Chapter 19 Self-test questions

. Which of the following statements about the nomenclature of nucleosides is not true?

Cytosine is a nucleoside made up of the base cytidine attached to ribose.

Adenosine is a nucleoside made up of the base adenine attached to ribose.

Thymine is a nucleoside made up of the base thymidine attached to ribose.

Inosine is a nucleoside made up of the base hypoxanthine attached to L-ribose.

. Which of the following statements about the structure of nucleotides is correct?

The sugar component of a nucleotide is always ribose.

The sugar component of a nucleotide is always deoxyribose.

The bases in nucleotides are attached to the pentose sugar moieties by a glycosidic bond.

The sugar component of a nucleotide is in the L-configuration.

. Which of the following statements about the de novo synthesis of purine nucleotides is correct?

AMP is the first purine nucleotide assembled from the de novo pathway.

The enzyme PRPP amidotransferase catalyses the committed step of the de novo synthesis pathway.

IMP is a competitive inhibitor of PRPP synthetase.

AMP is a competitive inhibitor of PRPP amidotransferase.

. Which of the following statements about the salvage pathway for the synthesis of purine nucleotides is correct?

Increased PRPP levels in cells inactivate hypoxanthine-guanine phosphoribosyl transferase (HGPRT).

Decreased PRPP levels in cells lead to the activation of hypoxanthine-guanine phosphoribosyl transferase (HGPRT).

Increased PRPP levels in cells lead to the activation of hypoxanthine-guanine phosphoribosyl transferase (HGPRT).

Purine nucleotides competitively inhibit hypoxanthine-guanine phosphoribosyl transferase (HGPRT).

. Which of the following statements about the formation of uric acid is correct?

Uric acid levels are reduced by a deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGPRT).

Uric acid levels are increased by a deficiency of hypoxanthine-guanine phosphoribosyl transferase (HGPRT).

Uric acid levels are reduced by increasing the activity of the de novo pathway.

Uric acid levels are increased by increasing the activity of the salvage pathway.

. Why is the haematological manifestation of vitamin B12 deficiency similar to that produced by tetrahydrofolate deficiency?

Deficiency of B12 prevents the removal of the methyl group of methyl tetrahydrofolate.

Deficiency of B12 leads to increased levels of methionine in the blood which affects the shape of erythrocytes.

Both vitamin deficiencies lead to microcytic anaemia because they interfere with iron uptake.

Both vitamin deficiencies lead to polycythaemia by increasing the production of erythrocytes.

. What is the mode of action of the anticancer drug methotrexate?

It inhibits the absorption of folate from the intestine.

It inhibits dihydrofolate reductase so inhibiting thymidylate synthesis.

It inhibits the secretion of extrinsic factor which is needed for DNA synthesis.

It inhibits protein synthesis at the elongation stage.

. Which of the following statements about the salvage pathway for the synthesis of purine nucleotides is correct?

The salvage pathway for the synthesis of purine nucleotides is not energetically advantageous.

The salvage pathway for the synthesis of purine nucleotides is energetically advantageous.

Salvaged purines used in the salvage pathway are mainly from the diet.

The nucleotides produced from the salvage pathway do not decrease the de novo pathway.

. Which of the following statements about uric acid is correct?

Uric acid is readily soluble in the blood.

Overproduction of PRPP leads to the formation of excess uric acid.

Uric acid is the oxidised product of purines and pyrimidines

Allopurinol is a suicide inhibitor of PRPP amidotransferase.

. Which of the following statements about one-carbon transfers reactions in purine and pyrimidine nucleotide synthesis are correct? Please select all that apply.

FH₄ (tetrahydrofolate) is used for the one-carbon transfer in purine nucleotide synthesis.

N¹⁰-formyltetrahydrofolate is used as the one-carbon donor in purine nucleotide synthesis.

Thymidylate synthase uses FH₄ (tetrahydrofolate) for the synthesis of dTMP.

N⁵-methyl FH₄ is used for the one-carbon transfer in purine nucleotide synthesis.

N⁵,N¹⁰-methylene FH₄ is used in the synthesis of dTMP from dUMP.

. What is the cause of pernicious anaemia?

A vegan diet poor in vitamin B12.

Deficiency of the glycoprotein intrinsic factor.

Deficiency of folate in the diet.

Deficiency of folate caused by drugs such as methotrexate.

. The drug allopurinol is used in the treatment of gout. How does it act?

It inhibits xanthine oxidase.

It inhibits guanine deaminase.

It inhibits the salvage pathway of purine production.

It inhibits HGPRT (hypoxanthine-guanine phosphoribosyl transferase).

Chapter 19 Self-test questions

Quiz Content