BIOCHEM BRS EXAM QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS VERIFIED
A bacterial mutant grows normally at 32°C but at 42°C accumulates short
segments of newly synthesized DNA. Which one of the following enzymes is most
likely to be defective at the nonpermissive temperature (the higher temperature)
in this mutant?
(A) DNA primase
(B) DNA polymerase
(C) An exonuclease
(D) An unwinding enzyme (helicase)
(E) DNA ligase
(E) DNA ligase
An RNA produced from a fragment of DNA has the sequence of AAUUGGCU. The
sequence of the nontemplate strand in the DNA that gave rise to this sequence is
which one of the following?
(A) AGCCAATT
(B) AAUUGGCU
(C) AATTGGCT
(D) TTAACCGA
(E) UUAACCGA
(C) AATTGGCT
,Which one of the following changes in the coding region of an mRNA (caused by
a point mutation) would result in translation of a protein identical to the normal
protein?
(A) UCA → UAA
(B) UCA → CCA
(C) UCA → UCU
(D) UCA → ACA
(E) UCA → GCA
(C) UCA → UCU
Gene transcription rates and mRNA levels were determined for an enzyme that is
induced
by glucocorticoids. Compared with untreated levels, glucocorticoid treatment
caused a 10-fold increase in the gene transcription rate and a 20-fold increase in
both mRNA levels and enzyme activity. These data indicate that a primary effect
of glucocorticoid
treatment is to decrease which one of the following?
(A) The activity of RNA polymerase II
(B) The rate of mRNA translation
(C) The ability of nucleases to act on mRNA
(D) The rate of binding of ribosomes to mRNA
(E) The rate of transcription
(C) The ability of nucleases to act on mRNA
,A temperature-sensitive cell line would show early senescence when grown at the
nonpermissive temperature, and examination of the chromosomes demonstrated
many 3′ overhangs at the ends of the DNA fragments. The defective enzyme, at
the nonpermissive temperature, is which one of the following?
(A) Telomerase
(B) DNA ligase
(C) DNA polymerase
(D) A repair DNA polymerase
(E) A helicase
(A) Telomerase
A family, while on a picnic, picked some wild mushrooms to add to their picnic
salad. Shortly thereafter, all the members of the family became ill, with the
youngest child showing the most severe symptoms. The family is suffering these
effects owing to a primary inability to accomplish which one of the following in
their cells and tissues?
(A) Synthesize proteins
(B) Synthesize lipids
(C) Synthesize DNA
(D) Synthesize carbohydrates
(E) Repair damage in DNA
(A) Synthesize proteins
A newborn has found to be very photophobic, and his skin burns even with
minimal exposure to sunlight, eventually forming skin blisters. Neither parent
, exhibits this trait, although both are prone to burning when in the sun for a short
period of time. As the child grows, he is found to be at average height and weight
for his age, and is progressing normally along the developmental guidelines. He
is, however, kept inside at all times, and is carefully wrapped if he has to leave
the house. Fibroblasts isolated from this child are grown in culture, and in an
experiment, exposed to
UV light. An analysis of the fibroblast DNA will demonstrate which one of the
following?
(A) A preponderance of apurinic sites and apyrimidinic sites
(B) An increase in sister chromatid exchange rate
(C) A preponderance of abnormal base pairs in the DNA
(D) Loss of telomeres within the DNA
(E) An increase in cross-linked bases within the strands of DNA
(E) An increase in cross-linked bases within the strands of DNA
A 15-year-old boy was diagnosed with skin
cancer. He had always been sensitive to sunlight,
and had remained indoors for most of his life. An analysis of his DNA, from
isolated fibroblasts, indicated an increased level of thymine dimers when the
cells were exposed to UV light. The boy developed a skin tumor owing to an
increased mutation rate, which was caused by which one of the following?
(A) A lack of DNA primase activity
(B) Decreased recombination during mitosis
(C) Increased recombination during mitosis
COMPLETE SOLUTIONS VERIFIED
A bacterial mutant grows normally at 32°C but at 42°C accumulates short
segments of newly synthesized DNA. Which one of the following enzymes is most
likely to be defective at the nonpermissive temperature (the higher temperature)
in this mutant?
(A) DNA primase
(B) DNA polymerase
(C) An exonuclease
(D) An unwinding enzyme (helicase)
(E) DNA ligase
(E) DNA ligase
An RNA produced from a fragment of DNA has the sequence of AAUUGGCU. The
sequence of the nontemplate strand in the DNA that gave rise to this sequence is
which one of the following?
(A) AGCCAATT
(B) AAUUGGCU
(C) AATTGGCT
(D) TTAACCGA
(E) UUAACCGA
(C) AATTGGCT
,Which one of the following changes in the coding region of an mRNA (caused by
a point mutation) would result in translation of a protein identical to the normal
protein?
(A) UCA → UAA
(B) UCA → CCA
(C) UCA → UCU
(D) UCA → ACA
(E) UCA → GCA
(C) UCA → UCU
Gene transcription rates and mRNA levels were determined for an enzyme that is
induced
by glucocorticoids. Compared with untreated levels, glucocorticoid treatment
caused a 10-fold increase in the gene transcription rate and a 20-fold increase in
both mRNA levels and enzyme activity. These data indicate that a primary effect
of glucocorticoid
treatment is to decrease which one of the following?
(A) The activity of RNA polymerase II
(B) The rate of mRNA translation
(C) The ability of nucleases to act on mRNA
(D) The rate of binding of ribosomes to mRNA
(E) The rate of transcription
(C) The ability of nucleases to act on mRNA
,A temperature-sensitive cell line would show early senescence when grown at the
nonpermissive temperature, and examination of the chromosomes demonstrated
many 3′ overhangs at the ends of the DNA fragments. The defective enzyme, at
the nonpermissive temperature, is which one of the following?
(A) Telomerase
(B) DNA ligase
(C) DNA polymerase
(D) A repair DNA polymerase
(E) A helicase
(A) Telomerase
A family, while on a picnic, picked some wild mushrooms to add to their picnic
salad. Shortly thereafter, all the members of the family became ill, with the
youngest child showing the most severe symptoms. The family is suffering these
effects owing to a primary inability to accomplish which one of the following in
their cells and tissues?
(A) Synthesize proteins
(B) Synthesize lipids
(C) Synthesize DNA
(D) Synthesize carbohydrates
(E) Repair damage in DNA
(A) Synthesize proteins
A newborn has found to be very photophobic, and his skin burns even with
minimal exposure to sunlight, eventually forming skin blisters. Neither parent
, exhibits this trait, although both are prone to burning when in the sun for a short
period of time. As the child grows, he is found to be at average height and weight
for his age, and is progressing normally along the developmental guidelines. He
is, however, kept inside at all times, and is carefully wrapped if he has to leave
the house. Fibroblasts isolated from this child are grown in culture, and in an
experiment, exposed to
UV light. An analysis of the fibroblast DNA will demonstrate which one of the
following?
(A) A preponderance of apurinic sites and apyrimidinic sites
(B) An increase in sister chromatid exchange rate
(C) A preponderance of abnormal base pairs in the DNA
(D) Loss of telomeres within the DNA
(E) An increase in cross-linked bases within the strands of DNA
(E) An increase in cross-linked bases within the strands of DNA
A 15-year-old boy was diagnosed with skin
cancer. He had always been sensitive to sunlight,
and had remained indoors for most of his life. An analysis of his DNA, from
isolated fibroblasts, indicated an increased level of thymine dimers when the
cells were exposed to UV light. The boy developed a skin tumor owing to an
increased mutation rate, which was caused by which one of the following?
(A) A lack of DNA primase activity
(B) Decreased recombination during mitosis
(C) Increased recombination during mitosis
