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A detailed explanation of the citric acid cycle, also known as the krebs cycle. It outlines the eight steps of this metabolic process, the reactants and products of each step, and the enzymes involved. The document also explains how the cycle contributes to atp synthesis by producing nadh and fadh2.
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C CH 3
O CO (^2) CoA
C C CH 2 C
O
O -
O
O O - Oxaloacetate (4C) Citrate (6C)
C C CH 2 C
O
O -
O O -
HO CH 2 C O
O -
C C CH C
O
O -
O O -
CH 2 C O
O - HO
H
Isocitrate (6C)
C CH 2 CH 2 C
O
O -
O C O O -
α‐Ketoglutarate (5C)
CoA
Succinyl CoA (4C)
Succinate (4C)
Furmate (4C)
Malate (4C)
The CH 3 end of the acetyl CoA loses a proton and becomes bonded to the second carbonyl carbon (C=O) of oxyloacetate. The coenzyme (CoA) is subsequently lost with the input of water.
Acetyl CoA Oxaloacetate
An isomerization reaction takes place. This involves the removal of a water molecule and then the insertion of a water molecule. The hydroxyl (OH) group changes position to a different carbon as a result. isocitrate
This is the first of 4 oxidation steps in the cycle. The carbon carrying the hydroxyl group (OH) is converted to a carbonyl group (C=O). CO2 is lost from the intermediate and alpha ketoglutarate is produced. NADH is produced.
Another oxidation step that results in another loss of CO2. This reaction is very complex and is similar to the reaction that converts pyruvate to acetly CoA. NADH is produced.
CoA is displaced when an inorganic phosphate replaces CoA. Then the phosphate is used to phosphorylate GDP to make GTP. Later the high energy phosphate on GTP can be used to phosphorylate ADP to make ATP.
citrate
Isocitrate
Succinyl‐CoA
GTP Succinate
C CH 3
O CoA
C C CH 2 C
O
O -
O
O O -
S‐Citryl‐CoA intermediate Citrate
C C CH 2 C
O
O-
O O -
HO CH 2 C O
CoA
C C CH C
O
O -
O O -
HO CH 2 C O
O - H
C C CH C
O
O -
O O -
CH 2 C O
O - HO
H
C C
O
O -
CH 2 C O
O - C C O O -
H
Cis‐aconitate intermediate
C C CH C
O
O -
O O -
CH 2 C O
O - HO
H
C CH 2 CH 2 C
O
O -
O C O NAD+ NADH O - Oxylosuccinate intermediate (^) α‐Ketoglutarate
C CH 2 CH 2 C
O
O -
O C O O - α‐Ketoglutarate
CoA
CoA Succinyl‐CoA
In this, the third oxidation reaction, two hydrogens are removed from succinate. FAD+ becomes reduced to FADH2.
Succinate Furmate
C C
O
O -
C C O O -
H H