Short Answer Questions - Metabolism of Amino Acids and Porphyrins
1. Name the enzyme which regulates the urea cycle.
Carbamoyl phosphate synthetase.
2. Which metabolic disorder is associated with orotic aciduria, hyperammonaemia and low blood urea (blood urea nitrogen)?
Ornithine transcarbamoylase (OTC) deficiency.
3. The essential amino acids must be included in the human diet: name them.
Phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, leucine and lysine.
4. Name all the amino acids which can be metabolised to glucose during periods of fasting/starvation.
The following are totally metabolised to glucose: glycine, serine, cysteine, alanine, aspartate, histidine, glutamate, proline, arginine, methionine, threonine and valine. Also, the following are partially metabolised to glucose: phenylalanine, tyrosine, isoleucine and tryptophan.
5. Name all the amino acids which can be metabolised to form ketone bodies during periods of fasting/starvation.
Lysine and leucine are totally metabolised to the ketone bodies. The following are partially metabolised to ketone bodies: phenylalanine, tyrosine, isoleucine and tryptophan.
6. Describe the enzymic disorders which cause homocystinuria.
Classical homocystinuria is caused by cystathionine ß-synthase deficiency. Methionine synthase deficiency (primary or due to inadequate dietary folic acid and/or vitamin B12) also causes homocystinuria
7. Describe the enzymic disorders which cause phenylketonuria.
Classic phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase (PAH). PKU can also be caused by deficiency of tetrahydrobiopterin, a cofactor for PAH activity.
8. Describe the neurohormone deficiency in Parkinson’s disease.
Deficiency of dopamine in the substantia nigra region of the brain.
9. Describe the hormonal abnormalities in phaeochromocytoma.
Phaeochromocytoma results in excessive production of adrenaline (epinephrine) and/or noradrenaline (norepinephrine).
10. Tryptophan is used for the biosynthesis of which vitamin?
Niacin.
11. Tryptophan can be metabolised by both the kynurenine pathway and the indoleamine pathway. According to the monoamine hypothesis, which clinical disorder is associated with inappropriately low activity of the indoleamine pathway?
Depression.
12. Increased urinary δ-aminolevulinic acid (δ-ALA) is associated with poisoning by which metal?
Lead.
13. Which metabolite is present in urine in increased amounts in ‘acute intermittent porphyria’?
Porphobilinogen (PBG).
14. What is Gilbert’s syndrome?
A benign, chronic, low-grade, hyperbilirubinaemia caused by a mild deficiency of UDP-glucuronyl transferase. It is asymptomatic and very common, occurring in approximately 5% of the population.
