Chapter 17 - Citric Acid cycle

What is the starting reaction to enter the citric acid cycle? What type of step is it?

pyruvate to acetyl CoA and it is a committed step

What is the initial entry enzyme for the citric acid cycle called?

pyruvate dehydrogenase complex

Where does the citric acid cycle occur?

mitochondrial matrix

Why CoA?

CoA is a thioester and is a high energy compound, by using that and oxidative decarboxylation (energy releaser) some of the energy released is captured as a high energy molecule

What is the biochemical role of the citric acid cycle?

acetyl CoA (pyruvate) to CO2 with accompanying production of NADH, FADH2, & GTP

what happens in pyruvate dehydrogenase (E1)?

carbanion of TPP + pyruvate to hydroxyethyl-TPP

What happens in dihydrolipoyl transacetylase (E2)?

Hydroxyethyl-TPP + Lipoamide to carbanion of TPP and Acetyllipoamide

What happens in dihydrolipoyl dehydrogenase (E3)?

dihydrolipoamide + FAD to lipoamide + FADH2 to FAD + NADH + H+

What is the first step of the citric acid cycle?

oxaloacetate + acetyl CoA to citrate

What is the driving force of the first step of the citric acid cycle?

the breaking of the high energy thioester bond

What is the second step of the citric acid cycle?

citrate to cis-aconitate to isocitrate

Why is step two so important?

it converts a tertiary alcohol, which can't be oxidized, into a secondary alcohol, which can be oxidized

What is the third step of the citric acid cycle?

Isocitrate dehydrogenase turns isocitrate to oxalosuccinate using NAD+ then uses H+ to make a-Ketoglutarate.

What is the fourth step of the citric acid cycle?

The a-Ketoglutarate dehydrogenase complex uses NAD+ and CoA to make succinyl CoA.

What is the fifth step of the citric acid cycle?

Succinyl CoA sythetase uses Pi and GDP to form succinate, CoA, and GTP.

What is the sixth step of the citric acid cycle?

Succinate dehydrogenase produces fumarate using FAD.

What is the seventh step of the citric acid cycle?

Fumarase adds water to fumarate to create L-malate.

What is the eighth step of the citric acid cycle?

Malate dehydrogenase uses NAD+ to create oxaloacetate from malate.

What is the driving step of step 8 of the citric acid cycle?

the step 1 of the next round, which is very favorable

How does product inhibition regulate the pyruvate dehydrogenase complex?

acetyl CoA and NADH inhibit when present in excess

GTP inhibits
AMP activates

What are some ways to inhibit the citric acid cycle?

step 1: inhibition by ATP

Step 3: inhibited by ATP and NADH (high energy)

step 4: inhibited by ATP

step 6: inhibited by oxaloacetate