Transcript 6.8-6.10 Citric acid cycle and Oxidative phosphorylation

6.8-6.10 Citric acid cycle and
Oxidative phosphorylation
2014-2015
Student
6.8 Pyruvate is oxidized prior to the citric acid cycle
• This process will not proceed without oxygen
• The pyruvate formed in glycolysis is transported
from the cytoplasm into a mitochondrion where
– the citric acid cycle and
– oxidative phosphorylation will occur.
© 2012 Pearson Education, Inc.
6.8 Pyruvate is oxidized prior to the citric acid cycle
• Two molecules of pyruvate are produced for
each molecule of glucose that enters glycolysis.
• Pyruvate does not enter the citric acid cycle, but
undergoes some chemical grooming in which
– a carboxyl group is removed and given off as CO2,
– the two-carbon compound remaining is oxidized
while a molecule of NAD+ is reduced to NADH,
– coenzyme A joins with the two-carbon group to
form acetyl coenzyme A, abbreviated as acetyl CoA,
and
– acetyl CoA enters the citric acid cycle.
© 2012 Pearson Education, Inc.
Figure 6.8
NAD
NADH
H
2
CoA
Pyruvate
Acetyl coenzyme A
1
CO2
3
Coenzyme A
6.9 The citric acid cycle
• The citric acid cycle
– is also called the Krebs cycle (after the GermanBritish researcher Hans Krebs, who worked out
much of this pathway in the 1930s),
– completes the oxidation of organic molecules, and
– generates many NADH and FADH2 molecules.
© 2012 Pearson Education, Inc.
Figure 6.9A
Acetyl CoA
CoA
CoA
2 CO2
Citric Acid Cycle
3 NAD
FADH2
3 NADH
FAD
3 H
ATP
ADP
P
6.9 The citric acid cycle
• During the citric acid cycle
– the two-carbon group of acetyl CoA is added to a
four-carbon compound, forming citrate,
– citrate is degraded back to the four-carbon
compound,
– two CO2 are released, and
– 1 ATP, 3 NADH, and 1 FADH2 are produced.
© 2012 Pearson Education, Inc.
6.9 The citric acid cycle
• Remember that the citric acid cycle processes
two molecules of acetyl CoA for each initial
glucose.
• Thus, after two turns of the citric acid cycle, the
overall yield per glucose molecule is
– 2 ATP, (useable by the cell)
– 6 NADH, and
– 2 FADH2.
• To the electron transport chain
© 2012 Pearson Education, Inc.
NOTE
• Do NOT get overwhelmed by the names of the
intermediate compound produced by the citric
acid cycle you will NOT be responsible for
knowing their names.
• You may notice:
– Each time a carbon(represented by the gray circles) is
lost from a carbon compounds a CO2 is produced.
– NADNADH2 and FADFADH2 as the molecules in
the citric acid cycle are rearrange and energy is
released as high energy electrons.
Figure 6.9B_s3
Acetyl CoA
CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citrate
NADH
H
NAD
5
NAD
NADH
2
H
Citric Acid Cycle
CO2 leaves cycle
Malate
FADH2
Alpha-ketoglutarate
4
3
FAD
CO2 leaves cycle
NAD
Succinate
ADP
Step 1
Acetyl CoA stokes
the furnace.
P
Steps 2 – 3
ATP
NADH, ATP, and CO2
are generated during redox reactions.
NADH
H
Steps 4 – 5
Further redox reactions generate
FADH2 and more NADH.
6.10 Oxidative phosphorylation
• At this point in Cellular Respiration only 4 ATP
molecules have been produced
– 2 in glycolysis
– 2 in the citric acid cycle
• Oxidative phosphorylation (most ATP is
produced here)
– The energy in NADH2 and FADH2 is converted into
ATP
– involves electron transport and chemiosmosis and
– requires an adequate supply of oxygen.
© 2012 Pearson Education, Inc.
6.10 Oxidative phosphorylation (continued)
• Electrons are released from NADH and FADH2
and travel down the electron transport chain to
O2.
– ETC is a series of proteins embedded in the inner
mitochondrial membrane
• Oxygen “catches” the electrons and picks up H+
to form water.
© 2012 Pearson Education, Inc.
Oxidative phosphorylation (continued)
• Energy released by these redox reactions is
used to pump H+ from the mitochondrial
matrix into the intermembrane space.
• In chemiosmosis, the H+ diffuses back across
the inner membrane through ATP synthase
complexes, driving the synthesis of ATP.
Figure 6.10
H
Intermembrane
space
H
H
H
H Mobile
electron
carriers
Protein
complex
of electron
carriers
H ATP
synthase
IV
I
II
FADH2
Electron
flow
NADH
Mitochondrial
matrix
H
H
III
Inner mitochondrial
membrane
H
NAD
FAD
2 H
1
2 O2
H2O
H
ADP
P
ATP
H
Electron Transport Chain
Oxidative Phosphorylation
Chemiosmosis
6.12 Review: Each molecule of glucose yields many
molecules of ATP
• Recall that the energy payoff of cellular
respiration involves
1. glycolysis,
2. alteration of pyruvate,
3. the citric acid cycle, and
4. oxidative phosphorylation.
© 2012 Pearson Education, Inc.
6.12 Review: Each molecule of glucose yields many
molecules of ATP
• The total yield is about 32 ATP molecules per
glucose molecule.
• This is about 34% of the potential energy of a
glucose molecule.
• In addition, water and CO2 are produced.
© 2012 Pearson Education, Inc.
Figure 6.12
CYTOPLASM
Electron shuttles
across membrane
2 NADH
Mitochondrion
2 NADH
or
2 FADH2
6 NADH
2 NADH
Glycolysis
2
Pyruvate
Glucose
Pyruvate
Oxidation
2 Acetyl
CoA
Citric Acid
Cycle
2 FADH2
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
Maximum
per glucose:
2
ATP
by substrate-level
phosphorylation
2
ATP
by substrate-level
phosphorylation
 about
28 ATP
by oxidative
phosphorylation
About
32 ATP