metabolism- oxidation of pyruvate and tricarboxylic acid cycle

where does the oxidation of pyruvate and the tricarboxylic acid cycle occur

it happens in the mitochondria matrix as this is where the enzymes needed are and the membrane involved for the electron transport system

what is the function of pyruvate dehydrogenase

it is the complex that contol the entry of pyruvate into the TCA cycle, it has 3 subunits:

• pyruvate dehydrogenase E1- decarboxylates pyruvate ( has a requirement of thiamine pyrophosphate )

• dihydrolioyl transfease E2- makes coA ( needs lipoamide )

• dihydrolipoyl dehydrogenase E3- converts reduced lipoamide into disulphide which is required for FAD

explain the steps involved in the formation of acetyl-coA

1. Thiamine pyrophosphate is added to pyruvate and CO₂ is released

2. lipoamide disulphide is added to acetyl group and a redox reaction occurs

3. disulphide exchange occurs to form acetyl coA and reduced lipoamide

4. reduced lipoamide is oxidised to disulphide using FAD

5. FADH₂ is oxidised by NADH which is fed into the electron transport system

what type of reactions fdoes the tricarboxylic acid cycle use

catabolic and anabolic reactions

what are the 4 stages of the tricarboxylic acid cycle

1. condensation and rearrangement

2. decarboxylation

3. formation of GTP

4. conversion to succinate to oxaloacetate

what are the net products of the tricarboxylic acid cycle

3NADH, H⁺ , 1FADH₂ ,1GTP

WHT CAN THE TRICARBOXYLIC ACID CYCLE ONLY WORK IN AEROBIC CONDITIONS

the oxygens role is to deoxidise the reduced cofactors ( NADh, FADh) by the electron transport system. this allow the cycle to continue

explain stage 1 of the TCA cycle- condensation and rearrangement

• citrate synthase catalyses a condensation of acetyl-coA and oxaloacetate

• hydrolysis of coA ester makes the reaction irreversible

• citrate undergoes a rearrangement to form isocitrate- this prepares for stage 2

explain stage 2 of the TCA cycle- decarboxylation

• isocitrate is converted into beta-ketoacid using NAD⁺

• beta-ketoacid loses a co₂

• 2-oxoglutarate is converted into succinyl-coa by a multi-enzyme complex

• this reaction is analogous to the reaction carried out by the pyruvate dehydrogenase ( TPP, lipoamide, coA-SH )

explain stage 3 of the TCA cycle- formation of GTP

• coA is displaced by inorganic phosphate to produce a mixed acid anhydride

• phosphate is transferred to an active site

• the transfer of the phosphate group onto the GDP forms GTP ( which can be used to form ATP )

explain what happens in the TCA cycle in stage 4- formation of oxaloacetate