Krebs Cycle

Front 1

Reaction 1

Back 1

Condensation-citrate is formed from acetyl CoA and oxaloacetate. Irreversible, committing the 2 C acetyl group to the Krebs cycle. Inhibited when too much ATP and stimulated when twoo low ATP.

Front 2

Reaction 2 and 3

Back 2

Isomerization - Hydroxyl group of citrate must be repositioned. First, a water molecule is removed from one carbon, then water is added to a different carbon. the H group an dan OH. An H group and OH group change positions. This makes isocitrate.

Front 3

Reaction 4

Back 3

The first oxidation - isocitrate is oxidized, yielding a pari of electrons that reduce a molecule of NAD to NaDH. Then the oxidized intermediate is decarboylated, the central carboxyl group splits off to form CO2, yielding a 5 carbon molecule called a-ketoglutarate

Front 4

Reaction 5

Back 4

The second oxidatoin - a-keto. is decarboxylated by a multicenzyeme complex similar to pyruvate dehydrogenase. The succinyl group left after removal of CO2 joins to coenzyme A, forming succinyl CoA. two electrons are extracted, reducing nad-nadh

Front 5

reaction 6

Back 5

substrate - level phosphorylation - linkage between the 4C succinyl group and coA is a high energy bond. bond is celeaved and energy released drives the phosiphorylation of guanosine diphospahte, transferring ADP-ATP

Front 6

reaction 7

Back 6

the third oxidation - succinate is oxidized to fumarate by an enzyme located in the inner mitochondrial membrane.

Front 7

reaction 8 and 9

Back 7

regeneration of oxaloacetate - water is added to fumarate to form malate. Malate is oxidized, yielding a 4 C molecule of oxaloacetate and 2 electrons reduce nad to nadh. Oxaloacetate is now free to combine with another 2 carbon acetyl group form acetyl coA and reinintiate tthe cycle.