Microbiology for Allied Health Students

Molly Smith, Sara Selby

Chapter 18

Mechanisms of Microbial Genetics - all with Video Answers

Educators

AG

Chapter Questions

Problem 1

DNA does all but which of the following?
a. serves as the genetic material passed from parent to offspring
b. remains constant despite changes in environmental conditions
c. provides the instructions for the synthesis of messenger RNA
d. is read by ribosomes during the process of translation

Dennis Howard

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Problem 2

According to the central dogma, which of the following represents the flow of genetic information in cells?
a. protein to DNA to RNA
b. DNA to RNA to protein
c. RNA to DNA to protein
d. DNA to protein to RNA

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Problem 3

Which of the following is the enzyme that replaces the RNA nucleotides in a primer with DNA nucleotides?
a. DNA polymerase III
b. DNA polymerase I
c. primase
d. helicase

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Problem 4

Which of the following is not involved in the initiation of replication?
a. ligase
b. DNA gyrase
c. single-stranded binding protein
d. primase

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Problem 5

Which of the following enzymes involved in DNA replication is unique to eukaryotes?
a. helicase
b. DNA polymerase
c. ligase
d. telomerase

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Problem 6

Which of the following would be synthesized using $5^{\prime}$ -CAGTTCGGA-3' as a template?
a. $3^{\prime}-$ AGGCTTGAC-4'
b. $3^{\prime}-$ TCCGAACTG-5'
c. $3^{\prime}$ -GTCAAGCCT-5'
d. $3^{\prime}-$ CAGTTCGGA-5'

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Problem 7

During which stage of bacterial transcription is the $\sigma$ subunit of the RNA polymerase involved?
a. initiation
b. elongation
c. termination
d. splicing

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Problem 8

Which of the following components is involved in the initiation of transcription?
a. primer
b. origin
c. promoter
d. start codon

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Problem 9

Which of the following is not a function of the 5 ' cap and 3' poly-A tail of a mature eukaryotic mRNA molecule?
a. to facilitate splicing
b. to prevent mRNA degradation
c. to aid export of the mature transcript to the cytoplasm
d. to aid ribosome binding to the transcript

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Problem 10

Mature mRNA from a eukaryote would contain each of these features except which of the following?
a. exon-encoded RNA
b. intron-encoded RNA
c. 5' cap
d. 3 ' poly-A tail

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Problem 11

Which of the following is the name of the threebase sequence in the mRNA that binds to a tRNA molecule?
a. $\mathrm{P}$ site
b. codon
c. anticodon
d. CCA binding site

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Problem 12

Which component is the last to join the initiation complex during the initiation of translation?
a. the mRNA molecule
b. the small ribosomal subunit
c. the large ribosomal subunit
d. the initiator tRNA

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Problem 13

During elongation in translation, to which ribosomal site does an incoming charged tRNA molecule bind?
a. A site
b. $\mathrm{P}$ site
c. $\mathrm{E}$ site
d. $\mathrm{B}$ site

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Problem 14

Which of the following is the amino acid that appears at the $\mathrm{N}$ -terminus of all newly translated prokaryotic and eukaryotic polypeptides?
a. tryptophan
b. methionine
c. selenocysteine
d. glycine

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Problem 15

When the ribosome reaches a nonsense codon, which of the following occurs?
a. a methionine is incorporated
b. the polypeptide is released
c. a peptide bond forms
d. the A site binds to a charged tRNA

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Problem 16

Which of the following is a change in the sequence that leads to formation of a stop codon?
a. missense mutation
b. nonsense mutation
c. silent mutation
d. deletion mutation

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Problem 17

The formation of pyrimidine dimers results from which of the following?
a. spontaneous errors by DNA polymerase
b. exposure to gamma radiation
c. exposure to ultraviolet radiation
d. exposure to intercalating agents

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Problem 18

Which of the following is an example of a frameshift mutation?
a. a deletion of a codon
b. missense mutation
c. silent mutation
d. deletion of one nucleotide

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Problem 19

Which of the following is the type of DNA repair in which thymine dimers are directly broken down by the enzyme photolyase?
a. direct repair
b. nucleotide excision repair
c. mismatch repair
d. proofreading

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Problem 20

Which of the following regarding the Ames test is true?
a. It is used to identify newly formed auxotrophic mutants.
b. It is used to identify mutants with restored biosynthetic activity.
c. It is used to identify spontaneous mutants.
d. It is used to identify mutants lacking photoreactivation activity.

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Problem 21

Which is the mechanism by which improper excision of a prophage from a bacterial chromosome results in packaging of bacterial genes near the integration site into a phage head?
a. conjugation
b. generalized transduction
c. specialized transduction
d. transformation

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Problem 22

Which of the following refers to the uptake of naked DNA from the surrounding environment?
a. Conjugation
b. generalized transduction
c. specialized transduction
d. transformation

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Problem 23

The F plasmid is involved in which of the following processes?
a. Conjugation
b. transduction
c. transposition
d. transformation

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Problem 24

Which of the following refers to the mechanism of horizontal gene transfer naturally responsible for the spread of antibiotic resistance genes within a bacterial population?
a. Conjugation
b. generalized transduction
c. specialized transduction
d. transformation

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Problem 25

An operon of genes encoding enzymes in a biosynthetic pathway is likely to be which of the following?
a. inducible
b. repressible
c. constitutive
d. monocistronic

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Problem 26

An operon encoding genes that are transcribed and translated continuously to provide the cell with constant intermediate levels of the protein products is said to be which of the following?
a. repressible
b. inducible
c. constitutive
d. activated

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Problem 27

Which of the following conditions leads to maximal expression of the lac operon?
a. lactose present, glucose absent
b. lactose present, glucose present
c. lactose absent, glucose absent
d. lactose absent, glucose present

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Problem 28

Which of the following is a type of regulation of gene expression unique to eukaryotes?
a. attenuation
b. use of alternate $\sigma$ factor
c. chemical modification of histones
d. alarmones

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Problem 29

True/False
Cells are always producing proteins from every gene they possess.

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Problem 30

True/False
More primers are used in lagging strand synthesis than in leading strand synthesis.

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Problem 31

True/False
Each codon within the genetic code encodes a different amino acid.

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Problem 32

True/False
Carcinogens are typically mutagenic.

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Problem 33

True/False
Asexually reproducing organisms lack mechanisms for generating genetic diversity within a population.

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Problem 34

The process of making an RNA copy of a gene is called _____ .

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Problem 35

A cell's $\quad$ remains constant whereas its phenotype changes in response to environmental influences.

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Problem 36

The enzyme responsible for relaxing supercoiled DNA to allow for the initiation of replication is called _____ .

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Problem 37

Unidirectional replication of a circular DNA molecule like a plasmid that involves nicking one DNA strand and displacing it while synthesizing a new strand is called _____ .

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Problem 38

A _______ mRNA is one that codes for multiple polypeptides.

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Problem 39

The protein complex responsible for removing intron-encoded RNA sequences from primary transcripts in eukaryotes is called the ______ .

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Problem 40

The third position within a codon, in which changes often result in the incorporation of the same amino acid into the growing polypeptide, is called the ______ .

Joanna Quigley

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Problem 41

The enzyme that adds an amino acid to a tRNA molecule is called _____ .

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Problem 42

A chemical mutagen that is structurally similar to a nucleotide but has different base-pairing rules is called a _____ .

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Problem 43

The enzyme used in light repair to split thymine dimers is called ____ .

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Problem 44

The phenotype of an organism that is most commonly observed in nature is called the _____ .

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Problem 45

A small DNA molecule that has the ability to independently excise from one location in a larger DNA molecule and integrate into the DNA elsewhere is called a ____ .

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Problem 46

_____ is a group of mechanisms that allow for the introduction of genetic material from one organism to another organism within the same generation.

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Problem 47

The DNA sequence, to which repressors may bind, that lies between the promoter and the first structural gene is called the _____ .

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Problem 48

The prevention of expression of operons encoding substrate use pathways for substrates other than glucose when glucose is present is called ______ .

Joanna Quigley

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Problem 49

Can two observably different cells have the same genotype? Explain.

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Problem 50

Why is primase required for DNA replication?

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Problem 51

What is the role of single-stranded binding protein in DNA replication?

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Problem 52

Below is a DNA sequence. Envision that this is a section of a DNA molecule that has separated in preparation for replication, so you are only seeing one DNA strand. Construct the complementary DNA sequence (indicating 5' and 3 ' ends).

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Problem 53

What is the purpose of RNA processing in eukaryotes? Why don't prokaryotes require similar processing?

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Problem 54

Below is a DNA sequence. Envision that this is a section of a DNA molecule that has separated in preparation for transcription, so you are only seeing the antisense strand. Construct the mRNA sequence transcribed from this template.
Antisense DNA strand: 3 '-T A C T G A C T G A C G A T C-5'

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Problem 55

Why does translation terminate when the ribosome reaches a stop codon? What happens?

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Problem 56

How does the process of translation differ between prokaryotes and eukaryotes?

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Problem 57

What is meant by the genetic code being nearly universal?

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Problem 58

Below is an antisense DNA sequence. Translate the mRNA molecule synthesized using the genetic code, recording the resulting amino acid sequence, indicating the $\mathrm{N}$ and $\mathrm{C}$ termini.
Antisense DNA strand: 3'-T A C T G A C T G A C G A T C-5'

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Problem 59

Why is it more likely that insertions or deletions will be more detrimental to a cell than point mutations?

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Problem 60

Briefly describe two ways in which chromosomal DNA from a donor cell may be transferred to a recipient cell during the process of conjugation.

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Problem 61

Describe what happens when a nonsense mutation is introduced into the gene encoding transposase within a transposon.

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Problem 62

What are two ways that bacteria can influence the transcription of multiple different operons simultaneously in response to a particular environmental condition?

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Problem 63

A pure culture of an unknown bacterium was streaked onto plates of a variety of media. You notice that the colony morphology is strikingly different on plates of minimal media with glucose compared to that seen on trypticase soy agar plates. How can you explain these differences in colony morphology?

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Problem 64

Review Figure 11.4 and Figure $11.5 .$ Why was it important that Meselson and Stahl continue their experiment to at least two rounds of replication after isotopic labeling of the starting DNA with ${ }^{15} \mathrm{~N}$, instead of stopping the experiment after only one round of replication?

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Problem 65

If deoxyribonucleotides that lack the 3 '-OH groups are added during the replication process, what do you expect will occur?

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Problem 66

Predict the effect of an alteration in the sequence of nucleotides in the -35 region of a bacterial promoter.

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Problem 67

Label the following in the figure: ribosomal E, P, and A sites; mRNA; codons; anticodons; growing polypeptide; incoming amino acid; direction of translocation; small ribosomal unit; large ribosomal unit.

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Problem 68

Prior to the elucidation of the genetic code, prominent scientists, including Francis Crick, had predicted that each mRNA codon, coding for one of the 20 amino acids, needed to be at least three nucleotides long. Why is it not possible for codons to be any shorter?

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Problem 69

Below are several DNA sequences that are mutated compared with the wild-type sequence: 3'-T A C T G A C $T$ G A C G A T C-5'. Envision that each is a section of a DNA molecule that has separated in preparation for transcription, so you are only seeing the template strand. Construct the complementary DNA sequences (indicating 5' and 3 ' ends) for each mutated DNA sequence, then transcribe (indicating 5' and 3 ' ends) the template strands, and translate the mRNA molecules using the genetic code, recording the resulting amino acid sequence (indicating the $\mathrm{N}$ and $\mathrm{C}$ termini). What type of mutation is each?

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Problem 70

Why do you think the Ames test is preferable to the use of animal models to screen chemical compounds for mutagenicity?

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Problem 71

The following figure is from Monod's original work on diauxic growth showing the growth of $E$. coli in the simultaneous presence of xylose and glucose as the only carbon sources. Explain what is happening at points A-D with respect to the carbon source being used for growth, and explain whether the xylose-use operon is being expressed (and why). Note that expression of the enzymes required for xylose use is regulated in a manner similar to the expression of the enzymes required for lactose use.

Dennis Howard

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