Cell Biology Exam #3-2013
Name____Key_________________
Lab Section__________________
Multiple choice. Choose the best answer (2 points each)
1.___D__Which of the following statements is true? a) rough strains of Streptococcus pneumonia are
pathogenic; b) rough strain of Streptococcus pneumonia produce capsules; c) Hershey and Chase were
the first researchers to demonstrate the phenomenon of bacterial transformation; d) the combination
of heat killed smooth and living rough Streptococcus pneumonia was pathogenic to mice; e) rough
strains of Streptococcus pneumonia can evade a mouse’s immune system.
2. ___C__ In molecular biology, what is significant about the year 1953? a) the human genome project
was completed b) the process of transformation was discovered c) Watson and Crick published the
“Double Helix” paper of DNA structure d) Rosalind Franklin was born e) proteins were discovered.
3.___D__ The elongation of the leading strand during DNA synthesis
a) occurs in the 3' → 5' direction. b) progresses away from the replication fork. c) produces Okazaki
fragments. d) depends on the action of DNA polymerase. e) does not require a template strand.
4.___B__Cytosine makes up 28% of the nucleotides in a sample of DNA from an organism.
Approximately, what percentage of the nucleotides in this sample will be thymine?
a) 14; b) 22; c) 28; d) 72; e) none of the above.
5.___B__ What kind of molecule or substance is the primer that is used to initiate the synthesis of a new
DNA strand?
a) DNA; b) RNA; c) protein; d) phosphate; e) sulfur
6.__C___ Messelson and Stahl: a) conducted experiments that supported the hypothesis that DNA
replication is conservative; b) worked with DNA molecules that were labeled with P-32 and -S35;
c)were able to distinguish between parental and newly made DNA strands based upon their different
densities; d) determined that DNA was the genetic information; e) obtained their data from
transformation experiments.
7. ___A__ Excision repair mechanisms operate in the cell to: a) repair T-T dimers; b) correct errors that
occur during DNA replication; c) remove RNA primers from DNA; d)transcribe DNARNA;
e) prevent proteins from being degraded (turning over)
8.__D___ The last sentence in Watson and Crick’s paper about the structure of DNA commented: a) on
the complementary base pairing of the nucleotides A and T b) about how genotype determines
phenotype c) that Franklin had stolen some of their valuable data d)that the structure they proposed
suggested a possible mechanism of DNA replication
9.___B__ As DNA is being unwound during DNA replication, these bonds are being broken:
a) phosphodiester; b) hydrogen; c) covalent; d) ionic
10.___B__ T2 phages with S-35 labeled protein and P-32 labeled DNA were used by these
Individuals to demonstrate that DNA was the genetic information: a) A) Frederick Griffith B) Alfred
Hershey and Martha Chase C) Oswald Avery, Maclyn McCarty, and Colin MacLeod D) Erwin
Chargaff E) Matthew Meselson and Franklin Stahl
11.__C___ E. coli cells grown on N15 medium are transferred to N14 medium and allowed to grow for two
more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What
density distribution of DNA would you expect in this experiment?
a) one high-density and one low-density band
b) one intermediate-density band
c) one low-density and one intermediate-density band
d) one low-density band
e) one high-density and one intermediate-density band
12.__C___ Which of the following statements about DNA polymerase is false? a) it only will add
nucleotides to the new DNA strand in the 5'-3' direction; b) there must be a free 3'OH group available
for the enzyme to add a nucleotide on to; c) it is responsible for joining Okasaki fragments together; d) it
synthesizes one strand in a continuous fashion and the other in a discontinuous manner; e) none of the
above are false.
13.___D__This feature of DNA replication contributes to replication being a speedy process:
a) replication is bidirectional; b) multiple “replication bubbles” can form on the same DNA molecule;
c) enzymes are involved in this process; d) all of the above.
14.___D__ At a specific area of a chromosome, the sequence of nucleotides below is present where the
chain opens to form a replication fork: 3' C C T A G G C T G C A A T C C 5'
An RNA primer is formed starting at the underlined T (T) of the template. Which of the following
represents the primer sequence?
A) 5' G C C T A G G 3'
B) 3' G C C T A G G 5'
C) 5' A C G T T A G G 3'
D) 5' A C G U U A G G 3'
E) 5' G C C U A G G 3'
15.__B___ Which of the following is not a part of the eukaryotic transcription initiation complex? a)
TATA box b) splicesome c) RNA polymerase d) transcription factors e) promoter
16.___D__The sickle cell gene: a) causes sickle cell anemia if the individual is heterozygous; b) is always
harmful; c) is a dominant allele; d) confers resistance to malaria in the heterozygous state; e) codes for a
malarial parasite.
17.___A__ Replication of the leading and the lagging strands of DNA differ in that:
A) the leading strand is synthesized in the same direction as the movement of the replication fork, and
the lagging strand is synthesized in the opposite direction.
B) the leading strand is synthesized by adding nucleotides to the 3' end of the growing strand, and the
lagging strand is synthesized by adding nucleotides to the 5' end.
C) the lagging strand is synthesized continuously, whereas the leading strand is synthesized in short
fragments that are ultimately stitched together.
D) the leading strand is synthesized at twice the rate of the lagging strand.
18.__C___ A normal gene contained 348 nucleotides and its mutated counterpart also had 348
nucleotides (a base-pair substitution has occurred). However, the polypeptide coded for by the normal
gene contains 116 amino acids while the polypeptide coded for by the mutated gene has only 57 amino
acids. Which hypothesis about the mutation that occurred that would explain these results?
a) a missense mutation has occurred; b) a stop codon has mutated into a codon for an amino acid; c) a
nonsense mutation has occurred; d) a mutation in an intron has occurred; e) all of the hypothesis are
consistent with the results.
19.__B___Totipotency refers to: a) a gene that is turned off; b) the fact that all cells (except gametes)
have all of the genetic information to make an entire organism; c) the movement of the ribosome one
codon down the m-rna during the elongation phase of translation; d) the activation of splicesomes;
e) strong promoters
20. ___A__Which of the following is NOT related to a ribosomal activity?
a) spliceosome; b) codon recognition; c) t-rna binding to the P site; d) peptide bond formation; e) t-rna
binding to the A site.
21.___D__This process occurs in the cytoplasm of eukaryotic cells and consists of initiation, elongation,
and termination: a) transcription; b) post-transcriptional modification of m-rna; c) DNA replication;
d) translation; e) point mutation
22.___A__ Xeroderma pigmentosa: a) is a condition caused by an induced mutation; b) is the result of a
spontaneous mutation; c) is a disease involving overproduction of white blood cells (a type of leukemia);
d) is the result of malfunctioning splicesomes; e)is the result of failure to add a 5’cap and a poly A tail to
m-rna.
23.___D__Which of the following statements about ribosomes is false? a) unless they are joined to an
m-rna, the large and the small ribosomal subunits are not joined to each other; b) ribosomes are made
of r-rna and protein; c) some of the ribosomal rnas are ribozymes; d) prokaryotic ribosomes are 80S
e) chromosomes contain genes for r-rna.
24.___E__ An energy (ATP/GTP) requiring step in translation of proteins: a) binding of
the tRNA anticodon to the mRNA codon in the A site; b) translocation; c) attachment of
the amino acid to its specific tRNA; d) b and c; e) all of the above.
25.____A_ There are 45 different types of these molecules that can potentially bind to the P and A sites
of ribosomes: a) t-rna; b) r-rna; c) promoters; d) aminoacyl trna-synthesase; e) snRNA
26.___D__ Transcription in eukaryotes requires which of the following in addition to RNA polymerase?
a) the protein product of the promoter; b) start and stop codons; c) ribosomes and tRNA ; d) several
transcription factors (TFs); e) aminoacyl synthetase
27.__E___This is a known exception to the Central Dogma: a) totipotency; b) in some virus 12,000
nucleotides codes for more than 4,000 codons; c) in a given cell, some genes may be turned on while
other are turned off; d)transformation; e) Retrovirus (HIV)
28.___B__ Which of the following types of mutation, resulting in an error in the mRNA just after the
AUG start of translation, is likely to have the most serious effect on the polypeptide product?
a) a deletion of a codon; b) a deletion of 2 nucleotides; c) a substitution of the third nucleotide in an ACC
codon; d) a substitution of the first nucleotide of a GGG codon; e) an insertion of a codon
29.___C__ Each of the following options is a modification of the sentence THECATATETHERAT. Which of
the following is analogous to a single point mutation?
A) THERATATETHECAT
B) THETACATETHERAT
C) THECATARETHERAT
D) THECATATTHERAT
E) CATATETHERAT
30.___D__If a bacterium shows a positive Ames test after exposure to chemical X, then: a) chemical X is
definitely a carcinogen; b) chemical X will cause tumors in rats; c) chemical X is a substance that
stimulates gene expression; d) chemical X is a mutagen; e) all of the above are correct.
31. (4 points each) Agree or disagree with the following statements. In either case, fully defend your
position.
A. From his transformation experiments, Griffith was able to determine that DNA and not protein was
the genetic information.
Disagree-Griffith was able to demonstrate that living rough cells were transformed into living cells
smooth cells by being taking up genetic information from heat killed smooth cells , but he did not
identify what the transforming substance was. Avery,McCloud, and McCarty later identified DNA as
the transforming substance.
B. The fact that DNA is antiparallel makes the process of DNA replication more complex than Watson
and Crick had envisioned.
Agree-Because DNA is antiparallel and DNA polymerase only works in the 5’3’ direction, both
strands cannot be replicated in a continuous fashion as Watson and Crick had envisioned. They were
unaware that one strand (leading strand) was made continuously and the other strand (lagging
strand) discontinuously.
C. There is a potential benefit to the genetic code being redundant.
Agree-point mutations are often negative because they change a codon so that one amino acid is
substituted for another. This may negatively affect the tertiary structure of the polypeptide coded for
by the gene. Because the code is redundant, a point mutation (especially in the third nucleotide of
the codon, may not change amino acid coded for, meaning a wild type polypeptide would still be
formed.
32. (20 points).
Answer any 2 of the following 3 essays (10 points
each):
A. (10 points) Pick 5 proteins (including enzymes) that are involved in DNA replication. In
addition to naming these proteins describe their function (role) in DNA replication.
1. Helicase (unwindase) separates the double helix so replication can begin
2. Single strand binding proteins-keeps two strands apart during replication
3. Topoisomerase-untangles kinks that develop in the bonded portion of the double helix as the
bottom portion is unwinding
4. RNA primase-add RNA nucleotides that prime the synthesis of new DNA strands
5. DNA polymerase-the enzyme that copies DNA templates in the 5’--.3’ direction, also removes
and replaces primer RNA nucleotides.
6. DNA ligase-joins Okasaki fragment together after their RNA primers have been removed and
replaced with DNA nucleotides.
B. (10 points) What are introns and exons? What is the advantage of a gene containing introns?
Using the terms snRNPs and splicesome, explain how introns are removed from m-rna. Where
does RNA splicing occur?
Introns are non coding DNA found within a gene. They do not specify amino acids sequences for a
polypeptide chain. Exons are coding DNA . They do specify amino acids sequences for a polypeptide
chain.
If a gene contains introns, as the introns are cut out during m-rna processing, the exons can be
re-spliced together in several different ways to form many different m-rna from the same gene
(alternative splicing). This is how only 500 antibody genes can code for billions of different antibody
proteins.
This RNA splicing happens in the nucleus. Here, small nuclear RNa (snRNA) associated with proteins
to form complexes called SNRPs. Several SNRPs associate with one another and other proteins to
form a molecular machine that cuts out the introns and splices the exons together. These molecular
scissors (splicesomes) are able to identify the intorn/exon boundary, loop out the intron portion of
the message, and accurately splice together the exons to make a functional m-rna.
(10 points) Starting with the gene (DNA) shown below:
gene startsATGTATACGGATgene stops
a) show the mRNA molecule that would be transcribed from this gene.
M-RNA =UACAUAUGCCUA
b) If that mRNA was translated and the following amino acids were present (amino acids are
represented by their anticodon and the amino acid the tRNA carries), show the sequence (primary
structure) of the polypeptide that would be synthesized from this mRNA
AUG/lysine; ATG/leucine; TAT/alanine; UAU/histidine; GTU/valine;
CUA/glutamine; ACG/tyrosine; UAC/aspartic acid; GAT/cysteine; UGC/serine;
GAU/isoleucine; AUA/proline
Polypeptide= lysine-histidine-tyrosine-isoleucine
33. ( 8 points) Answer the following questions from the in-class video we saw titled the Cancer Warrior.
You can come up to the front of the class and get your video notes to answer this question.
A. What is angiogenesis? How does phenomenon relate to cancer?
Won’t be on final exam
B.Why did Folkman’s lab develop a high volume urine collection system for rats that had large primary
tumors. Did this line of research lead to finding an angiogenesis inhibitor?
Won’t be on final exam