Download Lecture 019--Respiration 3 (Kreb`s Cycle)

Chapter 9.2
Cellular Respiration:
Pyruvate Oxidation &
Citric Acid Cycle
OVERVIEW OF GLYCOLYSIS
1
2
3
6-carbon glucose
(Starting material)
2 ATP
P
P
6-carbon sugar diphosphate
P
P
6-carbon sugar diphosphate
P
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
NADH
2 ATP
reactions. Glycolysis begins with the
addition of energy. Two high-energy
phosphates from two molecules of
ATP are added to the six-carbon
molecule glucose, producing a sixcarbon molecule with two
phosphates.
NADH
2 ATP
3-carbon
pyruvate
Priming reactions. Priming
P
3-carbon
pyruvate
Cleavage reactions. Then, the
Energy-harvesting reactions.
six-carbon molecule with two
phosphates is split in two, forming
two three-carbon sugar
phosphates.
Finally, in a series of reactions,
each of the two three-carbon sugar
phosphates is converted to
pyruvate. In the process, an
energy-rich hydrogen is harvested
as NADH, and two ATP molecules
are formed.
Glycolysis is only the start
 Glycolysis
glucose      pyruvate
6C
2x 3C
 but pyruvate has more energy to yield!
3 more C to strip off (to oxidize)
 if O2 is not available, pyruvate is reduced to
regenerate NAD+ (meaning that NADH is
oxidized to NAD+)

Glycolysis is only the start
 Glycolysis
glucose      pyruvate
6C
2x 3C
 but pyruvate has more energy to yield!
3 more C to strip off (to oxidize)
 if O2 is available, pyruvate enters
mitochondria
 enzymes of Krebs cycle complete oxidation
of sugar to CO2

pyruvate       CO2
3C
1C
Cellular Respiration
Oxidation of Pyruvate
 Pyruvate enters mitochondria
2x
[
pyruvate    acetyl CoA + CO2
3C
2C
NAD

Waiting to
exhale?
1C
]
NADH
3 step oxidation process (on next slide)
 releases 1 CO2 (count the carbons!)
 reduces NAD  NADH (stores energy—endergonic)
 2C combines with CoA, producing acetyl CoA
 Acetyl CoA enters Krebs cycle

where does CO2 go?
Pyruvate oxidized to Acetyl CoA
reduction
x2
oxidation
Yield = 2C compound + CO2 + NADH x2
Krebs cycle
 a.k.a. 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 AFTER 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
respiration)
Count the carbons!
pyruvate
3C
2C
acetyl CoA
6C
4C
citrate
x2
4C
This happens
twice for each
glucose
molecule!
6C
oxidation
of sugars
CO2
5C
4C
4C
4C
CO2
Count the electron carriers!
pyruvate
3C
2C
acetyl CoA
6C
4C
NADH
x2
4C
4C
citrate
6C
reduction
of electron
carriers
ADP
FADH2
4C
ATP
This happens
twice for each
glucose
molecule!
4C
CO2
NADH
5C
CO2
NADH
So we fully
oxidized
glucose
C6H12O6

CO2
& ended up
with a net gain
of 4 ATP!
What
Is 4 ATP
was
all
thewe
point?
get?
NADH & FADH2
 Krebs cycle
produces large
quantities of
electron carriers
NADH
 FADH2

 stored energy!
 they go to ETC
What’s so
important
about NADH
and FADH2?
Energy stored from Pyruvate Oxidation
and Krebs Cycle
4 NAD + 1 FAD
2x
4 NADH + 1 FADH2
pyruvate          CO2
3C
3x 1C
1 ADP
Stored
energy?
What good
is that?
1 ATP
Net gain = 2 ATP
= 8 NADH
= 2 FADH2
So why the Krebs cycle?
 If the yield is only 2 ATP, then why?

value of NADH & FADH2
 electron carriers
 reduced molecules store energy!
 to be used in the Electron Transport Chain
Ohhhh! I see. We
just are slowly
releasing the
chemical energy
from the bonds of
glucose! Not so
bad, right?
RIGHT?!?
Cellular Respiration
What’s the point?
ATP
The Point is to Make ATP!
Any Questions??