Chapter 18 Self-test questions

. Which of the following statements about the metabolism of amino acids is correct?

Essential amino acids can be formed from other amino acids supplied in the diet.

Excess dietary amino acids cannot be converted to other metabolites.

Excess dietary amino acids that cannot be oxidised are stored as muscle proteins.

Essential amino acids cannot be formed from other amino acids but must be supplied in the diet.

. Which of the following statements about the role of glutamate dehydrogenase is correct?

Glutamate dehydrogenase has an FAD prosthetic group.

Glutamate dehydrogenase has a pyridoxal phosphate cofactor.

Glutamate dehydrogenase transaminates glutamate producing α-ketoglutarate.

Glutamate dehydrogenase oxidatively deaminates glutamate producing α-ketoglutarate.

. Which of the following statements about transamination reactions is correct?

Transamination reactions involve ATP hydrolysis.

Transamination reactions are irreversible.

Transamination reactions require NAD⁺ or NADP⁺.

Transamination reactions require pyridoxal-5'-phophate.

. Which of the following statements about the urea cycle is correct?

Argininosuccinate is lysed to urea and ornithine in the urea cycle.

Carbamoyl phosphate supplies both of the nitrogen atoms of urea in the urea cycle.

The formation of urea from the urea cycle yields energy.

Arginine is hydrolysed to urea and ornithine in the urea cycle.

. Which of the following statements about aminolevulinate synthase (ALA synthase) is correct?

ALA synthase synthesis decreases in individuals treated with drugs such as barbiturates.

ALA synthase catalyses the rate-limiting reaction in haem degradation.

ALA synthase catalyses the rate-limiting reaction in haem synthesis.

ALA synthase is decreased in patients with acute intermittent porphyria.

. Which of the following statements about amino acid and protein metabolism is true?

Most amino acids are both ketogenic and glucogenic.

Both sulphur containing amino acids are essential amino acids.

Aminotransferase enzymes require pyridoxal phosphate as a co-enzyme.

The average man has a store of about 1kg of free amino acids.

. Which metabolic abnormality gives rise to the serious disease phenylketonuria?

Homocysteine cannot be converted into methionine.

Phenylalanine cannot be converted into tyrosine.

Phenylalanine cannot be converted into alanine.

Tyrosine cannot be converted into phenylalanine.

. Which of the following statements about the deamination of amino acids is correct?

Most amino acids are directly deaminated by dehydrogenation reactions.

Most amino acids are deaminated by a two-step transdeamination process.

Most amino acids are deaminated by transferring their amino groups to oxaloacetate.

Most amino acids are deaminated by irreversible transamination reactions.

. Which of the following statements about the mechanism of transamination reactions is correct?

ATP hydrolysis is used to transfer the amino group on the Schiff base to the carbonyl group of keto acid acceptor.

The first step of a transamination reaction is the formation of a Schiff base between pyridoxal-5'-phosphate and the carbonyl group of the keto acid.

The first step of a transamination reaction is the formation of a Schiff base between the carbonyl group of pyridoxal-5'-phosphate and the amino group of the amino acid.

The first step of a transamination reaction is the formation of a Schiff base between pyridoxamine phosphate and the keto acid.

. Which of the following statements about the carbon skeletons of amino acids are correct? Please select all that apply.

Ketogenic amino acids can give rise to acetyl-CoA.

Glucogenic amino acids can give rise to glucose in starvation.

Ketogenic amino acids give rise to glucose.

Ketogenic amino acids are always converted to ketone bodies.

Some amino acids are both glucogenic and ketogenic.

. Which of the following conditions are associated with the appearance of the childhood protein energy malnutrition known as kwashiorkor? One or more may apply.

Infection.

Oedema.

Emaciation.

Poor immune system.

. What makes an amino acid 'essential'?

If it is necessary for the structure of a protein.

If it is a necessary component of a metabolic pathway.

If its carbon skeleton cannot be synthesised by the body.

If it can be converted into glucose by gluconeogenesis.

. One of the amino groups in urea comes from free ammonia or ammonium ion usually released by glutamine in the liver. What is the origin of the second amino group?

Aspartate.

Alanine.

Arginine.

Citrulline.

Chapter 18 Self-test questions

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