Week 8 Assignment MCB3020

By using a mutagen, the mutation rate can be increased to one mutant cell out of approximately Blank______ cells.

1,000 to 1,000,000

Although mismatch DNA repair and nucleotide excision repair address different types of lesions, they share three enzymes, Blank______, Blank______, and Blank______.

DNA polymerase I UvrD helicase DNA ligase

Which three statements regarding homologous recombination are correct?

It is the most common mechanism of DNA recombination. RecA protein is involved. Similar or identical DNA strands are broken and reunited.

Which statement regarding lethal mutations is false?

Lethal mutations are rare because most genes are not essential.

When DNA damage is so great that DNA synthesis stops, a control system called the _______ response occurs.

SOS

The structure used to establish physical contact between an F+ and F- cell is called a sex_____

pilus

Small, double-stranded DNA molecules that can exist independently of host chromosomes are called .

plasmids

Silent, missense, nonsense, and frameshift are all common types of_______ mutations.

point

The type of mutation that affects only a single base pair at a given DNA location is called a(n)__________ mutation.

point

A mutation can prevent a gene from being expressed, even if the coding sequence is completely unchanged.

true

Click and drag on elements in order Order these steps in simple transposition, with the first event at the top.

1. Transposase excises the mobile genetic element 2. Trasposase identifies a new insertion site and cleaves the stands 5 to 9 bases aprt 3. Transposase ligates the mobile genetic element DNA with the host insertion site 4. Host enzymes fill in gas, resulting in a 5 to 9 base duplication at either end of the mobile genetic element

Under normal growth conditions, the rate of naturally-occurring mutant cells is one mutant cell out of approximately Blank______ cells. Multiple choice question.

10^7 to 10^11

Alternative forms of a gene are called _____.

allele

R plasmids are best described as plasmids that Blank______.

carry genes that confer antibiotic resistance

The major mechanism by which bacteria and archaea evolve (acquire novel genes) is Blank______.

horizontal gene transfer

Which two of these missense mutations would be predicted to have the most severe effects on the function of the protein encoded by the mutated gene?

replacement of a nonpolar amino acid with a polar amino acid substitution of an amino acid located at the active site of an enzyme

An allele is most likely to persist in a population if it confers a survival advantage under Blank______ pressure.

selective

Point mutations that change the nucleotide sequence of a codon but do not change the amino acid encoded by that codon are called _________ mutations.

silent

The movement of a mobile genetic element is called _______.

transposition

The mismatch repair system of E. coli is able to detect mismatched bases because, for a short time, newly synthesized DNA strands are Blank______.

unmethlyated

In bacterial genetics, transformation is Blank______.

uptake of dNA from outside

This diagram illustrates binary fission, a type of_______ gene transfer commonly observed in bacteria and archaea.

vertical

Bacteriophages that lyse their host cells after completing one cycle of replication and assembly are called ________bacteriophages.

virulent or lytic

The most prevalent form of a gene, and its associated phenotype, is called the _________ type.

wild

Transposases are enzymes that recognize the ends of a(n) Blank______. Multiple choice question.

?

Which two of these bacterial mutants could be selected by exposing them to a particular stress condition and looking for growth?

A mutant resistant to a particular antibiotic A mutant resistant to bacteriophage infection

Which three types of mutations are classified as reversion mutations?

A second mutation creates a codon that replaces the wild type amino acid with a similar amino acid. A second mutation that restores the original wild-type sequence. A second mutation that creates a different codon that codes for the wild type amino acid.

Which three statements apply to an F' plasmid?

An F' plasmid is an erroneously excised plasmid. An F' plasmid has been excised from a bacterial chromosome. An F' plasmid includes some chromosomal genes.

Which three of these statements about nonsense mutations are correct?

By definition, they always produce stop codons. Effects range from mild to complete loss of normal gene function. They cause the early termination of translation.

Select three examples of chemical mutagens.

DNA-modifying agents intercalating agents base analogs

Which two statements correctly describe missense mutations?

Effects range from no change to complete loss of normal gene function. They are a single base substitution that changes a codon for one amino acid into a codon for a different amino acid

Which of these is the defining characteristic of an Hfr strain?

F plasmid integrated into the host chromosome

An F plasmid that has been excised from a bacterial chromosome, and includes some chromosomal genes, is called a(n) Blank______. Multiple choice question.

F' plasmid

Which two statements concerning horizontal gene transfer are correct?

Horizontal gene transfer helps microbes survive environmental stress. Horizontal gene transfer is common among microbes sharing a habitat.

A key component of the SOS response is the destruction of a transcriptional repressor protein called Blank______.

LexA

DNA segments that can repeatedly insert into one or more sites or into one or more genomes are called _________ _________elements.

MOBILE GENETIC

The general term for heritable changes in DNA sequence is_________

MUTATIONS

Mismatch repair Nucleotide excision repair Base excision repair

Mismatch repair: The strand lacking methylation is removed. Nucleotide excision repair: The strand with a DNA distortion is removed. Base excision repair: The strand with an apurinic or apyridinic site is removed.

MutSLH MutL-UvrD Single-stranded binding protein DNA polymerase I

MutSLH - Scan newly replicated DNA for mismatches MutL-UvrD - Separate the parental and new DNA strands around a mismatch Single-stranded binding protein - Protect the methylated (parental) DNA strand DNA polymerase I - Synthesize DNA complementary to the methylated (parental) strand

Match each type of excision repair with the type of lesion that it repairs. Nucleotide excision repair Base excision repair

Nucleotide Excision Repair: thymine dimer Base excision repair: apurinic or apyrimidinic site

Which approach would be used to screen for revertants from a lysine auxotroph?

Plate a large number of lysine auxotrophs on a minimal medium lacking lysine.

Which example of a missense mutation in a protein-encoding gene would most likely be a neutral mutation?

Replacement of a polar amino acid with another polar amino acid at the protein's surface

Which three of the following are correct descriptions of plasmids?

They are double-stranded DNA molecules. Some can integrate into host chromosomes. They can exist independently of host chomosomes

Which two of these descriptions apply to auxotrophs?

They are unable to grow on medium lacking a particular molecule, where the wild-type strain could grow. They have a conditional phenotype.

Which statement regarding viruses and their life cycles is false?

Viruses can replicate either within a host cell or autonomously.

Which of the following statements about viruses and transduction is false?

Viruses escaping a bacterium can find a new host cell and move genes to an archaeon

Some instances of antibiotic resistance occur by spontaneous chromosomal mutation. In these cases, the mutation results in Blank______.

a change in the drug target such that the drug can no longer bind

A suppressor mutation, which returns a mutant back to its wild-type phenotype, occurs at Blank______ the first mutation.

a different site from

A genetic selection differs from a genetic screen in that Blank______.

a genetic selection adjusts the environment so that only mutants of the desired phenotype can grow

Select two examples of mutations that affect regulatory sequences of microbial genes.

a mutation in a promoter so that RNA polymerase cannot bind a mutation in the lac operator so the lac repressor cannot bind

Vertical gene transfer is observed in Blank______.

all organisms

An organism with a mutation that affects its ability to synthesize a biochemical essential for its growth is known as a(n) _________.

auxotrophs

In bacteria, conjugation refers to the transfer of DNA by Blank______.

cell-to-cell contact

Base analogues, DNA-modifying agents, and intercalating agents are three types of ________ mutagens.

chemical

Mutations that are expressed only under certain environmental conditions are called _____ mutations.

conditional

Antibiotic resistance genes like those found on R plasmids often code for enzymes that Blank______.

destroy or modify antibiotics

Which two of the following are types of DNA damage that are corrected by nucleotide excision repair?

distortions in the double helix thymine dimers

In mismatch repair, the DNA strand to be removed is targeted because it Blank______.

does not have the parental methylation pattern

DNA proofreading occurs Blank______.

during DNA replication, before the next nucleotide is added

Transduction, the horizontal transfer of genes by virus particles, occurs through Blank______. Multiple choice question.

errors in the virus life cycle

In simple transposition, a mobile genetic element Blank______.

excises from one location and inserts in a different location in the same genome

Which type of DNA repair corrects damage (e.g., thymine dimers) that causes distortions in the DNA double helix? Multiple choice question.

excision repair

Fill in the blank question. William Hayes' 1952 experiments demonstrated that conjugation is unidirectional and identified strains he named F+ and F-. The "F" stands for .

fertile or fertility

A mutation that leads to a change from wild type to a mutant form is called a(n) __________ mutation.

forward

The major conclusion of Hayes' 1952 experiments, which demonstrated the existence of F+ and F- strains, was that Blank______.

gene transfer by conjugation is unidirectional

Hfr strains of bacteria are so named because they undergo a ________(high/low) frequency of ______.

high / recombination, recombinants, recombinates

The most common type of DNA recombination (e.g., during meiosis or bacterial horizontal gene transfer) is ________recombination between similar or identical DNA strands.

homologous

Mechanisms that result in the transfer of genes from one independent, mature organism to another are collectively called _________ gene transfer.

horizontal

Mechanisms that result in the transfer of genes from one independent, mature organism to another are collectively called _______ gene transfer.

horizontal, lateral, HGT

In a genetic selection, the wild type organisms are Blank______, whereas in a genetic screen, the wild type organisms are Blank______.

killed / alive

A bacterium that has been infected by a temperate bacteriophage, and is therefore carrying a prophage, is known as a(n)

lysogen

Point mutations in a single base that result in a change to the amino acid encoded are called __________mutations.

missense

Select three synonyms for genetic elements that can move around genomes by transposition.

mobile genetic elements jumping genes transposable elements

Possible causes of spontaneous mutation include Blank______. [Choose 3.]

mobile genetic elements spontaneous lesions in DNA errors in DNA replication

Transition mutations, which result in purine for purine substitution or pyrimidine for pyrimidine substitution, are Blank______ common than transversion mutations.

more

Silent mutations have no change in phenotype because Blank______.

more than one codon exists for most amino acids

The T4 phage of E. coli is a virulent bacteriophage, meaning that it Blank______.

multiplies in and lyses its host after infection

A missense mutation that has little to no effect on the activity of a gene product is called a(n) mutation.

neutral

A tautomeric form is an isomer of a nucleotide in which the Blank______ is changed.

nitrogenous base

Fill in the blank question. The ability of DNA polymerase to detect and correct errors before the next nucleotide is added is called_______

proofreading

The genome of a temperate bacteriophage that has been inserted into a bacterial genome is called a(n)_______

prophage

A wild-type chemoorganotroph like E. coli able to grow on a minimal medium containing only salts and a carbon source is known as a(n) ___________ . These wild-type strains may give rise to mutants incapable of survival without additional nutrients, like a particular amino acid.

prototroph

A mutant that can survive exposure to some pathogen, chemical, or antibiotic, is a(n) _______ mutant.

resistant

Select the best definition of mobile genetic elements.

specific DNA segments that can repeatedly insert into one or more sites or into one or more genomes

Mutations that result from head-on collisions between the replisome and RNA polymerase are considered to be Blank______ mutations.

spontaneous

Some instances of antibiotic resistance result in modification of the antibiotic target such that it is no longer inhibited by the antibiotic. Such events generally result from Blank______.

spontaneous chromosomal mutations

A second mutation that occurs at a different site from the first mutation, and which returns the mutant back to the wild-type phenotype, is a(n) mutation.

suppresor

Spontaneous mutations can occur when a nitrogenous base shifts to a different isomer, also called a(n) Blank______. Multiple choice question.

tautomeric form

A bacteriophage that can insert its genome into a bacterial chromosome is known as a(n) ______bacteriophage.

temperate or lysogenic

Mismatched DNA bases in the double helix are repaired by Blank______.

the mismatch repair system that eliminates the daughter strand and re-synthesizes it on the parental strand template

Which phrase best describes the form of a gene designated the "wild type?"

the more prevalent form of the gene

When the mismatch repair system of E. coli detects mismatched bases, it is able to determine the strand that needs repair, because Blank______ is methylated.

the old strand

Errors made during the packaging of bacteriophage genes into capsids may result in the transfer of bacterial genes, a mechanism of horizontal gene transfer known as Blank______.

transduction

Fill in the blank question. The process of taking up DNA from the surroundings, and maintenance of the DNA in a heritable form, is called .

transformation

Nucleotide substitutions that result in purine for purine or pyrimidine for pyrimidine mutations are known as ________ mutations.

transition

Which enzyme is encoded in insertion sequences, recognizes inverted repeats, and cuts DNA to remove a mobile genetic element?

transposase