Biology 303 EXAM III 11/18/04
NAME____________________________
This exam consists of 40 questions worth 2.5 points each. Please indicate the single best
choice for each question on the separate answer sheet. Be sure to enter your student
number on the answer sheet. Good luck!
______________________________________________________________________________
1.
With regard to eukaryotic chromatin, when one visualizes "beads-on-a-string" each bead
is actually a
1. gene.
2. histone.
3. nucleosome particle.
4. 30 nanometer fiber.
2.
In eukaryotic chromatin, the next highest level of organization above "beads-on-a-string"
is
1. the “solenoid” (30 nm fiber)
2. chromatin loops.
3. the nuclear matrix.
4. the metaphase chromosome.
3.
What is the general term given to enzymes that control supercoiling?
1. topoisomerases
2. unwindases
3. nucleases
4. helicases
4.
Most DNA occurring in nature is
1.
2.
3.
4.
relaxed.
positively supercoiled.
negatively supercoiled.
not complexed with proteins
5.
“Alu” repetitive sequences are
1.
2.
3.
4.
6.
LINES
SINES
considered to be tandem repeats
a type of satellite sequence
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.
7.
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
8.
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
9.
Analysis of eukaryotic genomes has revealed that
1.
2.
3.
4.
large segments of genomes have undergone duplication during evolution.
genes are never found within the introns of other genes.
genome size always correlates well with organism complexity.
transposons are rarely found in genomes.
10.
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.
11.
The histone gene cluster:
1.
2.
3.
4.
12.
is present in multiple copies in most eukaryotes.
is identical in all eukaryotes.
contains many introns.
all of the above.
The alpha and beta globin gene families
1.
2.
3.
4.
13.
protein-coding genes.
ribosomal RNA genes.
transposons or transposon-like elements.
satellite sequences.
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.
"Satellite" sequences
a. get their name from their abundance.
b. are located primarily in the introns of genes.
c. are highly repetitive.
d. have been best characterized in bacteria.
14.
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.
15.
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.
16.
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.
17.
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.
18.
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
19.
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
20.
How many different codons do not code for an amino acid?
1. 0
2. 20
3. 3
4. 61
21.
In eukaryotes, mRNA is transcribed by
1. RNA polymerase I
2. RNA polymerase II
3. RNA polymerase III
4. none of the above.
22.
The protein-synthesizing "machine" in prokaryotes and eukaryotes is called the
1. episome.
2. ribosome.
3. chromosome.
4. nucleolus.
23.
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.
24.
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
25.
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.
26.
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.
27.
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
28.
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.
29.
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.
30.
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.
31.
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 32 and 33.
(I = lac repressor gene; Z, Y, A = lac operon structural genes; P = lac promoter; O = lac
operator)
I
P
O
Z
Y
A
32. 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
33. 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
34.
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.
35.
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.
36.
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.
4. is an example of overexpression of an oncogene that is otherwise unaltered.
37.
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.
38.
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
39.
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
40.
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
ANSWER KEY
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CORRECT ANSWER
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