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

Colonie High AP Biology
DeMarco/Goldberg
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
P
6-carbon sugar diphosphate
P
6-carbon sugar diphosphate
P
P
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
P
3-carbon sugar 3-carbon sugar
phosphate
phosphate
NADH
NADH
2 ATP
2 ATP
3-carbon
pyruvate
Priming reactions. Priming
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.
Glycolysis is only the start
 Glycolysis
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
glucose      pyruvate
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+)

Cleavage reactions. Then, the
Glycolysis is only the start
glucose      pyruvate
6C
3-carbon
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
Cellular Respiration
1C
Oxidation of Pyruvate
 Pyruvate enters mitochondria
2x
[
pyruvate    acetyl CoA + CO2
3C
2C
NAD

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?
Colonie High AP Biology
DeMarco/Goldberg
Pyruvate oxidized to Acetyl CoA
Krebs cycle
 a.k.a. Citric Acid Cycle
reduction


in mitochondrial matrix
8 step pathway
Hans Krebs
1900-1981
 each catalyzed by specific enzyme
 step-wise catabolism of 6C citrate molecule
 Evolved AFTER glycolysis

does that make evolutionary sense?
 bacteria  3.5 billion years ago (glycolysis)
x2
oxidation
 free O2  2.7 billion years ago (photosynthesis)
 eukaryotes  1.5 billion years ago (aerobic
respiration)
Yield = 2C compound + CO2 + NADH x2
Count the carbons!
pyruvate
3C
2C
Count the electron carriers!
acetyl CoA
6C
4C
citrate
x2
4C
This happens
twice for each
glucose
molecule!
pyruvate
4C
CO2
4C
CO2
6C
C6H12O6

CO2
& ended up
with a net gain
of 4 ATP!
ADP
FADH2
4C
NADH & FADH2
 Krebs cycle
produces large
quantities of
electron carriers


citrate
NADH
FADH2
 stored energy!
 they go to ETC
This happens
twice for each
glucose
molecule!
6C
reduction
of electron
carriers
ATP
So we fully
oxidized
glucose
acetyl CoA
x2
4C
5C
4C
2C
4C
NADH
6C
oxidation
of sugars
4C
3C
4C
CO2
NADH
5C
CO2
NADH
Colonie High AP Biology
DeMarco/Goldberg
Energy stored from Pyruvate Oxidation
and Krebs Cycle
[
2x
4 NAD + 1 FAD
pyruvate          CO2
3C
3x 1C
1 ADP
]
4 NADH + 1 FADH2
1 ATP
Net gain = 2 ATP
= 8 NADH
= 2 FADH2
Cellular Respiration
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