ANSWER KEY
Here are some sample questions to help you prepare for Exam III. Your real exam will
consist of 40 multiple choice questions as usual. As always, if you have a question, or
if an answer seems wrong, please contact me. Questions marked with asterisks (*) are
on material that WILL NOT be covered on your exam.
1.
Each of the following describes a property of the genetic code EXCEPT:
1. it's unambiguous.
2. it's overlapping.
3. it's present in mRNA.
4. it uses nucleotide triplets.
2.
The genetic code is said to be “degenerate” because
1. there are more codons than amino acids.
2. there are more amino acids than codons.
3. different organisms use different codons to encode the same amino acid.
4. it frequently goes on drinking binges.
3.
Imagine a world in which proteins are made from 65 different amino acids.
Assume that in this imaginary world the genetic code is nonoverlapping and utilizes the
smallest possible size for a codon that accommodates all amino acids unambiguously.
In this particular world, which of the following mutations in the coding region of a gene
would not cause a frame-shift?
1. an insertion of 2 nucleotides
2. an insertion of 3 nucleotides.
3. a deletion of 8 nucleotides
4. a deletion of 5 nucleotides.
4.
Which of the following is true?
1. the second position in a triplet accounts for most degeneracy in the genetic
code.
2. two gene sequences can overlap on a chromosome.
3. there are more types of tRNA molecules than there are different codons.
4. the genetic code is used only in eukaryotes.
5.
The first step in the transfer of protein-coding information present on one of the
two DNA strands is the production of a complementary RNA molecule. What is this
RNA molecule termed?
1. ribosomal RNA
2. operator RNA
3. messenger RNA
4. transfer RNA
6.
What is the term for the triplet sequence in tRNA that is complementary to an
mRNA codon?
1. attenuator
2. anticodon
3. Shine-Dalgarno sequence
4. promoter
7.
How many different codons do not code for an amino acid?
1. 0
2. 20
3. 3
4. 61
8.
In eukaryotes, mRNA is transcribed by
1. RNA polymerase I
2. RNA polymerase II
3. RNA polymerase III
4. none of the above.
9.
The protein-synthesizing "machine" in prokaryotes and eukaryotes is called the
1. episome.
2. ribosome.
3. chromosome.
4. nucleolus.
10.
Which is not a feature of a typical tRNA molecule?
1. it consists of only the usual bases A,U,C,G.
2. it is likely to be less than 100 bases in length.
3. it can get "charged" by an aminoacyl tRNA synthetase.
4. it is often depicted in a “cloverleaf” configuration.
11.
The special DNA sequence that helps translation to initiate at the right place in
bacteria is called
1. an attenuator
2. the Shine-Dalgarno sequence.
3. the TATA box.
4. the promoter region
12.
When a stop codon is positioned at the A site of a ribosome
1. elongation of the protein being made proceeds.
2. a frameshift mutation occurs.
3. transcription initiates.
4. termination of translation occurs.
13.
A few years ago, geneticists cloned the human gene responsible for the disease
alkaptonuria. More than 90 years ago, Garrod's original studies of the disease
alkaptonuria
1. indicated that some diseases are caused by infectious agents.
2. provided very strong evidence for the one gene:one polypeptide hypothesis.
3. linked genetic defects to errors in metabolic pathways.
4. none of the above.
14.
Two mutant strains of a microorganism are auxotrophic for compound X. The
compounds A, B, and C are related to compound X. One of the mutants can grow
when fed compound A or C, but can't grow when fed compound B. The other mutant
can grow when fed compound A, but can't grow when fed compound B or C. Which of
the following may represent the biosynthetic pathway for compound X?
1. A-->B-->C-->X
2. B-->A-->C-->X
3. B-->C-->A-->X
4. C-->B-->A-->X
15.
Which statement is most accurate?
1. a typical gene encodes one enzyme.
2. a typical gene encodes one metabolic pathway.
3. a typcial gene encodes one polypeptide.
4. every RNA molecule encodes a protein.
16.
What is the term which refers to a contiguous set of bacterial genes which are
under coordinate control?
1. lysogen.
2. prototroph.
3. operon.
4. allosteric.
17.
What effect on transcription of the structural genes of the lac operon is observed
when lactose is present in the environment?
1. Transcription does not occur.
2. The genes are transcribed for only a single generation and then are shut off.
3. Lactose represses the synthesis of the repressor.
4. Transcription of the structural genes is induced when lactose is present.
18.
What is the function of cAMP in regulation of the lac operon?
1. activates a repressor protein
2. activates an activator protein
3. inactivates a repressor protein
4. inactivates an activator protein
Use the following diagram of the lac I gene and lac operon for questions 19 and 20.
(I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac
operator)
I
P
O
Z
Y
A
19. Where would the lac repressor be bound in a (nonmutant) E. coli cell that is
growing in low glucose and high lactose?
1. P
2. O
3. P and O
4. the repressor would not be bound
20. Which parts of the DNA region shown in the diagram encode proteins?
1. P
2. P, O, Z, Y, A
3. I, Z, Y, A
4. I, P, O, Z, Y, A
21.
Consider a bacterial strain that has a mutant lac repressor that cannot bind the
lac operator region. This strain likely
1. synthesizes lactose.
2. displays inducible expression of the lac operon.
3. displays constitutive expression of the lac operon.
4. does not catabolize lactose.
22.
When referring to attenuation in regulation of the tryptophan operon it would be
safe to say that when there are high levels of tryptophan available to the
organism
1. the tryptophan operon is being transcribed at relatively high levels.
2. translational termination is likely.
3. transcriptional termination is likely.
4. tryptophan is inactivating the repressor protein.
23.
What modification neutralizes the charges on histones and loosens up the
interactions between histones and DNA?
1. phosphorylation
2. demethylation
3. acetylation
4. polyadenylation
24.
In eukaryotes, mRNA is transcribed by
1. RNA polymerase I
2. RNA polymerase II Same as question 8!! Oops.
3. RNA polymerase III
4. none of the above.
25.
One form of post-translational modification of a protein might be
1. removal of introns.
2. shuffling of exons.
3. removal or modification of amino acids.
4. removal of exons.
26.
A type of DNA sequence in eukaryotes that helps to regulate transcription, may
be tissue specific, and may exert control over a structural gene that is a great
distance away is called
1. a promoter.
2. a Shine-Dalgarno sequence.
3. a TATA box.
27.
4. an enhancer.
In eukaryotes, actively transcribed chromatin is
1. DNase insensitive.
2. in a highly condensed form
3. usually DNase sensitive.
4. sometimes referred to as heterochromatin.
28.
The term "chromatin remodeling" refers to
1. alteration of chromatin structure in association with transcription.
2. a process that only bacteria perform since they contain no nucleus.
3. a process that is exclusively associated with transcription by RNA polymerase
III in eukaryotes.
4. alteration in chromatin structure to facilitate loading and translation by
ribosomes and, thus, enhance gene expression.
29.
DNA methylation may be a significant mode of genetic regulation in eukaryotes.
Methylation refers to
1. altering RNA polymerase activity by methylation of RNA polymerase
2. altering translational activity especially of highly methylated tRNAs.
3. alteration of DNA polymerase activity by addition of methyl groups to glycine
residues.
4. addition of methyl groups to the cytosine of CG doublets
30.
The phenomemon known as “RNAi” (RNA interference) is used experimentally to
1.
2.
3.
4.
31.
reduce expression of a specific target gene.
reduce transcription rate from a specific gene promoter.
interfere with replication.
enhance gene expression.
The "Philadelphia chromosome"
1. is a movie starring Tom Hanks.
2. is a specific translocation implicated in chronic myelogenous leukemia.
3. results from a gene amplification event.
32.
4. is an example of overexpression of an oncogene that is otherwise unaltered.
Which statement about cancer is true?
1. the development of cancer usually involves a single mutation.
2. "loss of heterozygosity" (LOH) is usually discussed in relation to tumor
suppressor genes.
3. oncogenes and proto-oncogenes are the same thing.
4. people with inherited predisposition to cancer are usually born homozygous
for a defective tumor suppressor gene.
33.
What is the name of the type of protein that combines with cyclins to exert local
control of the cell cycle?
1. cyclin dependent kinase
2. phosphatase
3. ATPase
4. telomerase
34.
An individual develops retinal tumors in both eyes. This is most likely due to
1. Wilms tumor.
2. the nonfamilial form of retinoblastoma.
3. cancer in another part of the body that has metastasized to the eye.
4. the familial form of retinoblastoma
35.
What is the name of the protein that, among other things, regulates the entry of
cells into S phase and is known as the “guardian of the genome.”
1. p34
2. p102
3. cyclin
4. p53
36*.
Regarding the sequencing of genomes, which statement is true?
1. most of the human genome has been sequenced.
2. no eukaryotic genome has yet been sequenced.
3. DNA sequencing has revealed a complete lack of polycistronic transcription
units in eukaryotic genomes.
4. eukaryotic genomes display a higher gene density than do prokaryotic
genomes.
37*.
Compared to prokaryotic chromosomes, eukaryotic chromosomes in general
1. are larger
2. have interrupted genes
3. display lower gene density
4. all of the above
38*. Based on the most recent analysis of the sequence of the human genome, which
is closest to the estimated number of human genes?
1. 3,000
2. 30,000
3. 100,000
4. 500,000
39*.
Analysis of eukaryotic genomes has revealed that
1. large segments of genomes have undergone duplication during
evolution.
2. genes are never found within the introns of other genes.
3. genome size always correlates well with organism complexity.
4. transposons are rarely found in genomes.
40.
Analysis of the human genome has revealed that about half (or maybe more) of
the human genome seems to be composed of
1.
2.
3.
4.
protein-coding genes.
ribosomal RNA genes.
transposons or transposon-like elements.
satellite sequences.
41*.
The alpha and beta globin gene families
1.
2.
3.
4.
each contain one single gene.
contain genes with no introns.
each contain one or more “pseudogenes.”
are within the heterochromatin portion of the human genome.
42.
A bacterial enzyme that cuts DNA within a short, specific sequence and is used
in many applications by molecular biologists is known as a
1. topoisomerase.
2. restriction enzyme.
3. polymerase.
4. glycosidase.
43.
If a geneticist wanted to view specific DNA fragments contained within a sample
of DNA from an entire eukaryotic genome, then she would probably perform a
1. Southern blot.
2. Eastern blot.
3. fluctuation test.
4. complementation test.
44*.
A geneticist wants to get a profile for the expression of thousands of specific
genes in cells isolated from a person. What tool should the geneticist use?
1.
2.
3.
4.
*
DNA chip (or array).
Southern blot.
psychic.
hammer.
Questions marked with asterisks are on material that WILL NOT be covered on
your exam.