Lecture 17 - TCA Cycle

Question 1

What are the 4 main steps of the TCA Cycle?

Answer 1

1. Glycolysis
2. Pyruvate Oxidation
3. Krebs Cycle
4. Electron transport

Question 2

TCA Cycle Characteristics

Answer 2

Takes place in mitochondria
Consists of eight main enzyme catalysed reactions
Aerobic

Question 3

Acetyl CoA

Answer 3

Comes from pyruvate (from glycolysis) and oxidation of fatty acids

Question 4

What happens between Glycolysis and the TCA Cycle

Answer 4

Pyruvate formed needs to be transported to mitochondria if aerobic
Pyruvate enters mitochondria through protein (pyruvate translocase) embedded in inner mitochondrial membrane
- pyruvate is - so enters mitochondria with simultaneous entry of H+

Question 5

Pyruvate Dehydrogenase Complex

Answer 5

Contains 5 enzymes
- E1, E2 and E3 channeling substrates
- 2 regulatory enzymes PDH kinase and PDH phosphatase
- Kinase turns it off when high NADH to NAD+ and ATP to ADP ratios
- Phosphatase turns on when reverse of above
Five coenzymes needed:
- TPP
- NAD+
- FAD
- Lipoic Acid
- CoA

Question 6

NADH Shuttles

Answer 6

Inner mitochondrial membrane impermeable to NADH
Therefore 2 shuttle mechanisms to transfer electrons from NADH
Glycerophosphate shuttle
- transfers electrons from cytoplasmic NADH to mitochondrial FAD
- produces 1.5 ATP for each cytoplasmic NADH
Malate-aspartate shuttle
- transfers electrons from cytoplasmic NADH to mitochondrial NAD+
- produces 2.5 ATP for each cytoplasmic NADH

Question 7

What is the total ATP production of the TCA Cycle

Answer 7

30-32