Mechanisms of toxicity

Question 1

The severity of a toxin depends in a large part on the concentration of the toxin at its site of action. Which of the following will decrease the amount of toxin reaching its site of action?

a. absorption across skin
b. excretion via the kidneys
c. toxication
d. reabsorption across intestinal mucosa
e. discontinuous endothelial cells of hepatic sinusoids

Answer 1

b. excretion via the kidneys

Question 2

Toxicaton or (metabolic activation) is the biotransformation of a toxin to a more toxic and reactive species. Which of the following is not a reactive chemical species commonly formed by toxication?

a. electrophiles
b. nucleophiles
c. superoxide anions
d. hydroxy radicals
e hydrophilic organic acids

Answer 2

E. hydrophilic organic acids

Question 3

Which of the following is not an important step in detoxification of chemicals?

a. formation of redox-active reactants
b. reduction of hydrogen peroxide by glutathione peroxidase
c. formation of hydrogen peroxide by superoxide dismutase
d. reduction of glutathione disulfide (GSSG) by glutathione reductase (GR)
e. conversion of hydrogen peroxide to water and molecular oxygen by catalase.

Answer 3

a. formation of redox-active reactants

Question 4

Regarding the interaction of the ultimate toxicant with its target molecule, which of the following is false?

a. Toxins often oxidize or reduce their target molecules, resulting in the formation of a harmful byproduct
b. The covalent binding of a toxin with its target molecule permanently enters the target’s function
c. The non covalent binding of a toxin to an ion channel irreversibly inhibits ion flux thru the channel
d. Abstraction of Hydrogen atoms from endogenous compounds by free radicals can result in the formation of DNA adducts
e. Several toxins can act enzymatically on their specific target proteins

Answer 4

c. The non covalent binding of a toxin to an ion channel irreversibly inhibits ion flux thru the channel

Question 5

All of the following are common effects of toxicants on target molecules EXCEPT:

a. blockage of neurotransmitter receptors
b. interference with DNA replication due to adduct formation

c. cross-linking of endogenous molecules
d. opening ion channels
e. mounting an immune response

Answer 5

d. opening ion channels

Question 6

Which of rh following proteins functions to prevent the progression of the cell cycle?

a. NF-kB
b. MAPK
c. CREB
d. c-Myc
e. IkB

Answer 6

e. IkB

Question 7

Which of the following would have the largest negative impact on intracellular ATP levels

a. moderately decreased caloric intake
b. interference with electron delivery to the electron transport chain
c. inability to harvest ATP from glycolysis
d. increased synthesis of biomolecules
e. active cell division

Answer 7

b. interference with electron delivery to the electron transport chain

Question 8

What happens when a toxin induce elevation of cytoplasmic calcium levels?

a. Mitochondrial uptake of calcium dissipates the electrochemical gradient needed to synthesize ATP.
b. Formation of actin filaments increases the strength and integrity of the cytoskeleton
c. It increases the activity of intracellular proteases, nucleases, and phospholipase
d. The cell becomes. dormant until the calcium is actively pumped from the cell.
e. The generation of reactive oxygen species slows because of calcium-induced decrease in activity of the TCA cycle

Answer 8

a. Mitochondrial uptake of calcium dissipates the electrochemical gradient needed to synthesize ATP.

Question 9

Cytochrome c is an important molecule in initiating apoptosis in cells. All of the following regarding cytochrome c are true EXCEPT:

a. The release of cytochrome c into the cytoplasm is an important step in apoptosis initiation.
b. The loss of cytochrome c from the electron transport chain blocks ATP synthesis by oxidative phosphorylation
c. Loss of cytochrome c from the inner mitochondrial membrane results in increased formation of reactive oxygen species
d. Bax proteins mediate cytochrome c release
e. Capsases are proteases that increase cytoplasmic levels of cytochrome c

Answer 9

e. Capsases are proteases that increase cytoplasmic levels of cytochrome c

Question 10

All of the following regarding DNA repair are true EXCEPT:

a. In a lesion that does not cause a major distortion of the double helix, the incorrect base is cleaved and the correct base is inserted in its place
b. Base excision repair and nucleotide excision repair are both dependent on a DNA polymerase and a DNA ligase
c. In nucleotide excision repair, only the adduct is cleaved, and the gap is then filled by DNA polymerase
d. Pyrimidine dimers can be cleaved and repaired directly by DNA photolyase
e. Recombinational repair requires that a sister strand serve as a template to fill in missing nucleotides

Answer 10

c. In nucleotide excision repair, only the adduct is cleaved, and the gap is then filled by DNA polymerase

Question 11

Apoptosis can serve as a tissue repair process in a number of cell types. In which of the following cell types would this be a plausible mechanism of tissue repair?

a. female germ cells
b. gastrointestinal epithelium
c. neurons
d. retinal ganglion cells
e. cardiac muscle cells

Answer 11

b. gastrointestinal epithelium

Question 12

Which of the following is NOT associated with carcinogenesis?

a. mutation
b. normal p53 function
c. Rax activation
d. inhibition of apoptosis
e. DNA repair failure

Answer 12

b. normal p53 function