BCHM307 Exam 2 Questions With Correct Answers
1. Following is the sequence of the sense or coding strand of a particular gene. What is the amino acid sequence of the peptide encoded in this gene? Use the standard genetic code to aid you in finding an answer.
5'-GCTAGGCATGTACGCCGGTCA-3'
a. Ala-...
1. Following is the sequence of the sense or coding strand of a particular gene. What is
the amino acid sequence of the peptide encoded in this gene? Use the standard genetic
code to aid you in finding an answer.
5'-GCTAGGCATGTACGCCGGTCA-3'
a. Ala-Arg-His-Val-Arg-Arg-Ser
b. Met-Tyr-Ala-Gly-Gln-Leu-Gly
c. Met-Tyr-Tyr-Asn-Phe-His-Arg
d. None of the above - Answer-a. Ala-Arg-His-Val-Arg-Arg-Ser
/.A nuclease catalyzes a reaction in which
a. Phosphodiester bonds are hydrolyzed
b. An RNA segment is fused to a DNA segment
c. Two polynucleotide strands are twisted around each other
d. Nucleotides undergo condensation - Answer-a. Phosphodiester bonds are hydrolyzed
/.A ribosome reading along the two strands of mRNA, below translates a peptide from
each.
1.CGUAUGCUUAUAAAGUCGUAG
2.CGUAUGUUAAUAAAGUAGUCG
Immediately after translation, how many amino acid residues would the two peptides
have in common? Use the standard genetic code to aid you in finding an answer.
a. 4
b. 3
c. 6
d. 5 - Answer-a. 4
/.A variety of compounds inhibit topoisomerases. Novobiocin is an antibiotic and, like
ciprofloxacin, it inhibits DNA gyrase. Doxorubicin and etoposide are anticancer drugs
that inhibit eukaryotic topoisomerases. What properties distinguish the antibiotics from
the anticancer drugs? - Answer-Novobiocin and ciprofloxacin are useful as antibiotics
because they inhibit prokaryotic DNA gyrase but not eukaryotic topoisomerases. They
can kill disease-causing prokaryotes without harming host eukaryotic cells. Doxorubicin
and etoposide inhibit eukaryotic topoisomerases and can be used as anticancer drugs.
Although these drugs inhibit topoisomerases from both cancer cells and normal cells,
cancer cells have a higher rate of DNA replication and are more susceptible to the
effects of the inhibitors than are normal cells.
/.Addition of a(n) ___ group to certain lysine residues of a histone protein makes the
region of chromatin transcriptionally ___; addition of a(n) ___ group to certain lysine
residues makes the region of chromatin transcriptionally ___.
a. Acetyl, silent; methyl, active
,b. Methyl, highly active; acetyl, active
c. Methyl, silent; phosphate, active
d. Methyl, silent; acetyl, active
e. Phosphate, silent; methyl, active - Answer-d. Methyl, silent; acetyl, active
/.Amino acids are attached to tRNA with the help of what enzyme?
a. tRNA polymerase
b. Topoisomerase
c. Aminoacyl-tRNA synthetase
d. RNA ligase - Answer-c. Aminoacyl-tRNA synthetase
/.An antibiotic that interferes with bacterial topoisomerase activity is ___ which
specifically inhibits ___.
a. Camptothecin, type II topoisomerase
b. Novobiocin, ATPase
c. Doxorubicin, type IA topoisomerase
d. Ciprofloxacin, DNA gyrase - Answer-d. Ciprofloxacin, DNA gyrase
/.An anticodon is
a. The end of the tRNA where an amino acid is attached
b. Another name for a stop codon
c. A codon sequence that is read backwards
d. A tRNA sequence that is complementary to a codon - Answer-d. A tRNA sequence
that is complementary to a codon
/.An E. Coli has ___ replication fork(s) on its single chromosome; humans have ___
replication fork(s) on each chromosome.
a. 2, 2
b. 2, many
c. 1, 1
d. many, many
e. 1, 2 - Answer-b. 2, many
/.An mRNA codon with the sequence 5'-AGU-3' can pair with a tRNA with the anticodon
a. 5'-UCA-3'
b. 5'-AGU-3'
c. 5'-ACU-3'
d. 3'AGU-5' - Answer-c. 5'-ACU-3'
/.At low frequencies during DNA replication, an extra nucleotide may be inserted into the
DNA strand. If this occurs within a gene, what would be the effect on the protein
product?
a. Only one amino acid residue within the protein could possibly be different
b. Protein synthesis would always end at the site corresponding to the nucleotide
insertion
, c. The protein product could have multiple amino acid residue changes and could be
smaller or bigger
d. The change in the DNA sequence would have no effect on the protein product -
Answer-c. The protein product could have multiple amino acid residue changes and
could be smaller or bigger
/.Besides the obvious role of keeping DNA in a single stranded state, what do single-
strand binding proteins do?
a. Prevent supercoiling
b. Aid in the formation of hairpin structures
c. Aid DNA polymerase with DNA binding
d. Protect single strand DNA from nucleases - Answer-d. Protect single strand DNA
from nucleases
/.Chaperones are located not just in the cytosol but in the mitochondria as well. What is
the role of mitochondrial chaperones? - Answer-Mitochondria contain ribosomes that
synthesize proteins encoded by mitochondrial DNA. Like cytosolic proteins,
mitochondrial proteins require the assistance of chaperones for proper folding. Other
proteins are synthesized in the cytosol and are transported partially unfolded through
pores in the mitochondrial membranes; these proteins also require the assistance of
chaperones to fold properly once they reach their destination.
/.Condensation of the amino group of one amino acid with the carboxyl group of a
second amino acid describes a protein's ___ structure.
a. Secondary
b. Quaternary
c. Primary
d. Tertiary - Answer-c. Primary
/.Describe the ways in which a cell minimizes the incorporation of mispaired nucleotides
during DNA replication. - Answer-1) the cell contains roughly equal concentrations of
the four deoxynucleotide substrates for DNA synthesis; this minimizes the chance for an
overabundant dNTP to take the place of another or for the wrong dNTP to take the
place of a scarce dNTP. 2) DNA polymerase requires accurate pairing between the
template base and the incoming base. 3) the 3' to 5'exonuclease proofreads the newly
formed base pair. 4) the removal of the RNA primer and some of the adjacent DNA
helps minimize errors introduced by primase and by the DNA polymerase at the 5 end
of a new DNA segment. 5) DNA repair mechanisms can excise mispaired or damaged
nucleotides
/.DNA replication of the circular chromosome in E. coli begins when a protein called
DnaA binds to the replication origin on the DNA. DnaA initiates replication only when the
DNA that constitutes the DNA replication origin is negatively supercoiled. Why? -
Answer-Negatively supercoiled DNA is more easily unwound, and thus the separation of
the DNA strands occurs more easily, which facilitates the replication process.
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