Carbohydrate metabolism

Question 1

PFK is activated by a high ……. : ……. ratio

Answer 1

High insulin:glucagon

Question 2

Muscle PFK is allosterically inhibited by a high ATP:AMP ratio. True or false?

Answer 2

True

Question 3

By what method is pyruvate kinase regulated?

Answer 3

By phosphorylation/dephosphorylation depending on insulin:glucagon ratio

Question 4

In which tissues does anaerobic respiration occur?

Answer 4

RBC’s and skeletal muscle

Question 5

In galactosaemia, which enzymes may be deficient?

Answer 5

Galactokinase and UDP uridyl-transferase

Question 6

When galactose accumulates in galactosaemia, what pathways can it enter?

Answer 6

It is converted to galacitriol via the enzyme aldose reductase. This pathways depletes NADPH.

Question 7

How do you treat galactosaemia?

Answer 7

No lactose in the diet

Question 8

What is the enzyme involved in the pentose phosphate pathway?

Answer 8

Glucose 6 phosphate dehydrogenase

Question 9

What are common symptoms of a G-6-P DH deficiency? (2)

Answer 9

Anaemia and cataracts

Question 10

Which tissues is the pentose phosphate pathway important in?

Answer 10

RBCs, adipose tissue and the liver

Question 11

What is essential fructosaria?

Answer 11

It is the lack of fructokinase

Question 12

If the aldolase is deficient resulting in fructose intolerance. Why is the condition harmful?

Answer 12

Accumulation of fructose 1-phosphate is toxic

Question 13

What is the main clinical sign of essential fructosaria?

Answer 13

Fructose in the urine

Question 14

What is the enzyme that catalyses the link reaction?

Answer 14

Pyruvate dehydrogenase

Question 15

How is pyruvate dehydrogenase regulated?

Answer 15

By dephosphorylation/phosphorylation

Question 16

What is the equation for the link reaction?

Answer 16

Pyruvate + CoA + NAD+ –> Acetyl-CoA + CO2 + H^+ + NADH

Question 17

Pyruvate dehydrogenase when phosphorylated is inhibited. What are the name of 4 substrates that inhibit PDH?

Answer 17

Acetyl-CoA, NADH, ATP and citrate

Question 18

Give an example of a substrate that activates PDH via dephosphorylation. (5)

Answer 18

Pyruvate, CoASH, NAD+, ADP, Insulin

Question 19

Give the two key enzymes involved in the Krebs cycle?

Answer 19

Isocitrate dehydrogenase and a-ketoglutarate dehydrogenase

Question 20

Where does the Kreb’s cycle occur?

Answer 20

The mitochondrial matrix

Question 21

What effect does cyanide have on oxidative phosphorylation?

Answer 21

It inhibits the proton translocating complex

Question 22

What is thermogenin and where is it found?

Answer 22

It is a natural uncoupler and found in brown adipose tissue

Question 23

What is the difference between the enzymes involved in oxidative phosphorylation and substrate level phosphorylation?

Answer 23

The enzymes in oxidative are membrane bound as opposed to soluble enzymes

Question 24

In which process does energy coupling take place directly? Oxidative or substrate level?

Answer 24

Substrate level phosphorylation

Question 25

What allosterically inhibits hexokinase?

Answer 25

G-6-P is an allosteric inhibitor

Question 26

What are the four enzymes involved in gluconeogenesis?

Answer 26

Pyruvate carboxykinase, PEPCK, Fructose 1,6 bisphophotase and glucose 6 phosphotase