Chapter 9
 Overview of Cellular Respiration
 Inside the Mitochondria
 Fermentation
2
Light
energy
ECOSYSTEM
CO2 + H2O
Photosynthesis
in chloroplasts
Cellular respiration
in mitochondria
ATP
Heat
energy
Organic
O
molecules + 2
ATP powers
most cellular work
 The breakdown of organic molecules is exergonic

Releases HEAT
 Aerobic respiration consumes organic molecules and O2
and yields ATP

Anaerobic respiration is similar to aerobic respiration but consumes compounds
other than O2
 Fermentation is a partial degradation of sugars that occurs
without O2
 Cellular respiration includes BOTH aerobic and anaerobic
respiration but is often used to refer to aerobic respiration
 Although carbohydrates, fats, and proteins are ALL consumed as
fuel, it is helpful to trace cellular respiration with the sugar
glucose
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat)
 Cellular respiration is a cellular process that breaks down nutrient
molecules produced by photosynthesizers with the concomitant
production of ATP.
 It consumes oxygen and produces carbon dioxide (CO2).
 Cellular respiration is an aerobic process.
 It usually involves the complete breakdown of glucose to CO2 and
H2O.
 Energy is extracted from the glucose molecule:
 Released step-wise
 Allows ATP to be produced efficiently
 Oxidation-reduction enzymes include NAD+ and FAD as coenzymes.
6
Oxidation
C6H12O6
+
6O2
6CO2
+
6H2O
+ energy
glucose
Reduction


OIL RIG

Oxidation is losing of electrons

Reduction is gaining of electrons
Electrons are removed from substrates and received
by oxygen, which combines with H+ to become water.

Glucose is oxidized and O2 is reduced.
7
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
becomes oxidized
becomes reduced
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
O2 and glucose enter cells,
which release H2O and CO.
CO2
H2O
intermembrane
space
cristae
Mitochondria use
energy from
glucose to form ATP
from ADP + P .
ADP + P
ATP
© E. & P. Bauer/zefa/Corbis
10
Cellular Respiration
• NAD+ (nicotinamide adenine dinucleotide)
 A coenzyme of oxidation-reduction, it is:
• Oxidized when it gives up electrons (NAD+)
• Reduced when it accepts electrons (NADH)
 Each NAD+ molecule used over and over again
• FAD (flavin adenine dinucleotide)
 Also a coenzyme of oxidation-reduction
 Sometimes used instead of NAD+
 Accepts two electrons and two hydrogen ions (H+) to
become FADH2
11
 Cellular respiration includes Three phases:
1. Glycolysis is the breakdown of glucose into two
molecules of pyruvate.
 It occurs in the cytoplasm.
 ATP is formed.
 It does not utilize oxygen (anaerobic).
2. Pyruvate Oxidation and the Citric Acid Cycle
a.
Pyruvate Oxidation
 Both molecules of pyruvate enter the matrix of the
mitochondria and are oxidized to become acetyl CoA.
 Electron energy is stored in NADH.
 Two carbons are released as CO2 (one from each
pyruvate).
12
2. Pyruvate Oxidation and the Citric Acid Cycle
b. Citric acid cycle
 Occurs in the matrix of the mitochondrion and produces
NADH and FADH2
 A series of reactions, releases 4 carbons as CO2
 Turns twice per glucose molecule (once for each pyruvate)
 Produces two immediate ATP molecules per glucose
molecule
3. Electron transport chain (ETC)
 A series of carriers on the cristae of the mitochondria
 Extracts energy from NADH and FADH2
 Makes NAD+ and FAD
 Produces 32 or 34 molecules of ATP
13
1.
GLYCOLYSIS (color-coded blue)
2.
PYRUVATE OXIDATION and the CITRIC ACID CYCLE
(color-coded orange)
3.
OXIDATIVE PHOSPHORYLATION: Electron transport and
chemiosmosis (color-coded purple)
Electrons
via NADH
GLYCOLYSIS
Glucose
Pyruvate
CYTOSOL
ATP
Substrate-level
MITOCHONDRION
Electrons
via NADH
GLYCOLYSIS
Glucose
Electrons
via NADH
and FADH2
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
ATP
ATP
Substrate-level
Substrate-level
Electrons
via NADH
GLYCOLYSIS
Glucose
Electrons
via NADH
and FADH2
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
ATP
ATP
Substrate-level
Substrate-level
OXIDATIVE
PHOSPHORYLATION
(Electron transport
and chemiosmosis)
ATP
Oxidative
 Overview of Cellular Respiration
 Inside the Mitochondria
 Fermentation
13
 Energy yield from glucose metabolism
 Net yield per glucose
 From glycolysis – 2 ATP
 From citric acid cycle – 2 ATP
 From electron transport chain – 32 or 34 ATP
 Energy content
 Reactant (glucose) 686 kcal
 Energy yield (36 ATP) 263 kcal
 Efficiency is 34%
 Rest of energy from glucose is lost as heat
19
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
 Glycolysis (“sugar splitting”) breaks down glucose into two
molecules of pyruvate
 Glycolysis occurs in the cytoplasm and has two major phases
 Energy investment phase
 Energy payoff phase
 Glycolysis occurs whether or not O2 is present
GLYCOLYSIS
ATP
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
Energy Investment Phase
Glucose
2
ATP used
2 ADP + 2 P
Energy Payoff Phase
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: Energy Investment Phase
Glyceraldehyde
3-phosphate (G3P)
Glucose
Fructose ATP
6-phosphate
ADP
Glucose
6-phosphate
ATP
ADP
Fructose
1,6-bisphosphate
Isomerase
Hexokinase
1
Phosphoglucoisomerase
2
Phosphofructokinase
3
Aldolase
4
5
Dihydroxyacetone
phosphate (DHAP)
GLYCOLYSIS: Energy Payoff Phase
2 NADH
+
2 NAD + 2 H+
2
Triose
phosphate 2
dehydrogenase
Glyceraldehyde
3-phosphate
(G3P)
6
2 ATP
2 ADP
2
Phosphoglycerokinase
1,3-Bisphosphoglycerate
7
2
Phosphoglyceromutase
8
3-Phosphoglycerate
2-Phosphoglycerate
2 H2O
2
Enolase
9
2 ATP
2 ADP
2
Pyruvate
kinase
10
Phosphoenolpyruvate (PEP)
Pyruvate
 Before the citric acid cycle can begin, pyruvate must be
converted to acetyl Coenzyme A (acetyl CoA), which links
glycolysis to the citric acid cycle
 This step is carried out by a multienzyme complex that catalyses three
reactions
 In the presence of O2, pyruvate enters the mitochondrion (in
eukaryotic cells) where the oxidation of glucose is completed
GLYCOLYSIS
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
MITOCHONDRION
CYTOSOL
CO2
Coenzyme A
3
1
2
Pyruvate
Transport protein
NAD+
NADH + H+
Acetyl CoA
 The citric acid cycle, also called the Krebs cycle, completes
the break down of pyruvate to CO2
 The cycle oxidizes organic fuel derived from pyruvate,
generating 1 ATP, 3 NADH, and 1 FADH2 PER TURN
 Because there are 2 pyruvates for each glucose, the Total yield is:
 2 ATP
 6 NADH
 2 FADH2
GLYCOLYSIS
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
ATP
OXIDATIVE
PHOSPHORYLATION
 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
Acetyl CoA
CoA-SH
NADH
+ H+
H2O
1
NAD+
Oxaloacetate
8
2
Malate
H2O
Citrate
Isocitrate
NAD+
CITRIC
ACID
CYCLE
7
Fumarate
CO2
CoA-SH
4
6
NADH
+ H+
3
-Ketoglutarate
CoA-SH
FADH2
5
NAD+
FAD
Succinate
Pi
GTP GDP
ADP
ATP
Succinyl
CoA
NADH
+ H+
CO2
Acetyl CoA
CoA
CoA
CITRIC
ACID
CYCLE
FADH2
2 CO2
3 NAD+
3 NADH
FAD
+ 3 H+
ADP + P i
ATP
 Following glycolysis and the citric acid cycle, NADH and
FADH2 account for most of the energy extracted from food
 These two electron carriers donate electrons to the electron
transport chain, which powers ATP synthesis via oxidative
phosphorylation
GLYCOLYSIS
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
ATP
 The electron transport chain is in the inner membrane
(cristae) of the mitochondrion
 Most of the chain’s components are proteins, which exist in
multiprotein complexes
 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
Protein
complex
of electron
carriers
H+
H+
H+
Cyt c
IV
Q
III
I
II
FADH2 FAD
NADH
(carrying
electrons
from
food)
2 H+ + ½ O 2
NAD+
1
Electron transport chain
H 2O
 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
 Electron transfer in the electron transport chain causes
proteins to pump H+ from the mitochondrial matrix to the
intermembrane space
 H+ then moves back across the membrane, passing through
the protein complex, ATP synthase
 ATP synthase uses the exergonic flow of H+ to drive
phosphorylation of ATP
 This is an example of chemiosmosis, the use of energy in a H+
gradient to drive cellular work
ATP
synthase
H+
ADP + P i
ATP
H+
2
Chemiosmosis
Protein
complex
of electron
carriers
H+
H+
Cyt c
IV
Q
III
I
II
FADH2 FAD
NADH
(carrying
electrons
from
food)
ATP
synthase
H+
H+
2 H+ + ½ O2
NAD+
H2O
ADP + P i
ATP
H+
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis
 Overview of Cellular Respiration
 Inside the Mitochondria
 Fermentation
21
 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 anaerobic respiration or
fermentation to produce ATP
 Fermentation consists of glycolysis plus reactions
that regenerate NAD+, which can be reused by
glycolysis
 Two common types are:
 Alcohol fermentation
 Lactic acid fermentation
 In alcohol fermentation, pyruvate is converted to
ethanol in two steps
 The first step releases CO2
 The second step produces ethanol
 Alcohol fermentation by yeast is used in brewing,
winemaking, and baking
2 ADP + 2 P i
Glucose
2
ATP
GLYCOLYSIS
2 Pyruvate
2 NAD+
2 Ethanol
(a) Alcohol fermentation
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
 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
2 ADP + 2 P i
Glucose
2
ATP
GLYCOLYSIS
2 NAD+
2 Lactate
(b) Lactic acid fermentation
2 NADH
+ 2 H+
2 Pyruvate