Download Biology 303 EXAM III

Biology 303 EXAM III 4/19/01
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. Also, please indicate the “color” of your exam (pink,
blue, or white) in the space marked “college” at the top of 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.
What is the general term given to enzymes that control supercoiling?
1. topoisomerases
2. unwindases
3. nucleases
4. helicases
3.
Which of the following statements is true of the topology of DNA found in nature?
1. DNA is typically underwound and positively supercoiled.
2. DNA is typically underwound and negatively supercoiled.
3. DNA in nature is relaxed (no supercoiling).
4. DNA is typically overwound and positively supercoiled.
4.
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
5.
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
6.
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.
7.
protein-coding genes.
ribosomal RNA genes.
transposable elements (active or inactive).
satellite sequences.
Each of the following describes a property of the genetic code EXCEPT:
1. it's unambiguous.
2. it's overlapping.
3. it's degenerate.
4. it uses nucleotide triplets.
8.
In an imaginary world where proteins are made from 257 different amino acids, what's the
smallest possible size for a codon (coding for one amino acid) in a genetic code that
accommodates all amino acids?
1. 2 nucleotides.
2. 3 nucleotides.
3. 4 nucleotides.
4. 5 nucleotides.
9.
Which of the following is true?
1. the third position in a triplet accounts for most degeneracy in the genetic code.
2. two gene sequences cannot 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.
10.
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
11.
Both the codons UUU and UUC specify for the amino acid phenylalanine. What is the
term for this phenomenon?
1. degenerate
2. universal
3. unambiguous
4. non-overlapping
12.
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
13.
How many different codons code for an amino acid?
1. 64
2. 20
3. 3
4. 61
14.
In eukaryotes, mRNA is transcribed by
1. RNA polymerase I
2. RNA polymerase II
3. RNA polymerase III
4. none of the above.
15.
There are two main types of post-transcriptional modifications that take place in the
mRNA of eukaryotes. What are these two types of modifications?
1. The addition of a poly T sequence at the 5' end of the gene and the addition of a
poly U tail at the 3' end.
2. Addition of a poly A sequence at the 5' end and the addition of a “cap” at the 3' end of
the RNA transcript.
3. The addition of a cap at the 5' end of the transcript and the addition of a poly A
sequence at the 3' end of the message.
4. The excision of the introns and the addition of a cap to the 3' end.
16.
The protein-synthesizing "machine" in prokaryotes and eukaryotes is called the
1. episome.
2. ribosome.
3. chromosome.
4. nucleolus.
17.
Which is 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 about 100,000 bp in length.
3. it can get "charged" by an aminoacyl tRNA synthetase.
4. it usually assumes a linear configuration.
18.
The special DNA sequence that helps translation to initiate at the right place in bacteria is
called
1. an enhancer
2. the Shine-Dalgarno sequence.
3. the TATA box.
4. the promoter region
19.
After a codon which codes for an amino acid is positioned at the A site of a ribosome
1. elongation of the protein being made proceeds.
2. a nonsense mutation occurs.
3. transcription initiates.
4. termination occurs.
20.
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 metabolism.
4. none of the above.
21.
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 C, but can't grow when fed compound A or B. 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
22.
Which statement is most accurate?
1. each gene encodes one enzyme.
2. each gene encodes one metabolic pathway.
3. each gene encodes one polypeptide.
4. every mRNA molecule encodes a single protein.
23.
The lac operon
1. is present in mammals and bacteria.
2. is an example of inducible gene expression.
3. is normally expressed constitutively.
4. is an example of tissue-specific expression.
24.
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 occurs when lactose is present.
25.
When a bacterial cell is present in an environment where both lactose and glucose are
present, the glucose will be metabolized first and the lactose will be used when the stores
of glucose have been depleted. How does the bacterial cell recognize the fact that glucose
is present and turn off the transcription even when lactose is present?
1. The lac promoter binds glucose and shuts down the lac operon.
2. Glucose is a repressor molecule.
3. Catabolite-activating protein-cAMP complex is required for transcription, and its
level is low when glucose is present.
4. The CAP binding site is activated.
26.
Consider a bacterial strain that has a mutant lac repressor that cannot bind the lac operator
region. If you were to introduce into this strain a stable F' element carrying a mutant repressor
gene, the cell would likely
1. synthesize lactose.
2. display inducible expression of the lac operon.
3. display constitutive expression of the lac operon.
4. probably not catabolize lactose.
27.
In attenuation of expression of the trp operon,
1. when tryptophan is scarce, the ribosome will stall and transcription will be terminated.
2. when tryptophan is scarce, the ribosome will not stall and transcription will not be
terminated.
3. when tryptophan is abundant, the ribosome will not stall and transcription will be
terminated.
4. when tryptophan is abundant, the ribosome will stall and transcription will be
terminated.
28.
The simplest of all transposable elements is called a(n)
1. Ac element.
2. P element.
3. insertion sequence.
4. transposon.
29.
The "fusion-bridge-break" cycle, a cycle of really bizarre and unstable chromosomal
mutations first observed in corn by Barbara McClintock,
1. is related to transposition of Ds elements.
2. involves fusion of telomeres.
3. refers to fusion of centromeres.
4. was eventually discredited by Mendel.
30.
Consider a hypothetical bacterial operon encoding genes needed for the degradation of
compound X. Which statement is most likely to be true?
1. when X is abundant, the operon is off.
2. when X is abundant, the operon is on.
3. this operon displays repressible, rather than inducible, expression.
4. the mRNA produced by this operon is monocistronic.
31.
The theory of "exon shuffling" says
1. eukaryotes do not have introns.
2. only prokaryotes have exons.
3. there's no wasted DNA in a mammalian genome.
4. eukaryotic genes were built up through evolution by "mixing & matching" exons.
32.
The so-called "C-value paradox" says that
1. eukaryotes seem to have too little DNA.
2. prokaryotes seem to have too much DNA.
3. prokaryotes seem to have too little DNA.
4. there is a lot of DNA in eukaryotes that has no known
function.
33.
Enhancers can be found on either side of a gene, at some distance from a gene or
within the gene. They are termed cis regulators. What is the meaning of cis regulation?
1. genes that are adjacent to the cis-acting elements are regulated.
2. a diffusible protein product is made.
3. enhancers regulate genes on separate chromosomes.
4. intron splicing is altered
34.
In steroid hormone-regulated gene expression, the hormone binds
1. a hormone receptor after entering the cell.
2. a hormone receptor prior to entering the cell.
3. DNA directly all by itself.
4. a "hormone-responsive element" after gene expression is induced.
35.
What is the function of eukaryotic transcription factors?
1. They recognize sequences within the enhancer and promoter regions and activate
transcription.
2. They direct the mRNA from the nucleus to the cytoplasm.
3. They initiate binding to the Shine-Dalgarno sequence.
4. They serve as sequences where the RNA polymerase binds
36.
The role of the cyclinB/CDK1 complex is
1. dephosphorylation of various proteins to allow the transition from G1 into S.
2. phosphorylation of various proteins to allow the transition from G2 into M.
3. arrest the cell at the G2/M transition until the proper signals are received.
4. dephosphorylation of various proteins to allow the transition from G2 into M.
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.
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
39.
Mutations in the p53 gene have been found in a wide range of human cancers. This is
most likely due to the fact that
1. p53 is important for control of the cell cycle in very specific cell types that can spread
when they become cancerous.
2. the p53 protein can move from cell to cell, causing cancer.
3. p53 is a kinase, which can phosphorylate many different cells cycle proteins.
4. p53 is involved in cell-cycle regulation in a wide variety of human cell types.
40.
Genomic instability
1. is often a hallmark of cancer.
2. might be increased by defects in DNA repair.
3. might be increased by defects in p53.
4. all of the above.