Biochemistry Part 6

Question 1

How is redox balance maintained?

Answer 1

Only limited amounts of NAD are present in a cell

Glycolysis reduced NAD+ to NADH and +

NADH must be re-oxidised to let glycolysis continue

NAD+ is regenerated through the oxidative metabolism of pyruvate

Question 2

What are the three stages of oxidation of pyruvate?

Answer 2

1. Acetyl-CoA production
   (Citric acid cycle)
2. Acetyl-CoA oxidation
   (Krebs cycle)
3. Electron transfer and oxidative phosphorylation
   (TCA cycle)

Question 3

What is the roll of NADH?

Answer 3

Delivers electrons to the respiratory chain

Question 4

Where does the TCA cycle occur?

Answer 4

In the mitochondrial matrix

Question 5

How does pyruvate enter the mitochondrial matrix?

Answer 5

H+ gradient from cytosol to matrix

Pyruvate transporterL H+/pyruvate symport by facilitated diffusion

Question 6

How is pyruvate metabolised to Acetyl-CoA in the matrix?

Answer 6

Pyruvate dehydrogenase complex catalyses decarboxylation of pyruvate to acetyl-CoA

Question 7

What does PDC consist of?

Answer 7

3 enzymes

Question 8

How is PDC regulated?

Answer 8

allosterically regulated by phosphorylation

Question 9

What does PDC determine?

Answer 9

Glucose oxidation in well oxygenated tissues

Question 10

Is the metabolism of pyruvate reversible?

Answer 10

No

Question 11

What are the three enzymes involved in PDC?

Answer 11

Pyruvate dehydrogenase

Dihydrolipoyl transacetylase

Dihydrolipoyl Dehydrogenase

Question 12

What are the four reactions of PDC?

Answer 12

1. Pyruvate loses CO2 and HETPP is formed
2. Hydroxyethyl group is transferred to lipoic acid and oxidised to form acetyl dihydrolipoamide
3. Acetyl group is transferred to CoA
4. Dihydrlipoamide is deoxidised

Question 13

How many reactions are involved in the TCA cycle?

Answer 13

Eight

Question 14

What happens to the two-carbon unit from acetyl-coa?

Answer 14

Condenses with a four-carbon unit; resulting six-carbon unit is decarboxylates twice (yields CO2)

Question 15

How many oxidation reactions are involved in the tea cycle?

Answer 15

Four

• yield NADH + H+ and FADH2
• one GTP is formed

Question 16

Where are all enzymes of the TCA cycle located?

Answer 16

In the mitochondrial matrix apart from succinate dehydrogenase

Question 17

Where is succinate dehydrogenase located?

Answer 17

Inner mitochondrial membrane

Question 18

What do all products of stage II metabolism give rise to?

Answer 18

Acetyl-CoA and as a result can be oxidised completely to CO2 via the CO2 cycle

Question 19

What does each turn of the TCA cycle involve?

Answer 19

• uptake of two carbon atoms as acetyl-CoA and the release of two carbon atoms as CO2
• Transfer three pairs of electrons to NAD+ to form NADH + H+ and one pair of electrons to reduce FAD to FADH2
• One substrate level phosphorylation reaction results in the formation of GTP from GDP and Pi

Question 20

What does high ATP, NADH and acetyl-CoA means…

Answer 20

Plenty of energy

Question 21

What does high ADP and NAD+ means…

Answer 21

Lack of energy

Question 22

What does high succinyl-CoA and acetyl-CoA and acetyl-CoA mean?

Answer 22

Plenty of precursor molecules for biosynthetic reactions

Question 23

What is PDC deficiency?

Answer 23

Stage II metabolic disorder

-gene located on C chromosome

Question 24

How does PDC deficiency present?

Answer 24

Largely as neurological disease in children

• respiratory problems
• persistent lactic acidosis
• retardation and seizures
• poor muscle tone (hypotonia) and lack of coordination

Question 25

What is HLRCC?

Answer 25

Hereditary leiomymatosis and renal cell cancer

-defect in fumarate hydrates

Question 26

How does HLRCC present?

Answer 26

Multiple systemic benign and malignant tumours

• kidney particular ice of malignant metastasis
• link between TCA cycle and cell proliferation