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Krebs cycle simplified, how it occurs and diagrams
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Objectives
1.
History and introduction of citric acid cycle
2.
Conversion of pyruvate to activated acetate by pyruvate dehydrogenase
3.
Explain Reactions of citric acid cycle
4.
Amphibolic nature of Citric acid cycle
OVERVIEW
Citric acid cycle is also called
Tricarboxylic acid (TCA) cycle
or
Krebs cycle
is a sequence
of
biochemical reactions that occurs in all aerobic organisms for energy generation. Energy is
generation is carried out by the oxidation of acetate, which is derived from
carbohydrates,
lipids and proteins converted into Co
2
and chemical energy stored in the
form of adenosine triphosphate (ATP). Furthermore, the TCA cycle supplies precursors
1
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for synthesis of several amino acids and reducing agent such as NADH, which involves in
various
other biochemical reactions. TCA cycle is one of the initially established mechanism of
cellular metabolism suggested by the central importance in various biochemical pathways.
The name of this biochemical pathway is derived from tricarboxylic acid (e.g. citric acid) .
Citric
acid is first utilized and then regenerated by these sequential reactions to complete the cycle.
The major function of these two closely associated pathways is the oxidative breakdown of
nutrients into production of usable energy in the form of ATP.
In eukaryotic cells, the Krebs cycle occurs in the mitochondrial matrix. In prokaryotic cells
the TCA reaction occurs in the cytosol through the proton gradient for energy generation.
In 1935 Albert Szent-Gyorgyi showed that
Succinate
Fumarate Malate Oxaloacetate
Carl Martius and Franz Knoop showed
Citrate
cis-aconitate
Isocitrate
α ketoglutarate
Succinate
Fumarate
Malate
Oxaloacetate
- Overall reaction of the citric acid cycle is:
3NAD
+
+ FAD + GDP + P
i
+ acetyl-CoA 3NADH + FADH
2
+ GTP + CoA + 2CO
2
from glucose:
Glucose + 2NAD
+
+ 2ADP + 2P
i
→ 2pyruvate + 2NADH + 2ATP
2
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