2.2 Cell Metabolism 2

Question 1

what does the TCA cycle produce?

Answer 1

Each turn produces:

• 2 CO2 (waste)
• 3 NADH
• 1 GTP
• 1 FADH2

Question 2

Where does the TCA cycle operate and under what conditions?

Answer 2

Aerobic conditions and in the mitochondrial matrix

Question 3

How do amino acids enter the TCA cycle?

Answer 3

Amine group removed and excreted as urea
Carbon skeleton funnelled into production of glucose or fed into kerbs cycles

Degradation of all 20 amino acids gives rise to only 7 molecules: pyruvate, acetyl CoA, acetoacetyl CoA, a-ketoglutarate, succinyl CoA, fumarate and oxaloacetate

Question 4

What are glucogenic amino acids?

Answer 4

For glucose via gluconeogenisis

Question 5

What are ketogenic amino acids?

Answer 5

Amino acids which give rise to ketone bodies
Predominantly hydrophobic

Question 6

What is a transamination reaction?

Answer 6

Group transfer reaction
When amine group from one amino acid is transferred a keto acid forming a new pair of amino and keto acids.

Question 7

How is NADH transported into the mitochondria from the cytosol?

Answer 7

• glycerol phosphate shuttle
• malate aspartate shuttle

Question 8

2 steps of glycerol phosphate shuttle

Answer 8

1) Cytosolic glycerol 3-phosphate dehydrogenase transfers electrons from NADH to DHAP to generate glycerol 3-phosphate

2) A membrane bound mitochondrial form of the same enzyme transfers the electrons to FAD which get passed to co-enzyme Q (part of the electron transport chain)

Question 9

What happens in the malate aspartate shuttle?

Answer 9

1) Oxaloacetate in cytoplasm is reduced to malate (and NADH oxidised to NAD+) by MDH (malate dehydrogenase) in a redox reaction

2) Malate shuttled into mitochondria where mitochondrial MDH does reverse reaction and electrons are recaptured onto NAD+ to form NADH and oxaloacetate formed

3) The keto acid oxaloacetate and amino acid glutamate undergo a transamination reaction by AT (aspartate transaminase) to form the keto acid alpha-ketoglutarate and amino acid aspartate

4) Aspartate shuttled out of mitochondrion and reverse transamination reaction happens by cytosolic AT, bringing us back to the first oxaloacetate

Question 10

What kind of transporters are used to shuttle the molecules between the cytosol and mitochondrion?

Answer 10

They are antiporters since they transport in 2 directions
(As malate enters the mitochondrion, the alpha-ketoglutarate made in the mitochondrial transamination reaction leaves it

As aspartate leaves the mitochondrion, the glutamate produced in the cytosolic redox reaction enters it)

Question 11

How many ATP does the oxidation of 1 acetyl CoA give?

Answer 11

3 x NADH (3 ATP)

1 x FADH2 (2 ATP)

1 x GTP (ATP alternative)

= 12 ATP