Transcript Cellular Respiration Oxidation of Pyruvate Krebs Cycle

Cellular Respiration
Stage 2 & 3:
Oxidation of Pyruvate
Krebs Cycle
AP Biology
2006-2007
Glycolysis is only the start
 Glycolysis
glucose      pyruvate
6C
2x 3C
 Pyruvate has more energy to yield


if O2 is available, pyruvate enters mitochondria
enzymes of Krebs cycle complete the full
oxidation of sugar to CO2
pyruvate       CO2
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3C
1C
Cellular respiration
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Mitochondria — Structure
 Double membrane energy harvesting
organelle


smooth outer membrane
highly folded inner membrane
 CALLED - Cristae- site of ETC

intermembrane space

Matrix- site of Kreb Cycle
 inner fluid-filled space


DNA, ribosomes
enzymes
What cells would have
AP
Biology
a lot
of mitochondria?
outer
intermembrane
membrane
inner
space
membrane
cristae
matrix
mitochondrial
DNA
Mitochondria – Function
Oooooh!
Form fits
function!
Dividing mitochondria
Membrane-bound proteins
Who else divides like that? Enzymes
bacteria!
What does this tell us about
the evolution of eukaryotes?
Endosymbiosis!
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Advantage of highly folded inner
membrane?
More surface area for membranebound enzymes
Oxidation of pyruvate- (Transition reaction)
 Pyruvate enters mitochondrial matrix
[
2x pyruvate    acetyl CoA + CO2
3C
2C
1C
NAD
Where
does the
CO2 go?
Exhale!
3 step oxidation process
 releases 2 CO2 (count the carbons!)
 reduces 2 NAD  2 NADH (moves e )
 produces 2 acetyl CoA


Acetyl CoA enters Krebs cycle
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]
Pyruvate oxidized to Acetyl CoA
reduction
NAD+
Pyruvate
C-C-C
[
Coenzyme A
CO2
Acetyl CoA
C-C
oxidation
(Acetyl CoA)
2 x Yield = 2C sugar + NADH + CO2
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]
Krebs cycle
1937 | 1953
 aka Citric Acid Cycle
in mitochondrial matrix
 8 step pathway

 each catalyzed by specific enzyme
Hans Krebs
1900-1981
 step-wise catabolism of 6C citrate molecule
 Evolved later than glycolysis

does that make evolutionary sense?
 bacteria 3.5 billion years ago (glycolysis)
 free O2 2.7 billion years ago (photosynthesis)
 eukaryotes 1.5 billion years ago (aerobic
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respiration = organelles  mitochondria)
The Kreb Cycle
• Occurs in the matrix of the
•
mitochondria
Is also called the Citric Acid
Cycle
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Count the carbons!
pyruvate
3C
2C
6C
4C
This happens
twice for each
glucose
molecule
4C
citrate
oxidation
of sugars
4C
6C
CO2
x2
4C
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acetyl CoA
5C
4C
CO2
Count the electron carriers!
pyruvate
3C
6C
4C
NADH
This happens
twice for each
glucose
molecule
2C
4C
4C
citrate
reduction
of electron
carriers
x2
FADH2
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acetyl CoA
4C ATP
CO2
NADH
6C
CO2
NADH
5C
4C
CO2
NADH
So we fully
oxidized
glucose
C6H12O6

CO2
& ended up
with 4 ATP!
What’s the
point?
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AP Biology
Electron Carriers = Hydrogen Carriers
H+
 Krebs cycle
produces large
quantities of
electron carriers
NADH
 FADH2
 go to Electron
Transport Chain!

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What’s so
important about
electron carriers?
H+
H+
H+
+
H+ H H+
H+
ADP
+ Pi
ATP
H+
Energy accounting of Krebs cycle
4 NAD + 1 FAD
4 NADH + 1 FADH2
2x pyruvate          CO2
3C
3x 1C
1 ADP
1 ATP
ATP
Net gain = 2 ATP (Substrate-level-phosphorylation)
= 8 NADH + 2 FADH2
AP Biology
Value of Krebs cycle?
 If the yield is only 2 ATP then how was
the Krebs cycle an adaptation?

value of NADH & FADH2
 electron carriers & H carriers
 to be used in the Electron Transport Chain
like $$
in the
bank
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http://highered.mcgrawhill.com/sites/0072507470/student_vie
w0/chapter25/animation__how_the_kr
ebs_cycle_works__quiz_1_.html
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What’s the
point?
The point
is to make
ATP!
ATP
AP Biology
2006-2007
H+
And how do we do that?
H+
H+
H+
H+
H+
H+
H+
 ATP synthase
set up a H+ gradient
 allow H+ to flow
through ATP synthase
 powers bonding
of Pi to ADP

ADP + P
ADP + Pi  ATP
ATP
H+
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But…
Have we done that yet?
NO!
The final chapter
to my story is
next!
Any Questions?
AP Biology
2006-2007