Lecture 30: TCA Cycle Overview

Question 1

TCA Cycle

Answer 1

• nearly universal central catabolic pathway
• compounds from carbohydrates, fats, and proteins are oxidized to CO2
• most of the energy from oxidation is converted to reduced electron carriers NADH and FADH2

Question 2

Where do these reactions occur for the entry of acetyl-CoA?

Answer 2

eukaryotes-Mitochondrial Matrix

Bacteria-Cytosol

Question 3

What is the energy gain from one acetyl-CoA being oxidized?

Answer 3

3 NADH
1 FADH2
1 ATP (GTP)

Question 4

What is the result of the TCA cycle?

Answer 4

Release of 2 CO2

Question 5

Mitochondrion

Answer 5

Has two bilayer membranes:

• outer membrane
• inner membrane

Question 6

Outer membrane

Answer 6

• porous

- easy equilibration of material from the cytoplasm across this membrane to the intermembrane space

Question 7

Inner membrane

Answer 7

• 75% protein by weight
• completely closed
• transporters are needed for movement of molecules

Question 8

Where does the TCA cycle occur?

Answer 8

takes place inside the inner membrane of the mitochondrion

-reduced electron carriers accumulate in here (NADH and FADH2)

Question 9

What reactions are metabollically irreversible in TCA cycle

Answer 9

1, 3, and 4

Question 10

Pyruvate Dehydrogenase Reaction

Answer 10

entry of pyruvate into TCA cycle

-enzyme: Pyruvate Dehydrogenase Complex-> contains 3 types subunits

Question 11

E1 of the pyruvate dehydrogenase complex and what coenzyme is involved

Answer 11

pyruvate dehydrogenase

-TDP (aka TPP)

Question 12

E2 of the pyruvate dehydrogenase complex and what coenzyme is involved?

Answer 12

dihydrolipoamide acetyltransferase

-lipoyllysine

Question 13

E3 of the pyruvate dehydrogenase complex and what coenzyme is involved?

Answer 13

dihydrolipoamide dehydrogenase

-FAD

Question 14

What is the purpose of the coenzymes utilized in the pyruvate dehydrogenase complex?

Answer 14

take care of covalently attaching to pyruvate, transfer of H-CoA, and oxidation

Question 15

Rxn 1 of TCA cycle extra info

Answer 15

acetyl-CoA

• is a high energy compound
• used as a substrate which contributes to the Large standard free energy decrease
• making this reaction irreversible

Question 16

Rxn 2 of TCA cycle extra info

Answer 16

despite the +free energy value, the cell goes to the right because isocitrate is used immediately in the next reaction. so its concentration is kept very low

Question 17

Aconitase

Answer 17

contains

- iron sulfur coenzyme center and the Fe2+ of the iron-sulfur participates in binding and catalysis

Question 18

Succinate Dehydrogenase

Answer 18

-enzyme found in inner side of the inner mitochondrial membrane