04-29-2008, 09:06 PM
11. A farming couple in Northern Michigan consult their physician about severe skin rashes and ulcers noted over the past year. They also have lost many cattle over the past year, and claim that their cattle feed changed in consistency and smell about 1 year ago. Chemical analysis of the feed shows high concentrations of polychlorinated biphenyls, a fertilizer related to known carcinogens. The physician sends the chemical to a laboratory for carcinogen testing, which is performed initially and rapidly by
a. Inoculation of the chemical into nude mice
b. Incubation of mutant bacteria with the chemical to measure the rate of reverse or œback mutations
c. Incubation with stimulated white blood cells to measure the impact on DNA replication
d. Computer modeling based on the structures of related carcinogens
e. Incubation with mammalian cell cultures to measure the rates of malignant transformation
12. A child presents with severe growth failure, accelerated aging that causes adult complications such as diabetes and coronary artery disease, and microcephaly (small head) due to increased nerve cell death. In vitro assay of labeled thymidine incorporation reveals decreased levels of DNA synthesis compared to controls, but normal-sized labeled DNA fragments. The addition of protein extract from normal cells, gently heated to inacti¬vate DNA polymerase, restores DNA synthesis in the child™s cell extracts to normal. Which of the enzymes used in DNA replication is likely to be defective in this child?
a. DNA-directed DNA polymerase
b. Unwinding proteins
c. DNA polymerase I
d. DNA-directed RNA polymerase
e. DNA ligase
a. Inoculation of the chemical into nude mice
b. Incubation of mutant bacteria with the chemical to measure the rate of reverse or œback mutations
c. Incubation with stimulated white blood cells to measure the impact on DNA replication
d. Computer modeling based on the structures of related carcinogens
e. Incubation with mammalian cell cultures to measure the rates of malignant transformation
12. A child presents with severe growth failure, accelerated aging that causes adult complications such as diabetes and coronary artery disease, and microcephaly (small head) due to increased nerve cell death. In vitro assay of labeled thymidine incorporation reveals decreased levels of DNA synthesis compared to controls, but normal-sized labeled DNA fragments. The addition of protein extract from normal cells, gently heated to inacti¬vate DNA polymerase, restores DNA synthesis in the child™s cell extracts to normal. Which of the enzymes used in DNA replication is likely to be defective in this child?
a. DNA-directed DNA polymerase
b. Unwinding proteins
c. DNA polymerase I
d. DNA-directed RNA polymerase
e. DNA ligase