Download Chapter 8

Cellular Respiration:
Harvesting Chemical Energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Contexts of Respiration
– Breathing provides for the exchange of O2
and CO2 between an organism and its
environment.
O2
A summary
of cellular
respiration
http://www.youtu
be.com/watch?v
=rGaP9nE8d9k
CO2
1. Breathing: bringing air into and
out of the lungs
Lungs
CO2
Bloodstream
2. External respiration: Exchange of
O2 & CO2 between an organism (blood)
and its environment
O2
3. Internal respiration: Exchange
of O2 & CO2 between the blood &
body tissues
Muscle cells carrying out
4. Cellular Respiration
Glucose + O2
CO2 + H2O + ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• Cellular respiration may be defined as “A
catabolic process that produces ATP when
oxygen (O2) is consumed as a reactant along with
the organic fuel.”
• During cellular respiration, the fuel (such as
glucose) is oxidized and oxygen is reduced:
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain -1
• In cellular respiration, glucose and other organic molecules
are broken down in a series of steps.
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
• Glucose loses electrons (i.e. it gets oxidized).
•
NADH and FADH2 carry these electrons and eventually deliver them to
oxygen to form water 2e- + 2H+ + ½ O2 → H2O
How would these electrons make
the trip from NADH to the oxygen?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidation-Reduction Reactions
Oxidation: Loss
of electrons.
Reduction: Gain
of electrons.
Redox reactions
require both a
donor and an
acceptor of
electrons.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
My friend, oxygen, I want to give you TWO
electrons so you can form water.
Shall I deliver these TWO electrons in one
dangerous and quick step or let them take
the safe steps down?
NADH + H+
My friend NADH, Let your electrons
take the steps down. Slowly, but surely
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-4
2 e– + 2 H+
2 e– + H+
NAD+
H+
NADH
Dehydrogenase
+ 2[H]
(from food)
+
H+
Nicotinamide
(reduced form)
Nicotinamide
(oxidized form)
Electrons from organic compounds,
such as glucose, are usually first
transferred to NAD+, a coenzyme, to
form NADH.
NAD+
+
2e-
+
2H+
↔
- NAD+H+
+ H+
The Stages of Cellular Respiration: A Preview
• Cellular respiration has three stages:
– Glycolysis (breaks down glucose into
two molecules of pyruvate)
– The citric acid cycle (completes the
breakdown of glucose)
– Oxidative phosphorylation (accounts
for most of the ATP synthesis)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
A Simplified model of glycolysis
2
NAD+
2
NADH
+ 2
H+
Glucose
2 Pyruvate
2 ADP
+2
P
2
ATP
http://www.youtube.com/watch?v=3GTjQTqUuOw
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Intermediate Stage Between Glycolysis and the
Citric Acid Cycle
MITOCHONDRION
CYTOSOL
NAD+
NADH
+ H+
Acetyl Co A
Pyruvate
Transport protein
CO2
Coenzyme A
The Intermediate Stage Between Glycolysis and the
Citric Acid Cycle
NAD+
NADH
+ H+
CoA
Pyruvate
Acetyl CoA
(acetyl coenzyme A)
CO2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Coenzyme A
The Citric Acid Cycle
• The citric acid cycle, also called the Krebs cycle,
takes place within the mitochondrial matrix
• The cycle oxidizes acetyl CoA (the organic fuel
derived from pyruvate), generating the following
per one turn of the cycle:
– 1 ATP
– 3 NADH
– 1 FADH2
– 2 CO2.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Mitochondrion
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Mitochondrial
DNA
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Glycolysis and the Citric Acid Cycle
http://www.youtube.com/watch?v=-cDFYXc9Wko
Glycolysis
Pyruvate
Glucose
Cytosol
Citric
acid
cycle
Mitochondrion
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
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
Cellular Respiration—Aerobic Cellular
Respiration: Citric Acid Cycle
What energy molecules are produced in
breaking down one molecule of glucose in
the citric acid cycle?
Two “turns” of the citric acid cycle produce:
2 ATP
6 NADH
2 FADH2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2- Oxidative Phosphorylation
• One glucose molecule would yield a maximum of
32 ATP via cellular respiration.
• Glycolysis yields ___ ATP by substrate-level
phosphorylation.
• The citric acid cycle yields ___ ATP by substratelevel phosphorylation.
• The rest of 32 ATP ( ____ ATP) will be formed by
oxidative phosphorylation.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2- Oxidative Phosphorylation
•
http://www.wiley.com/legacy/college/boyer/0470003790/animations/ele
ctron_transport/electron_transport.swf
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-6_3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Oxidative Phosphorylation:
1- The Electron Transport Chain
3
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4
Oxidative Phosphorylation:
1- The Electron Transport Chain
• 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
water.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidative Phosphorylation: 1- Electron Transport
Chain / Generation of Proton Motive Force
3
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4
Oxidative Phosphorylation: 2- Chemiosmosis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidative Phosphorylation (Summary):
1- The electron transport chain 2- Chemiosmosis
Glycolysis
Citric
acid
cycle
ATP
ATP
Inner
mitochondrial
membrane
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP
H+
H+
H+
H+
Intermembrane
space
Cyt c
Protein complex
of electron
carriers
Q
IV
III
I
ATP
synthase
II
Inner
mitochondrial
membrane
FADH2
NADH + H+
2H+ + 1/2 O2
H2O
FAD
NAD+
Mitochondrial
matrix
ATP
ADP + P i
(carrying electrons
from food)
H+
Electron transport chain
Electron transport and pumping of protons (H+),
Which create an H+ gradient across the membrane
Oxidative phosphorylation
Chemiosmosis
ATP synthesis powered by the flow
of H+ back across the membrane
Oxidative Phosphorylation (Summary):
1- The electron transport chain 2- Chemiosmosis
Inter-membrane space
Matrix of the mitochondrion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidative Phosphorylation (Summary):
1- The electron transport chain 2- Chemiosmosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glycolysis
NADH
NADH
Intermediate stage
Matrix
NADH
e-
FADH2
Citric
acid
cycle
e-
ATP
1 O
2 2
e-
ADP
+ Pi
H+
ATP synthetase
H2O
H+
H+
H+
H+
H+
H+
H+
H+
Electron carriers
H+ pumps
1
Electrons are transferred from NADH and
FADH2 through a series of electron carriers
within the cristae. O2 is the final electron
acceptor.
2
Energy of electrons “falling” is used to move
H+ up its concentration gradient from the
matrix to the outer compartment.
3 ATP synthetase harnesses the kinetic energy
of the H+ “falling” down its concentration
gradient to bond ADP and Pi to form ATP.
http://www.youtube.com/watch?v=kN5MtqAB_Yc&feature=related
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-16
Electron shuttles
span membrane
CYTOSOL
2 NADH
2 NADH
Glycolysis
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2
Pyruvate
2
Acetyl
CoA
6 NADH
Citric
acid
cycle
+ 2 ATP
+ 2 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 26 or 28 ATP
by oxidation phosphorylation, depending
on which shuttle transports electrons
form NADH in cytosol
About
30 or 32 ATP
A summary of cellular respiration
http://www.youtube.com/watch?v=rGaP9nE8d9k