citric acid cycle

formation of citrate

step 1

carried out by citrate synthase

acetate from acetyl-CoA is combined with oxaloacetate

isomerization of citrate to isocitrate

step 2

reaction carried out by enzyme aconitase

requires Fe²⁺

OH moved to C-3 of isocitrate

a-ketoglutarate formation

step 3

reaction carried out by the enzyme isocitrate dehydrogenase

NAD⁺ reduced to NADH

second loss of CO₂

succinyl-CoA formation

step 4

carried out by a-ketoglutarate dehydrogenase

a-ketoglutarate oxidation to reduce NAD⁺ to NADH

5 carbon a-ketoglutarate to 4 carbon succinyl

THIRD CO₂ LOSS

succinate formation

step 5

carried out by succinyl-CoA synthetase

P_i and energy from succinyl-CoA breakage is used to form GTP

P_i is transferred to ADP by nucleosidediphosphate kinase

only ATP made in TCA cycle

fumarate formation

step 6

reaction carried out by enzyme succinate dehydrogenase

enzymes is an integral mitochondrial inner membrane protein

FAD acts as an e- acceptor instead of NAD+

bond between C 2&3 is oxidized to double bond

malate formation

step 7

reaction carried out by fumarase

double-bond of fumarate is hydrogenated by H2O

oxaloacetate regeneration

step 8

carried out by malate dehydrogenase

pathway regenerated

can now react with another acetyl-coa