TCA Cycle Facts

What happens during the TCA cycle?

Pyruvate from glycolysis is converted to acetyl-CoA and oxidized to CO2

How many ATP are produced from TCA cycle?

2 ATP

The pyruvate dehydrogenase complex is made up of how many enzymes?

3

What steps of the TCA cycle produce CO2?

Steps 3 + 4

What step of TCA cycle is irreversible?

Step 1 (Citrate Synthase)

What is citrate synthase rxn (step 1) inhibited by?

NADH + succinyl-CoA

What cofactor activates aconitase?

Fe2+

How does flouroacetate block the TCA cycle?

Trojan horse inhibitor— flouroacetate enters the TCA cycle, is converted to fluorocitrate (inhibitory) by citrate synthase, which then inhibits aconitase

What reaction has an intermediate?

Step 2 (Aconitase) Citrate > cis-Aconitate > Isocitrate

What reaction links the TCA cycle and the electron transport chain?

Isocitrate dehydrogenase step, produces NADH

What regulates Isocitrate dehydrogenase?

NADH + ATP (inhibitors) and ADP (activator; w/o it it is inactive)

What are two energy rich species produced by step 4?

Succinyl-CoA and NADH

Step 5 (Succinyl CoA) is an enzyme that performs

Substrate-level phosphorylation (provides energy for phosphorylation)

Enzymes of the TCA Cycle are (soluble or insoluble)?

Soluble (found in mitochondrial matrix)

Succinate dehydrogenase is

An integral membrane protein tightly associated with the inner mitochondrial membrane

Succinate dehydrogenase produces

2 FAD (not exergonic enough to reduce NAD+)

The last step of the TCA Cycle is highly (exergonic/endergonic)?

Endergonic (G = +30)

The primary sites of regulation in the TCA cycle are___. They are inhibited by NADH

1. Citrate synthase

2. Isocitrate dehydrogenase

3. Alpha-Ketoglutarate Dehydrogenase

4. Pyruvate Dehydrogenase (lower G value)

ATP is an inhibitor of

1. Pyruvate dehydrogenase

2. Isocitrate dehydrogenase

Succinyl CoA inhibits

1. Citrate synthase

2. Alpha-Ketoglutarate Dehydrogenase

Acetyl-CoA activates

Oxaloacetate production

High levels of acetyl-CoA or NADH inhibit

Pyruvate dehydrogenase complex

Pyruvate dehydrogenase regulation

AMP activates, GTP inhibits

Isocitrate Dehydrogenase

Activated by ADP and NAD+

Inhibited by ATP and NADH