucose
Two ATPs invested per glucose
Glucose
2 ATP
3
steps
2 ADP
Fructose-1,6-bisphosphate
P
P
Glyceraldehyde Glyceraldehyde
phosphate
phosphate
(G3P)
(G3P)
P
PGAL
P
16
Fig. 8-3, p. 175
Energy capture phase
Four ATPs and two NADH
produced per glucose
P
P
(G3P)
(G3P)
NAD+
NAD+
NADH
2 ADP
5
steps
NADH
2 ATP
2 ADP
2 ATP
Pyruvate Pyruvate
Net yield per glucose:
Two ATPs and two NADH
17
Fig. 8-3, p. 175
Glycolysis


Is Glycolysis really a part of Aerobic Cellular
Respiration?
Occurs in both Aerobic and Anaerobic
Respiration!
18
Steps of Respiration

3? 4? 5?

Glycolysis
Formation of Acetyl Co-Enzyme A
Krebs Cycle
Electron Transport Chain
Chemiosmosis




19
Glycolysis …. What next?
Glucose
Glycolysis
CYTOSOL
Pyruvate
No O2 present
Fermentation
or Anaerobic
respiration
O2 present -- Aerobic
cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
20
Formation of Acetyl Co-A
MITOCHONDRION
CYTOSOL
NAD+
NADH
+ H+
Acetyl Co A
Pyruvate
CO2
Coenzyme A
Transport protein
21
Formation of Acetyl CoA

1 pyruvate molecule


Acetyl group +
coenzyme A


loses 1 molecule of
carbon dioxide
produce acetyl CoA
Carbon
dioxide
Pyruvate
NAD+
CO2
Coenzyme A
NADH
1 NADH produced
per pyruvate
Acetyl coenzyme A
22
Citric Acid Cycle

Different terms





The citric acid cycle
The Krebs cycle
The Tricarboxylic Acid Cycle
Oxidizes acetyl co-A (fuel derived from pyruvate)
Produced PER Acetyl Co-A




1 ATP
3 NADH
1 FADH2
2 CO2
23
LE 9-11
Pyruvate
(from glycolysis,
2 molecules per
glucose)
CO2
NAD+
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
CoA
NADH
+ H+
Acetyl CoA
CoA
CoA
Citric
acid
cycle
FADH2
2 CO2
3 NAD+
3 NADH
+ 3 H+
FAD
ADP + P i
ATP
ATP
Citric Acid Cycle

1 acetyl CoA enters cycle





2 C enter as acetyl CoA -- 2 leave as CO2
1 acetyl CoA



combines with 4-C oxaloacetate
forms 6-C citrate
Citrate decomposed back to oxaloacetate
transfers H atoms to 3 NAD+ , 1 FAD
1 ATP produced
NADH and FADH2 -- electrons to electron transport
chain
25
Acetyl coenzyme A
Coenzyme A
Citrate
Oxaloacetate
NADH
NAD+
NAD+
CITRIC
ACID
CYCLE
H2O
NADH
CO2
FADH2
5-carbon compound
FAD
GTP
NADH
GDP
4-carbon compound
ADP
CO2
ATP
26
Fig. 8-6, p. 179
Electron Transport Chain
 NADH and FADH2
 account
for most of the energy extracted from food
 Donate electrons to the electron transport chain

Probably the most important step
27
Electron Transport Chain

The electron transport chain generates no ATP


Function -- break the large free-energy drop from
food to O2 releasing energy in manageable amounts



Moves electrons around
Alternating oxidized and reduced states
Maintains pH gradient
Electrons drop in free energy until passed to O2
forming water
28
Electron Transport Chain
Chemiosmosis
4
2
4
29
LE 9-13
NADH
50
Free energy (G) relative to O2 (kcal/mol)
FADH2
40
FMN
I
Multiprotein
complexes
FAD
Fe•S II
Fe•S
Q
III
Cyt b
30
Fe•S
Cyt c1
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylation:
electron transport
and chemiosmosis
IV
Cyt c
Cyt a
Cyt a3
20
10
0
2 H+ + 1/2 O2
H2O
ATP
31
Chemiosmosis
✥
Paul Mitchell theorized in 1961
Nobel Prize in Chemistry in 1978
✥
Energy stored in pH gradient
✥
32
Chemiosmosis: The EnergyCoupling Mechanism

Electron transfer -- proteins pump H+ from
mitochondrial matrix to intermembrane space
-- use of energy in a H+ gradient to
drive cellular work
 Chemiosmosis
H+ through channels in ATP synthase
 ATP synthase uses the exergonic flow to drive
phosphorylation of ATP

33
34
35
CO2
CO2
H2O
36
Electron transport chain
inhibitors


Lack of organic fuel
Cyanide & Carbon monoxide


Rotenone & Amytal


Blocks I
Oligomycin


Blocks IV
Blocks ATP synthase
Antimycin

Blocks III
37
CYANIDE RESISTANT
RESPIRATION
Aerobic respiration is inhibited when the
terminal electron carrier combines with cyanide,
azide or certain other negatively charged ions
This poisons the enzyme and stops electron
transport
38
CYANIDE RESISTANT
RESPIRATION
Some plants, fungi and bacteria
This pathway produces heat rather than ATPs
but is aerobic (i.e., oxygen is the terminal
electron acceptor)
The heat produced by some plants has
important ecological functions.
39
This seems to be
important when
electron transport is
saturated
40
Energy is captured from light by
Philodendron leaves and used
for life processes and growth
When it flowers -- heats to as
high as 46 C (115 F). The heat
protects the flowers from
freezing at night and disperses
compound that attract
pollinators
Light energy —> Heat
41
Skunk Cabbage

Air temp – 5-50 ˚F


Flower temp – 60-72 ˚F


-15-10 ˚C
15-22 ˚C
Some flowers generate
0.4 J heat/second/gram
whereas hummingbirds
generate 0.24 J
heat/second/gram
42
An Accounting of ATP Production
by Cellular Respiration


During cellular respiration -- energy flows in this
sequence:
glucose NADH electron transport chain
 pH gradient ATP
About 40% of the energy is transferred to ATP -making about 38 ATP
43
LE 9-16
Electron shuttles
span membrane
CYTOSOL
2 NADH
Glycolysis
Glucose
2
Pyruvate
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2
Acetyl
CoA
6 NADH
Citric
acid
cycle
+ 2 ATP
+ 2 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
About
36 or 38 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by oxidation phosphorylation, depending
on which shuttle transports electrons
form NADH in cytosol
Fermentation


Facultative anaerobes -- they can survive using either
fermentation or cellular respiration
Pyruvate is a fork in the metabolic road that leads to
two alternative catabolic routes
45
Glucose
Glycolysis
CYTOSOL
Pyruvate
No O2 present
Fermentation
or Anaerobic
respiration
O2 present -- Aerobic
cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
46
Fermentation vs Respiration

Glycolysis -- oxidizes glucose to pyruvate

Different final electron acceptors
 Fermentation
-- an organic molecule (such as
pyruvate)
 Respiration -- O2

Aerobic respiration produces much more ATP
47
Types of Fermentation


Fermentation -- glycolysis plus reactions that
regenerate NAD+, which can be reused by
glycolysis
Two types


alcohol fermentation
lactic acid fermentation
48
Alcohol Fermentation


pyruvate is converted to ethanol in two steps, with
the first releasing CO2
yeast -- brewing, winemaking, and baking
49
LE 9-17a
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 Ethanol
Alcohol fermentation
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
Lactic Acid Fermentation
pyruvate is reduced to NADH, forming lactate
as an end product, with no release of CO2
 fungi and bacteria -- cheese and yogurt
 muscle cells -- lactic acid fermentation

51
LE 9-17b
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
Lactic acid fermentation
Glycolysis and metabolic pathways

Gycolysis and the citric acid cycle are major
intersections to various catabolic and anabolic
pathways
53
LE 9-19
Proteins
Carbohydrates
Amino
acids
Sugars
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Fats
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
The Versatility of Catabolism
funnel electrons into cellular respiration
 wide range of carbohydrates
 amino groups can feed glycolysis or the citric
acid cycle
 fats -- glycerol (used in glycolysis) and fatty
acids (used in generating acetyl CoA)

a
gram of fat > 2X ATP as an oxidized gram of
carbohydrate
55
FIGURE 6.1
56
Biosynthesis (Anabolic Pathways)


The body uses small molecules to build other
substances
These small molecules may come directly from
food, from glycolysis, or from the citric acid cycle
57
58
Regulation of Cellular Respiration:
Feedback Mechanisms
most common mechanism for control
 If ATP concentration drop -- respiration
speeds up
 Enzyme control at strategic points in the
catabolic pathway

59
LE 9-20
Glucose
AMP
Glycolysis
Fructose-6-phosphate
–
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
PHOTORESPIRATION
Some plants increase their use of oxygen when
CO2 gets too low, a process known as
photorespiration.
Photorespiration interferes with photosynthesis
and causes decreased crop yield
61
62
Summary Reaction

Complete oxidation of glucose
C6H12O6 + 6 O2 + 6 H2O →
6 CO2 + 12 H2O + energy (36 to 38 ATP)
[40% of potential energy -> ATP
60% -> wasted (heat)]
63
Summary Reaction

Glycolysis
C6H12O6 + 2 ATP + 2 ADP + 2 Pi + 2 NAD+
→ 2 pyruvate + 4 ATP + 2 NADH + H2O
64
Summary Reaction

Conversion of pyruvate to acetyl CoA
2 pyruvate + 2 coenzyme A + 2 NAD+ →
2 acetyl CoA + 2 CO2 + 2 NADH
65
Summary Reaction

Citric acid cycle
2 acetyl CoA + 6 NAD+ + 2 FAD + 2 ADP
+ 2 Pi + 2 H2O → 4 CO2 + 6 NADH +
2 FADH2 + 2 ATP + 2 CoA
66
Summary Reactions

Hydrogen atoms in Electron Transport
Chain
NADH + 3 ADP + 3 Pi + 12 O2 → NAD+ +
3 ATP + H2O
FADH2 + 2 ADP + 2 Pi + 12 O2 → FAD +
2 ATP + H2O
67
Summary Reaction

Lactate fermentation
C6H12O6 → 2 lactate + 2 ATP + NAD+
Pyruvate → NAD+ + lactate/lactic acid
68
Summary Reaction

Alcohol fermentation
C6H12O6 → 2 CO2 + 2 C2H5OH + 2 ATP + NAD+
Pyruvate -> NAD+ + ethanol + CO2
69
70