Cellular Respiration
Chapter 7
• An overview of cellular respiration
High-energy electrons
carried by NADH
GLYCOLYSIS
Glucose
Cytoplasmic
fluid
Figure 6.8
Pyruvic
acid
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
Mitochondrion
• Details of
glycolysis
in the
cytoplasm
Steps 1 – 3 A fuel
molecule is energized,
using ATP.
Glucose
Step
PREPARATORY
PHASE
(energy investment)
1
Glucose-6-phosphate
2
Fructose-6-phosphate
3
Fructose-1,6-diphosphate
Step 4 A six-carbon
intermediate splits into
two three-carbon
intermediates.
4
Glyceraldehyde-3-phosphate
(G3P)
ENERGY PAYOFF
PHASE
5
Step 5 A redox
reaction generates
NADH.
6
Steps 6 – 9 ATP
and pyruvic acid
are produced.
1,3-Diphosphoglyceric acid
(2 molecules)
7
3-Phosphoglyceric acid
(2 molecules)
8
2-Phosphoglyceric acid
(2 molecules)
2-Phosphoglyceric acid
(2 molecules)
9
Figure 6.9B
Pyruvic acid
(2 molecules
per glucose molecule)
What happens if oxygen is not
present?
• Fermentation
– Occurs in the cytosol
– Generate NAD+ for recycling to glycolysis
– No ATP production
– Lactic acid and alcoholic fermentation
Lactic acid fermentation and alcoholic
fermentation
Efficiency of glycolysis and fermentation
When Oxygen is present : Pyruvic acid is chemically groomed
for the Krebs cycle which takes place in the mitochondria
• In the matrix of the mitochondria, each
pyruvic acid molecule is broken down to
form CO2 and a two-carbon acetyl group,
which enters the Krebs cycle
Pyruvic
acid
Acetyl CoA
(acetyl coenzyme A)
CO2
Figure 6.10
When Oxygen is present: The Krebs cycle
completes the oxidation of organic fuel,
generating many NADH and FADH2 molecules
• The Krebs cycle, in
the matrix of the
mitochondria, is a
series of reactions
in which enzymes
strip away electrons
and H+ from each
acetyl group
Figure 6.11A
Acetyl CoA
KREBS
CYCLE
2
CO2
2 carbons enter cycle
Oxaloacetic
acid
1
Citric acid
CO2 leaves cycle
5
KREBS
CYCLE
2
Malic
acid
4
Alpha-ketoglutaric acid
3
CO2 leaves cycle
Succinic
acid
Step 1
Acetyl CoA stokes
the furnace
Figure 6.11B
Steps 2 and 3
NADH, ATP, and CO2 are generated
during redox reactions.
Steps 4 and 5
Redox reactions generate FADH2
and NADH.
Chemiosmosis powers most ATP production in the
inner membrane
• The electrons from NADH and FADH2 travel
down the electron transport chain to oxygen
• Energy released by the electrons is used to
pump H+ into the space between the
mitochondrial membranes
• In chemiosmosis, the H+ ions diffuse back
through the inner membrane through ATP
synthase complexes, which capture the
energy to make ATP
• Chemiosmosis in the mitochondrion inner
membrane
Protein
complex
Intermembrane
space
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
Figure 6.12
ATP SYNTHASE
Connection: Certain poisons interrupt critical events
in cellular respiration
Rotenone
Cyanide,
carbon monoxide
ELECTRON TRANSPORT CHAIN
Figure 6.13
Oligomycin
ATP SYNTHASE
Review: Each molecule of glucose yields
many molecules of ATP
• For each glucose molecule that enters
cellular respiration, chemiosmosis
produces up to 38 ATP molecules
Cytoplasmic
fluid
Mitochondrion
Electron shuttle
across
membranes
GLYCOLYSIS
2
Glucose
Pyruvic
acid
by substrate-level
phosphorylation
2
Acetyl
CoA
used for shuttling electrons
from NADH made in glycolysis
KREBS
CYCLE
by substrate-level
phosphorylation
KREBS
CYCLE
ELECTRON
TRANSPORT CHAIN
AND CHEMIOSMOSIS
by chemiosmotic
phosphorylation
Maximum per glucose:
Figure 6.14
Fermentation is an anaerobic alternative
to aerobic respiration
• Under anaerobic conditions, many kinds of
cells can use glycolysis alone to produce
small amounts of ATP
– But a cell must have a way of replenishing
NAD+