Endogenous Catecholamines

Question 1

Regarding tyrosine:

A. Tyrosine is an essential amino acid

Answer 1

False. As well as dietary sources, it is also synthesized in the liver from phenylalanine.

Question 2

Regarding tyrosine:

B. In phenylketonuria, there is a congenital absence of phenylalanine hydroxylase

Answer 2

True. This leads to accumulation of phenylalanine.

Question 3

Regarding tyrosine:

It is found in the adrenal medulla

Answer 3

True. Tyrosine is manufactured by the chromaffin cells in the adrenal medulla.

Question 4

Regarding tyrosine:

It is metabolised to L-Dopa by tyrosine kinase

Answer 4

False. It is metabolised to L-Dopa by tyrosine hydroxylase; this is the rate-limiting step of the synthetic pathway.

Question 5

Regarding tyrosine:

L-Dopa differs from tyrosine by the addition of a single hydroxyl group

Answer 5

True

Question 6

Regarding endogenous catecholamines:

The adrenal medulla releases 80% noradrenaline and 20% adrenaline

Answer 6

False. The adrenal medulla releases 80% adrenaline and 20% noradrenaline.

Question 7

Regarding endogenous catecholamines:

The half-life of adrenaline is 10 minutes

Answer 7

False. It is only 1-3 minutes.

Question 8

Regarding endogenous catecholamines:

Phenylethanolamine-N-methyltransferase (PNMT) catalyzes conversion of noradrenaline to adrenaline

Answer 8

True

Question 9

Regarding endogenous catecholamines:

The clinical difference between noradrenaline and adrenaline arises from their different affinity for the β1 adrenoceptor

Answer 9

False. Adrenaline and noradrenaline differ mainly in their effects at β2 adrenoceptors, to which noradrenaline has a much lower affinity.

Question 10

Regarding endogenous catecholamines:

Beta receptors are G protein-coupled

Answer 10

True. Alpha receptors are also G protein-coupled.