Chapter 11 Multiple Choice Questions

. Which of the following isotopes is not a radioisotope?

Carbon-13

Carbon-14

Tritium

Sulphur-35

. Which of the following statements best describes radiodilution analysis?

A method of determining the ratio of unlabelled compound to labelled compound in a sample

A method of determining how much the radioactivity of a sample has decreased with time

A method of how the level of a biosynthetic intermdiate within a microbial cell

A method of determining radiochemical purity

. Which pair of isotopes are likely to result in the greatest isotope effect?

Carbon-12 and carbon-14

Carbon-12 and carbon-13

Hydrogen and deuterium

Nitrogen-14 and nitrogen-15

. Which of the following detection methods is not commonly used to detect isotopically labelled drug metabolites?

Infra red spectroscopy

Nuclear magnetic resonance spectroscopy

Scintillation counting (detection of radioactivity)

Mass spectrometry

. What problem might you foresee in labelling a drug as shown?

The isotope could be easily lost since it is exchangeable with water

The isotope could be lost as a result of a metabolic oxidation

The isotope could be lost since it is acidic

The isotope could be lost as a result of hydrolysis

. What problem might you foresee in labelling a drug as shown?

The isotope could be easily lost since it is exchangeable with water

The isotope could be lost as a result of a metabolic oxidation

The isotope could be lost since it is acidic

The isotope could be lost as a result of hydrolysis

. Which of the following statements best describes an intermediate trapping experiment?

A labelled sample of a known biosynthetic precursor is fed to a culture. An enzyme inhibitor is added to block one of the stages in the biosynthetic pathway, such that the levels of labelled biosynthetic intermediate increases in the cell and can be extracted.

A labelled sample of a known biosynthetic precursor is fed to a culture. Th culture is grown for a short period of time such that there will be more of the labelled biosynthetic intermediate present than labelled natural product.

A labelled sample of a known biosynthetic precursor is fed to a culture. An unlabelled sample of a proposed biosynthetic intermediate is then added. Some time later, the proposed intermediate is extracted from the culture to see if it is labelled.

A labelled sample of a known biosynthetic precursor is fed to a culture. An alkylating agent is added some time later that reacts with any labelled biosynthetic intermediate that might have been formed, and prevents it from being converted to the fnal product. The alkylated intermediate builds up in the cell and can be extracted

. One of the metabolites of the antiviral agent indinavir results from N-dealkylation.

Which of the following structures would be a feasible analogue aimed at preventing this metabolic reaction?

Structure A

Structure B

Structure C

Structure D

. Which of the following isotopes has the shortest half life?

Fluorine-18

Carbon-11

Tritium

Carbon-14

. What is detected during positron emission tomography (PET)?

Positrons

Electrons

Neutrons

Photons

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