13. Metabolism 2; TCA cycle

Question 1

How many reactions are there in total?

Answer 1

8

Question 2

Describe the steps of the TCA cycle

Answer 2

1. pyruvate enters the mitochondrial matrix and is oxidised to acetate
2. the acetate combines with CoA to form acetyl-CoA
3. The C2 from acetyl coA combines with C4 oxaloacetate to form a c6 citrate
4. citrate to Isocitrate
5. Isocitrate to a-ketoglutarate yielding NADH and CO2
6. a-ketoglutarate to succinyl co-A yielding NADH and CO2
7. Succinyl co-A to succinate yielding GTP
8. succinate to fumarate yielding FADH2
9. Fumarate reacts with water to form malate
10. malate is oxidised to oxaloacetate yielding NADH and oxaloacetate can now re-enter the cycle

Question 3

Name the reactants\enzymes involved in the cycle

(hint; a clown in Kilimanjaro sings songs for money only

Answer 3

- acetyl co-A 
(citrate synthase)
- citrate
(aconitase)
- isocitrate
(Isocitrate dehydrogenase)
- a-ketoglutarate
(a-ketoglutarate dehydrogenase)
- succinyl co-a
(succinyl thiokinase)
- succinate
(succinate dehydrogenase)
- fumarate
(fumarase)
- malate
(malate dehydrogenase)
- oxaloacetate

Question 4

What is the only enzyme not located in the mitochondrial matrix? and where is it located?

Answer 4

succinylcholine dehydrogenase located in the inner mitochondrial membrane

Question 5

Control of the TCA cycle

Answer 5

• high ATP, NADH and acetyl co-A means plenty of energy
• high ADP and NAD+ means lack of energy
• high succinyl co-A and acetyl co-A means plenty of precursor molecules for biosynthetic pathways

Question 6

What are the products of the TCA cycle

Answer 6

• 3 NADH + H+
• FADH2
• GTP
• GTP + ADP to GDP + ATP
• 2 CO2