the krebs cycle

what is the Krebs Cycle?

it is a series of chemical reactions that reduced NAD by oxidation of 2-carbon acetyl groups. the reactions are controlled by enzymes & the Krebs Cycle occurs in the matrix of a mitochondrion.

what’s the “1st step” in the Krebs Cycle?

the binding of the acetate from the acetyl CoA wit a 4-carbon compound called oxaloacetate.

this releases the CoA from the acetyl CoA (the CoA will return to the link cycle)

now, the acetate & oxaloacetate will combine to form a 6-carbon compound called citrate or citric acid.

what’s the “2nd” step?

oxidative decarboxylation is involved - a CO2 molecule is removed & NAD is reduced to NADH + H+ (the H+ is sent to the Electron Transport Chain)

the 6-carbon citrate is now a 5-carbon compound

what’s the “3rd step”?

oxidative decarboxylation occurs again, and a CO2 is removed & NAD is reduced to NADH + H+ (H+ is again sent to Electron Transport Chain).

5-carbon compound is now a 4-carbon compound

what’s the “4th step?”

oxidative phosphorylation occurs - ADP changes to ATP

all 6 of the carbons from original glucose molecule are now released as 6 molecules of CO2.

in order to continue the cycle, oxaloacetate has to be regenerated

  • 4-carbon compound is oxidised/dehydrogenated

    • NAD is reduced to NADH

    • FAD is reduced to FADH

now the oxaloacetate can bind with another acetate, continuing the cycle


what’s the net yield from the Krebs Cycle, per glucose molecule?

2 ATP (since glucose divides into 2 pyruvates, and one pyruvate will go through the cycle and produce one ATP, 2 ATP are produced per glucose), 6 NADH + H2 , 2FADH2

how many times does the Krebs Cycle have to turn per glucose molecule?

2 times (it turns one time for each pyruvate)