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Molecular biology (Updated 2016) > Previous exam questions > Flashcards

Previous exam questions Flashcards

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1
Q

Myotonic dystrophy in humans is a genetic disease displaying the trait of “anticipation”. This term means that progeny of an affected individual

a. May have an earlier disease onset and more severe disease than the parent
b. May have a later disease onset with less severe disease than the parent
c. Are likely to remain phenotypically normal, and can anticipate that their own offspring will be normal
d. None of the above

A

May have an earlier disease onset and more severe disease than parent

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2
Q

In comparison with the host DNA polymerases, the HIV reverse transcriptase enzyme is truly unique in what way?

a. It makes DNA from an RNA template
b. It makes RNA from an RNA template
c. It makes DNA from a DNA template
d. It makes RNA from a DNA template

A

It makes DNA from an RNA template

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3
Q

The extent of supercoiling found in circular DNA in molecules is controlled by the activities of:

a. DNA gyrase and topoisomerase I
b. DNA helicase and topoisomerase I
c. DNA gyrase and DNA helicase
d. DNA helicase and topoisomerase II

A

DNA gyrase and DNA helicase

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4
Q

Protein synthesis can be inhibited in prokaryotes by Chloramphenicol (T/F)

A

True- Blocks peptidyl transferase reactions

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5
Q

The genome of an organism refers to all the organism’s permanently maintained, replicated nucleic acids. For all higher organisms, the genome is:

a. A mixture of dsDNA and ssRNA
b. A mixture of dsDNA and dsRNA
c. Exclusively dsDNA
d. Exclusively dsRNA

A

Exclusivly dsDNA

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6
Q

Protein synthesis can be inhibited in prokaryotes by actinomycin D

A

True- Binds to DNA preventing transcription

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7
Q

The best hypothesis describing the nature of the infectious scrapie-BSE-CJ “agent” suggests it consists of:

a. An infectious protein unrelated to the normal cell’s proteins
b. A very small (thus resistant) nucleic acid in a tough protein coat
c. An infectious protein caused by a mutation in an existing cell protein
d. An infectious protein caused by a distinct conformational change in an otherwise normal protein
e. An unknown chemical contaminant in the diet caused by improper processing methods

A

An infectious protein caused by a distinct confromational change in an otherwise normal protein

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8
Q

The structure of double-stranded DNA in a eukaryotic organism has the following featuresEXCEPT:

a. It forms a regular complex with histone proteins
b. The four nucleotide bases are on the inside of the acidic sugar-phosphate helix
c. The two DNA strands run in the same direction in the double-helical structure
d. Modification by methylation of some of the cytosine can occur in inactive genes
e. The overall dimensions of AT and GC base pairs are

similar

A

The two DNA strands run in the same direction in the double-helical structure

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9
Q

The spread of Bovine Spongiform Encephalopathy in cattle is likely due to:

a. Activation of a latent PrPsc gene by a RNA tumor virus
b. Maternal transmission of the scrapie agent (whatever it is) during fetal development in utero
c. Transmission from infected sheep by ticks
d. Transmission from mother to offspring via milk or colostrum after birth
e. Feeding cattle protein supplements derived from she

ep offal

A

Feeding cattle protein supplements derived from sheep offal

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10
Q

Protein synthesis can be inhibited in prokaryotes by puromycin

A

True- terminates translation

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11
Q

Of all the RNA synthesized in a cell, >50% is hnRNA with the potential to become mRNA. What percentage of the total cell RNA is actually mature, translatable mRNA?

a. 3-5%
b. 10-15%
c. 20-25%
d. 60-70%

A

A 3-5%

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12
Q

in a female heterozygous for the sex-linked trait, Factor VIII hemophilia, the phenotype is normal. What is the term best describing this situation, where a normal allele “covers up” the defect in another allele by causing the expression of at least some normal product?

A

complementation

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13
Q

Identify the DNA sequence component that is not shared by typical eukaryotic nuclear chromosomes and typical prokaryotic chromosomes

a. Promoter
b. Stop codon
c. Telomere
d. 5’ untranslated regions

A

Telomere

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14
Q

Which of the following would NOT be considered a part of your genome?

a. Integrated retrovirus
b. Mitochondrial DNA
c. Vaccinia virus DNA in the cytoplasm
d. Integrated transposon

A

C. Vaccinia virus DNA in the cytoplasm

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15
Q

The combined activities of DNA gyrase and topoisomerase I regulate the degree of supercoiling in circular chromosomes. A separate enzyme controls the “unwinding problem” that arises during DNA replication. This enzyme is:

a. Topoisomerase II
b. DNA bump’n grindase
c. DNA helicase
d. None of the above

A

DNA helicase

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16
Q

Retroviral reverse transcriptase (RT) differs from the DNA polymerases of prokaryotic and eukaryotic cells in several aspects. These differences include

a. RT synthesizes complementary DNA using an RNA template
b. RT can use a DNA or RNA template to synthesize DNA
c. RT uses a tRNA primer to initiate first strand synthesis of complementary DNA
d. All of the above

A

All of the above

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17
Q

Protein synthesis can be inhibited in prokaryotes by Cycloheximidine

A

False

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18
Q

Protein synthesis can be inhibited in prokaryotes by a-aminitin

A

False

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19
Q

In dsDNA, there is a molar equivalence of purine and pyrimidine bases. The presence of equimolar amounts of these bases is a direct result of:

a. Hydrophobic interactions between base-pairs
b. The proof-reading functions of DNA polymerase
c. Hydrogen-bonding between complementary base-pairs
d. Shared electron orbitals between bases

A

The hydrogen bonding between complementary base-pairs

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20
Q

AZT, a drug used to slow the progression of the human immunodeficiency virus (HIV) infection, has the chemical name 3-azido-2-deoxythymidine and the structure shown in the book. What is the mode of action of AZT?

a. Inhibits protein synthesis at the peptidyltransferase step
b. Inhibits protein synthesis at the translocase step
c. Inhibits DNA synthesis by inhibiting helicase and DNA “unwinding”
d. Inhibits DNA synthesis by terminating biosynthesis of the nascent DNA molecule

A

D. Inhibits DNA synthesis by terminating biosynthesis of the nascent DNA molecule

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21
Q

Progressive retinal atrophy in Irish setters (“rod-cone dysplasia type I”) is caused by a point mutation in the phosphodiesterase b subunit that results in an amber mutation (ie a UAG stop codon) within the coding region of the gene. This is an example of:

a. Missense mutation
b. Nonsense mutation
c. Frameshift mutation
d. Deletion mutation

A

B. Nonsense mutation

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22
Q

Which of the following RNA molecules contains a sequence element referred to as an “anticodon”

a. rRNA
b. tRNA
c. mRNA
d. snRNP

A

tRNA

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23
Q

What term would you apply to a discrete unit of DNA that encodes, or has the potential to encode, a product that contributes to the phenotype of the cell?

a. Chromosome
b. Messenger RNA
c. Enhancer element
d. Gene

A

Gene

24
Q

Protein synthesis can be inhibityed in prokaryotes by Erythoromycin (T/F)

A

True-block translocation of peptidyl-tRNA from A to P

25
Q

What sort of biochemical evidence has been used to support the hypothesis that new variant Creutzfeldt-Jakob disease in humans arose from exposure to bovine spongiform encephalopathy?

a. The patterns and extent of damage in different regions of the brains of afflicted hosts
b. The length of time involved in disease development when studied in a model system
c. The amounts, sizes, and patterns of PrP27-30 accumulating in the brains of afflicted hosts
d. A-C above have all been used
e. A-C above have never been used

A

D. all of the above

26
Q

What term refers to the point in a gene sequence at which synthesis of a primary transcript begins?

a. Promoter
b. Operator
c. Transcription start site
d. Start methionine codon

A

C Transcription start site

27
Q

Which of the following classes of enzymes plays the role of primitive “immune” response toinvading viral DNA?

a. DNA polymerase
b. Polynucleotide kinase
c. Cathepsin
d. Restriction endonuclease

A

Restriction endonuclease

28
Q

Multiple isoforms of dystrophin are made in individuals that are homozygous for the wild type dystrophin allele. Which of the following is behind this polymorphism?

a. Alternative 3’ polyadenylation
b. Rapid turnover of mis-folded protein
c. Excision at the cre-lox locus
d. Alternative splicing of the primary transcript

A

D. Alternative splicing of the primary transcript

29
Q

Which of the following statements about open reading frames (ORF) is/are true?

a. An ORF refers specifically to the translated sequences of the gene
b. The presence of an ORF identifies a gene
c. Both a and b
d. Neither a nor b

A

Neither a nor b

30
Q

DNA polymerase III is responsible for replication in prokaryotes. As it only incorporates about 500 nucleotides per second, and the E. Coli chromosome is about 4x10^6bp in length, what practical limitations does this place on the replication machinery?

a. There must be several origins of replication
b. The chromosome must be linear
c. Nascent DNA synthesis must proceed in both 5’ to 3’

and 3’ to 5’ directions

d.None of the above

A

There must be several origins of replication

31
Q

A genetic disease associated with non-sex chromosomes and which, in the heterozygous state, is expressed in only about 60% of those carrying the allele is termed:

a. Sex-linked, with 60% penetrance
b. Autosomal recessive, with 60% penetrance
c. Autosomal dominant, with 60% penetrance
d. None of the above

A

C. Autosomal dominant with 60% pertrance

32
Q

Myotonic dystrophy (MD) is a human genetic disease that displays the trait of “anticipation” and which exhibits a wide variety of seemingly unrelated symptoms. Which of the following are characteristics of the gene associated with this disease?

a. The presence of large numbers of an unstable, trinucleotide repeat sequence in the 3’ non-coding region of the gene
b. Considerable sequence similarity of coding sequences with several known protein kinase genes
c. Both a and b
d. Neither a nor b

A

C. Both a and b

33
Q

Which of the following bases are pyrimidines?

a. Adenine and cytosine
b. Adenine and guanine
c. Uracil and guanine
d. Uracil and thymidine

A

Uracil and thymidine

34
Q

indicate which of the following statement(s) regarding the “life-cycle” of a eukaryotic mRNA molecule is/are true:

a. It is made only by RNA polymerase II
b. Translation of the mRNA occurs in the nucleus
c. Splicing out of introns occurs in the cytoplasm
d. All of the above
e. None of the above

A

A: it is made only by RNA polymerase 2

35
Q

All of the following are differences between the genome organization of prokaryotes and eukaryotes EXCEPT:

a. Circular chromosomes (prokaryotes) versus linear chromosomes (eukaryotes)
b. Negatively regulated operons (prokaryotes) versus positive regulation of unlinked genes (eukaryotes)
c. Gene collinear with protein sequence (prokaryotes) versus introns separating coding sequences (eukaryotes)
d. Abundant examples of repeated DNA sequences (eukaryotes) versus mostly single copy DNA (prokaryotes)
e. Cytosine nucleotides in DNA (eukaryotes) versus hydroxymethyl cytosine (prokaryotes)

A

Cytosine nucleotides in DNA vs. hydroxymethy cytosine

36
Q

During protein synthesis, the nascent polypeptide chain (like any molecule) will be driven by entropic and free energy considerations to adopt some favorable conformation. What cellular component/complex/organelle prevents this from happening?

A

Chaperones

37
Q

n doing a paired mating test for Copper toxicosis, only 1 puppy was obtained, but it was phenotypically normal. The owner is ecstatic, now believing his bitch is suitable for breeding stock. What genotype is not a possibility for the parent of the uncertain genotype, with regard to the copper toxicosis defect?

a. Homozygous normal
b. Homozygous defective
c. Heterozygous
d. Diploid

A

B. Homozygous defective

38
Q

Eukaryotic enhancer elements can have the following properties, depending upon the particular gene(s) nder consideration:

a. Enhancers can be located 5’ to the promoter, 3’ to the termination site, or within an intron
b. It is not possible for the enhancer element associated with the gene to also affect expression of an unrelated gene
c. Enhancers bind specific DNA-binding proteins to enhance the probability of those proteins interacting with termination sequences
d. All of the above
e. none of the above

A

a. Enhancers can be located 5’ to the promoter, 3’ to the termination zone, or within an intron

39
Q

Some of the differences between the RNA polymerases of prokaryotic and eukaryotic organisms INCLUDE

a. Bacterial RNA polymerases initiate synthesis with a purine triphosphate while eukaryotic polymerases use a 7-methyl guanine cap
b. Inhibition by different drugs such as rifamycin andv lpha-amanitin
c. Multiple species of specialized RNA polymerases in eukaryotes while only a single enzyme in prokaryotes
d. Recognition by bacterial RNA polymerases of the promoter region (transcription start site) in DNA directly compared to eukaryotic RNA polymerases

A

Multiple species of specialized RNA polymerases in eukaryotes while only a single enzyme in prokaryotes

40
Q

How many of the following statements are TRUE?

I.RNA splicing in eukaryotes is necessary for most genes before a functional mRNA can be produced

II.RNA splicing can result in differential gene product expression

III.Splicing in some systems can be accomplished without a protein component

IV.Poly-A addition to the 3’-OH of a primary transcript occurs before splicing

V.Some mutations in animals are caused by DNA changes in introns which affect the splicing process

A

All of them

41
Q

Mutations can arise in DNA from all of the following mechanisms EXCEPT

a. Mispairing of tRNA TYR at a UAA codon to suppress a stop codon
b. c ncorrect base pairing during replication due to a tautomeric shift in purine/pyrimidine structure
c. X-Ray or ultraviolet light irradiation
d. Spontaneous de-amination of cytosine nucleotides
e. Methylation or ethylation of purine residues at a ring nitrogen

A

Mispairing of tRNA TYR at a UAA codon to suppress a stop codon

42
Q

How does turnover affect mRNA abundance and thus gene regulation?

a. mRNA abundance is a reflection of the rate of synthesis of mRNA for a particularbgene
b. mRNA abundance is a reflection of the rate of degradation of mRNA for a particular gene
c. Greater abundance is often associated with translation of more product for a given gene, whereas lesser abundance is usually associated with translation of less gene product
d. All of the above
e. None of the above

A

All of the above

43
Q

Genetic diseases caused by insertions or deletions of sequences within an affected gene can result in (depending upon the disease):

a. Frame-shifts
b. Premature or delayed initiation or termination of transcription or translation
c. Instability of transcripts
d. All of the above
e. None of the above

A

D: All of the above

44
Q

Congratulations! You have recently acquired the sequence of a cloned dsDNA fragment. You need to determine if there is a protein-encoding sequence present. How many reading frames must you consider?

a. One
b. Two
c. Three
d. Six

A

D. Six

45
Q

In eukaryotes, transcription of essentially any gene appears to require binding of “TATA factor”b(TFIID) to the promoter. Other transcription factors may bind here or to the enhancer, if present. Depending upon the individual factor, transcription factors can have the following characteristics:

  1. T/F They control loading of RNA polymerase II onto the promoter
  2. T/F They can regulate the expression of individual genes or even groups of genes
  3. T/F They can be expressed in a tissue-specific or developmental stage-specific manner
A

All truths

46
Q

To which of the terms below does the following definition refer? “That segment of a nucleicacid sequence that lies between two stop codons in the same reading frame, when translated in that reading frame”

a. Open reading frame
b. Reading frame
c. Intron
d. Exon

A

A.Open reading frame

47
Q

Energy input for protein synthesis includes all EXCEPT:

a. A GTP requirement for translocation during elongation (after the peptidyl transferase step)
b. An ATP requirement for the amino-acyl synthetase (tRNA charging)
c. A GTP hydrolysis to correctly bind tRNAs in the A site during elongation
d. GTP hydrolysis by peptidyl transferase during formation of the peptide bond
e. A GTP requirement for tRNA MET binding in the P site of the small subunit during initiation

A

A GTP requirement for tRNA MET binding in the P site of the small subunit during initiation

48
Q

What characteristic of the chromosomes of higher eukaryotic organisms renders the sequencing of entire genomes extremely difficult?

a. Coding sequences are a comparatively minor part of the chromosomes (eg 10-20%)
b. Highly repetitive sequences are interspersed throughout the intergenic regions
c. The genomes are extremely large, on the order of several billion base pairs
d. All of the above
e. None of the above

A

D. All of the above

49
Q

Synthesis of DNA by DNA polymerase III during replication requires a primer. The primer for initiation of synthesis at a replication origin is provided by a “primosome complex”. The relevant activity synthesizing the primer is

a. DNA polymerase I
b. DNA polymerase II
c. A special RNA polymerase
d. DNA helicase

A

A special RNA polymerase

50
Q

All of the following statements are true concerning DNA synthesis EXCEPT:

a. An RNA-DNA hybrid occurs at one stage
b. DNA is replicated by several DNA polymerases, one of which can synthesize DNA in a 5’ to 3’ direction and another of which synthesizes DNA in a 3’ to 5’ direction
c. The primer for DNA synthesis is RNA
d. DNA synthesis is discontinuous in the sense that small fragments of DNA are made first and then sealed together into long strands
e. DNA synthesis is semi-conservative, which means that daughter cells contain one complete parental DNA strand and one complete new DNA strand

A

DNA is replicated by several DNA polymerases, one of which can sythesize DNA in a 3’ to 5’ direction and another whichsyntheizes DNA in a 5’ to 3’ direction

51
Q

Which of the following are missing from a mature prokaryotic mRNA?

  1. Y/N 7-methylguanosine triphosphate (7-methyl-Gppp)
  2. Y/N 3’ poly-A tail
  3. Y/N 5’ untranslated sequences
A
  1. Yup
  2. Yup
  3. Nope
52
Q

DNA methylation in prokaryotes serves as a sort of primitive “immune recognition”. In eukaryotes, it doesn’t seem to serve this purpose, but methylation patterns can be heritable. What is this form of “inheritance” called?

A

Epigenetic inheritance

53
Q

Drawback associated with the use of some live, non-recombinant vaccines in current use can be broadly attributed to the following categories: (T/F)

  1. Residual virulence of the vaccine
  2. Presence of preservaites in the vaccine
  3. Lack of correct post-translational modification of proteins in the vaccine
  4. Contamination of th vaccine by other infectious agents
A
  1. Residual virulence of the vaccine- True
  2. Presence of preservaites in the vaccine - False
  3. Lack of correct post-translational modification of proteins in the vaccine- False
  4. Contamination of th vaccine by other infectious agents- True
54
Q

The genetic mechnism generating antigen fragment binding site diversity in the T-cell receptor genes most closely resembles that of:

a. the immunoglobulin genes
b. MHC class 1 antigen genes

C. MHC class 2 antigen genes

A

A. The immunoglobulin genes

55
Q

The antigenic diversity arising in retroviruses occurs primarily in the polypeptide prducts of which retroviral gene?

A. gag.

B. pol

C. env

D. none of the above

A

C. env

Molecular biology (Updated 2016) (15 decks)

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