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Figure 7.2
Get used to this picture….
Light
energy
ECOSYSTEM
CO2  H2O
Photosynthesis
in chloroplasts
Cellular respiration
in mitochondria
ATP
Heat
energy
© 2014 Pearson Education, Inc.
Organic
 O2
molecules
ATP powers
most cellular work
Key points you need to take away from this unit
1. Mitochondria
• Mitochondria have a double membrane that allows
compartmentalization within the mitochondria and is
important to its function
• The outer membrane is smooth, but the inner
membrane is highly convoluted, forming folds called
cristae
• Cristae contain enzymes important to ATP
production; cristae also increase the surface area for
ATP production
© 2014 Pearson Education, Inc.
Key points you need to take away from this unit
1. Glycolysis/Citric Acid Cycle
• Glycolysis rearranges the bonds in glucose
molecules, releasing free energy to form ATP from
ADP and inorganic phosphate, and resulting in the
production of pyruvate
• Pyruvate is transported from the cytoplasm to the
mitochondrion, where further oxidation occurs.
• In the Krebs cycle, CO2 is released from organic
intermediates ATP is synthesized from ADP and
inorganic phosphate via substrate level
phosphorylation and electrons are captured by
coenzymes
• Electrons that are extracted in the series of Krebs
cycle reaction are carried by NADH and FADH2 to
the electron transport chain
© 2014 Pearson Education, Inc.
Key points you need to take away from this unit
1.Oxidative phosphorylation
•
•
•
•
•
Electron transport chain reactions occur in chloroplasts,
mitochondria, and prokaryotic plasma membranes
In cellular respiration, electrons delivered by NADH and FADH2
are passed to a series of electron acceptors as they move
toward the terminal electron acceptor, oxygen.
The passage of e- is accompanied by the formation of a H+
gradient across the inner mitochondrial membrane, with the
membrane separating a region of high [H+] from a region of low
[H+]. In prokaryotes, the passage of e- is accompanied by the
outward movement of H+ across the plasma membrane
The flow of H+ back through the membrane-bound ATP
synthase by chemiosmosis generaties ATP from ADP and
inorganic phosphate.
In cellular respiration, decoupling oxidative phosphorylation
from e- transport is involved with thermoregulation
© 2014 Pearson Education, Inc.
Where we started…..
• Energy flows through nature in the form of chemical energy, which is
stored in bonds, especially C-C, C-H
• Mitochondria are the site of energy production in eukaryotic cells
• Compounds can be oxidized or reduced, in respiration, fuels (glucose)
are oxidized while O2 is reduced
• Respiration has three main steps: Glycolysis, Citric Acid Cyle, and
Oxidative Phosphorylation (ETC)
© 2014 Pearson Education, Inc.
From last time…..
• Glycolysis is the breakdown of glucose, takes place in the cytoplasm,
and occurs whether or not O2 is available
• There are 2 phases of glycolysis: energy investment, energy payoff
• It takes 2 ATP to get glycolysis going, but the pathway yields 4 ATP,
leading to a net of 2 ATP
• NAD+ is reduced to NADH which shuttles e- to the ETC
• Pyruvate enters the mitochondria by diffusion through channel
proteins, and is oxidized into CO2 and acetyl-CoA which is used in the
Citric Acid cycle
Ready?
© 2014 Pearson Education, Inc.
 The citric acid cycle, also called the Krebs cycle,
completes the breakdown of pyruvate to CO2
 The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2
per turn
© 2014 Pearson Education, Inc.
Figure 7.10
Pyruvate
CYTOSOL
(from glycolysis,
2 molecules per glucose)
• The citric acid cycle, also
called the Krebs cycle,
completes the breakdown of
pyruvate to CO2
CO2
NAD
CoA
NADH
 H
Acetyl CoA
MITOCHONDRION
CoA
• The cycle oxidizes organic fuel
derived from pyruvate,
generating:
– 1 ATP
– 3 NADH
– 1 FADH2
per turn, with 2 turns/glucose
CoA
Citric
acid
cycle
3 NAD
FADH2
3 NADH
FAD
 3 H
ADP  P
ATP
© 2014 Pearson Education, Inc.
2 CO2
i
Figure 7.10b
Acetyl CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD
FADH2
3 NADH
FAD
 3 H
ADP  P
ATP
© 2014 Pearson Education, Inc.
i
Figure 7.UN09
Glycolysis
ATP
© 2014 Pearson Education, Inc.
Pyruvate
oxidation
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP
ATP
Figure 7.5
H2  ½ O2

2H
Controlled
release of
energy
Free energy, G
Free energy, G
2 H  2 e−
Explosive
release
ATP
ATP
ATP
2 e−
2
© 2014 Pearson Education, Inc.
½ O2
H
H2O
(a) Uncontrolled reaction
½ O2
H2O
(b) Cellular respiration
The Pathway of Electron Transport
 The electron transport chain is in the inner membrane of the
mitochondrion
 Most of the chain’s components are proteins, which exist in
multiprotein complexes
 Some of these proteins are “cytochromes” and contain Fe
atoms
 The carriers alternate reduced and oxidized states as they
accept and donate electrons
 Electrons drop in free energy as they go down the chain and
are finally passed to O2, forming H2O
 In prokaryotes, this process takes place in the plasma
membrane (this is important)
© 2014 Pearson Education, Inc.
Figure 7.14
Here’s a closer look
Intermembrane space
H
H
H
Protein
complex
of electron
carriers
H
Cyt c
IV
Q
Glycolysis
&
Krebs cycle
III
I
NADH
II
FADH2 FAD
2 H  ½ O2
ATP
synthase
H2O
NAD
ADP  P
(carrying electrons
from food)
H
1 Electron transport chain
Oxidative phosphorylation
Matrix
© 2014 Pearson Education, Inc.
ATP
i
2 Chemiosmosis
 Electrons are transferred from NADH or FADH2 to
the electron transport chain
 Electrons are passed through a number of proteins
including cytochromes (each with an iron atom)
to O2
 The electron transport chain generates no ATP
directly
 It breaks the large free-energy drop from food to O2
into smaller steps that release energy in manageable
amounts
© 2014 Pearson Education, Inc.
Figure 7.14b
So then, where does the ATP get generated?
•
•
•
•
•
ATPase is an integral
membrane protein
More of a motor than an
enzyme
Allows H+ to pass
through by chemiosmosis
As this happens the H+
release free energy (ie.
exergonic) which is used
to do work – make ATP
This gradient is called the
proton-motive force due
to its ability to do work
© 2014 Pearson Education, Inc.
H
ATP
synthase
ADP  P
ATP
i
H
2 Chemiosmosis
Video: ATP Synthase 3-D Side View
Video: ATP Synthase 3-D Top View
© 2014 Pearson Education, Inc.
Figure 7.15
So, this is the forest, and the trees
Electron shuttles
span membrane
CYTOSOL
2 NADH
6 NADH
2 NADH
Glycolysis
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2
Pyruvate
Pyruvate
oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
Can you draw this process? Can you explain it?
© 2014 Pearson Education, Inc.
Tally of the ATP
 During cellular respiration, most energy flows in the
following sequence:
glucose  NADH  electron transport chain 
proton-motive force  ATP
 The ETC produces ~26-28 ATP
 Glycolysis = 2 ATP net
 Krebs = 2 ATP (1/turn, 2 turns/glucose)
 Therefore the total generated = 36 (or 34 depending
on who you ask)
© 2014 Pearson Education, Inc.
Concept 7.5: Fermentation and anaerobic
respiration enable cells to produce ATP without
the use of oxygen
 Most cellular respiration requires O2 to produce ATP
 Without O2, the electron transport chain will cease to
operate
 In that case, glycolysis couples with fermentation or
anaerobic respiration to produce ATP
© 2014 Pearson Education, Inc.
 Anaerobic respiration uses an electron transport
chain with a final electron acceptor other than O2, for
example, sulfate
 Fermentation uses substrate-level phosphorylation
instead of an electron transport chain to generate
ATP
© 2014 Pearson Education, Inc.
Types of Fermentation
 Fermentation consists of glycolysis plus reactions
that regenerate NAD, which can be reused by
glycolysis
 Two common types are alcohol fermentation and
lactic acid fermentation
© 2014 Pearson Education, Inc.
 In alcohol fermentation, pyruvate is converted to
ethanol in two steps
 The first step releases CO2 from pyruvate, and the
second step reduces acetaldehyde to ethanol
 Alcohol fermentation by yeast is used in brewing,
winemaking, and baking
Animation: Fermentation Overview
© 2014 Pearson Education, Inc.
Figure 7.16
2 ADP  2 P
Glucose
2 ADP  2 P
2 ATP
i
Glycolysis
Glucose
2 ATP
i
Glycolysis
2 Pyruvate
2 NAD
2 NADH
 2 H
2 NAD
2 CO2
2 NADH
 2 H
2 Pyruvate
2 Ethanol
(a) Alcohol fermentation
© 2014 Pearson Education, Inc.
2 Acetaldehyde
2 Lactate
(b) Lactic acid fermentation
Figure 7.16a
2 ADP  2 P
Glucose
2 ATP
i
Glycolysis
2 Pyruvate
2 NAD
2 Ethanol
(a) Alcohol fermentation
© 2014 Pearson Education, Inc.
2 NADH
 2 H
2 CO2
2 Acetaldehyde
Figure 7.16b
2 ADP  2 P
Glucose
2 ATP
i
Glycolysis
2 NAD
2 NADH
 2 H
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
© 2014 Pearson Education, Inc.
 In lactic acid fermentation, pyruvate is reduced by
NADH, forming 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
© 2014 Pearson Education, Inc.
Comparing Fermentation with Anaerobic and
Aerobic Respiration
 All use glycolysis (net ATP  2) to oxidize glucose
and harvest chemical energy of food
 In all three, NAD is the oxidizing agent that accepts
electrons during glycolysis
 The processes have different final electron acceptors:
an organic molecule (such as pyruvate or
acetaldehyde) in fermentation and O2 in cellular
respiration
 Cellular respiration produces 32 ATP per glucose
molecule; fermentation produces 2 ATP per glucose
molecule
© 2014 Pearson Education, Inc.
 Obligate anaerobes carry out only fermentation or
anaerobic respiration and cannot survive in the
presence of O2
 Yeast and many bacteria are facultative anaerobes,
meaning that they can survive using either
fermentation or cellular respiration
 In a facultative anaerobe, pyruvate is a fork in the
metabolic road that leads to two alternative catabolic
routes
© 2014 Pearson Education, Inc.
Figure 7.17
Glucose
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol,
lactate, or
other products
Acetyl CoA
Citric
acid
cycle
© 2014 Pearson Education, Inc.
The Evolutionary Significance of Glycolysis
 Ancient prokaryotes are thought to have used
glycolysis long before there was oxygen in the
atmosphere
 Very little O2 was available in the atmosphere until
about 2.7 billion years ago, so early prokaryotes
likely used only glycolysis to generate ATP
 Glycolysis is a very ancient process
© 2014 Pearson Education, Inc.
Concept 7.6: Glycolysis and the citric acid cycle
connect to many other metabolic pathways
 Gycolysis and the citric acid cycle are major
intersections to various catabolic and anabolic
pathways
© 2014 Pearson Education, Inc.
The Versatility of Catabolism
 Glycolysis accepts a wide range of carbohydrates
 Proteins must be digested to amino acids and amino
groups must be removed before amino acids can
feed glycolysis or the citric acid cycle
 Fats are digested to glycerol and fatty acids
 Fatty acids are broken down by beta oxidation and
yield acetyl CoA
 An oxidized gram of fat produces more than twice as
much ATP as an oxidized gram of carbohydrate
© 2014 Pearson Education, Inc.
Figure 7.18-5
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
© 2014 Pearson Education, Inc.
Oxidative
phosphorylation
Biosynthesis (Anabolic Pathways)
 The body uses small molecules to build other
substances
 Some of these small molecules come directly from
food; others can be produced during glycolysis or
the citric acid cycle
© 2014 Pearson Education, Inc.
Figure 7.UN11
Inputs
Outputs
Glycolysis
Glucose
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2 Pyruvate  2
ATP
 2 NADH
Figure 7.UN12
Outputs
Inputs
2 Pyruvate
2 Acetyl CoA
2 Oxaloacetate
© 2014 Pearson Education, Inc.
Citric
acid
cycle
2
ATP
6
CO2 2 FADH2
8 NADH
 The citric acid cycle has eight steps, each catalyzed
by a specific enzyme
 The acetyl group of acetyl CoA joins the cycle by
combining with oxaloacetate, forming citrate
 The next seven steps decompose the citrate back to
oxaloacetate, making the process a cycle
 The NADH and FADH2 produced by the cycle relay
electrons extracted from food to the electron
transport chain
© 2014 Pearson Education, Inc.