Week 8 Assignment

Which two types of mutations are classified as reversion mutations? - A second mutation that creates a new codon that codes for the same amino acid. - A mutation that causes the wild type strain to become a mutant strain. - A second mutation that restores the original wild-type sequence. - A second frameshift mutation that restores an original reading frame.

- A second mutation that creates a new codon that codes for the same amino acid - A second mutation that restores the original wild-type sequence

Which three of the following descriptions apply to an F' plasmid? - A cell carrying an F' plasmid is always considered an Hfr cell. - It includes some chromosomal genes. - It has been excised from a bacterial chromosome. - it is an erroneously excised plasmid. - It is smaller than a normal F plasmid.

- It includes some chromosomal genes - It has been excised from a bacterial chromosome - it is an erroneously excised plasmid

Which three of the following statements are correct regarding conjugation in Gram-positive bacteria such as Enterococcus faecalis. - Peptides are released to activate transfer genes. - The donor cell typically dies following gene transfer. - The proteins involved are not related to those in Gram-negatives. - A sex pilus may not be required. - Donor and recipient cells adhere directly to each other.

- Peptides are released to activate transfer genes - A sex pilus may not be required - Donor and recipient cells adhere directly to each other

Which three of the following statements regarding homologous recombination are correct? - Similar or identical DNA strands are broken and reunited. - It is the most common mechanism of DNA recombination. - Recombinases recognize specific DNA sequences. - It occurs only during meiosis. RecA protein is involved.

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

Which two of these descriptions apply to auxotrophs? - They are resistance mutants. - They are unable to grow on medium lacking a particular molecule, where the wild-type strain could grow. - They are chemoorganotrophs able to grow on a minimal medium containing only salts and a carbon source. - They have a conditional phenotype.

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

Which three of these statements are correct about nonsense mutations? - They involve a single base substitution that changes a codon for one amino acid to a codon for a different amino acid. - They are typically not as severe when they occur near the beginning of a gene. - They cause the early termination of translation. - Effects range from mild to complete loss of normal gene function. - By definition, they always produce stop codons.

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

Which two statements correctly describe missense mutations? - They involve a single base substitution that changes a codon for one amino acid into another. - Effects range from no change to complete loss of normal gene function. - They are typically not as severe when they occur near the end of a gene. - They cause the early termination of translation. - By definition, they always produce stop codons.

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

Which two of these statements are correct about frameshift mutations? - By definition, they always produce stop codons. - They are typically not as severe when they occur near the beginning of a gene. - They usually yield mutant phenotypes. - They involve a single base substitution that changes a codon for one amino acid into another. - They usually result in the synthesis of nonfunctional proteins.

- They usually yield mutant phenotypes - They usually result in the synthesis of nonfunctional proteins

Select two examples of mutations that affect regulatory sequences of microbial genes. - a mutation that affects the active site of β-galactosidase - a mutation in a ribosomal RNA gene that alters the structure of 30S ribosomes - a mutation in a promoter so that RNA polymerase cannot bind - a mutation in the lac operator so the lac repressor cannot bind - a mutation that affects the ability of transfer RNA to bind to a particular amino acid

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

A resistance mutant may have acquired resistance to which three of the following? - antibiotic - pathogen - transformation - nutrient deficiency - chemical

- antibiotic - pathogen - chemical

Which two of these features are common to all transposable elements? inverted repeats - reverse transcriptase - gene for a recombinase (e.g., transposase) - gene for antibiotic resistance - gene for resolvase

- inverted repeats - gene for a recombinase (e.g., transposase)

Which three of these factors contribute to the extreme radiation resistance of Deinococcus radiodurans? - several unique DNA repair mechanisms - proteins that quickly repair damage to genome - two homologous chromosomes - radiation-resistant proteins - thick cell wall blocks radiation - complex, atypical electron transport chain

- proteins that quickly repair damage to genome - two homologous chromosomes - radiation-resistant proteins

Which two of these missense mutations would be likely to have a significant effect on the function of the protein encoded by the mutated gene? - substitution of an amino acid located at the active site of an enzyme - replacement of an amino acid located in a surface loop of an enzyme - replacement of a hydrophobic amino acid with a different hydrophobic amino acid - replacement of a nonpolar amino acid with a polar amino acid

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

Which of these types of DNA damage are usually mended by direct DNA repair? thymine dimers gaps in DNA alkylated bases distortions in the double helix

- thymine dimers - alkylated bases

Select three synonyms for genetic elements that can move around genomes by transposition. - site-specific plasmids - transposable elements - jumping genes - mobile genetic elements - introns

- transposable elements - jumping genes - mobile genetic elements

By using mutagens, the mutation rate can be increased to one mutant cell out of approximately how many cells?

1,000-1 mil

Under normal conditions, the rate of naturally occurring mutant cells is one mutant cell out of approximately how many cells?

10^7 to 10^11

In bacteria, an insertion sequence (or IS element) is typically about what size?

750-1600 base pairs

Select the best definition of transposable elements. a) short segments of DNA flanked by inverted repeats, that contain only the gene for transposase b) specific DNA segments that can repeatedly insert into one or more sites or into one or more genomes c) small DNA molecules within a cell that are physically separated from a chromosomal DNA and can replicate independently d) bacteriophages that contain both phage and bacterial DNA, usually the result of lysogenization

B

Vertical gene transfer can be best defined as the transfer of genes _____. a) between any two individuals of different species b) from parents to progeny c) between any two individuals of the same species d) from progeny to parents

B

Which example of a missense mutation in a protein-encoding gene would most likely be a neutral mutation? a) Replacement of a polar amino acid with a nonpolar amino acid at the protein's outer surface b) Replacement of a polar amino acid with another polar amino acid at the protein's surface c) Replacement of a polar amino acid with another polar amino acid in the protein's interior d) Replacement of a polar amino acid with a nonpolar amino acid in the protein's interior

B

Which scientist discovered mobile genetic elements?

Barbara McClintock

The easiest and most straightforward example of screening for a mutant phenotype would be which of these? a) Detecting a bacterium that is resistant to bacteriophage infection b) Detecting a histidine auxotroph c) Detecting an albino mutant when the wild type is blue d) Detecting a bacterium that has a mutated tRNA molecule

C

Select the best definition of horizontal gene transfer. a) persistence of a gene that confers a survival advantage b) transfer of genes from parents to progeny c) DNA transfer between animals that move on land d) transfer of genes from one independent, mature organism to another

D

When does DNA proofreading occur? a) only after errors in transcription are detected b) after DNA replication is completed, and mismatched nucleotides are detected c) before DNA replication begins, to make sure all nucleotides are correctly matched d) during DNA replication, before the next nucleotide is added

D

Which of the following statements about viruses and transduction is false? a) All cellular organisms are susceptible to viral infections. b) Transduction is a natural consequence of the viral life cycle and requires no special host cell structures. c) Viruses can move genes from one bacterium to another in natural environments. d) Viruses escaping a bacterium can move genes to an archaeon when they find a new host cell.

D

Which of these descriptions applies to prototrophs? a) They have a conditional phenotype. b) They are unable to grow on medium lacking a particular molecule, where the wild-type strain could grow. c) They are able to use light as an energy source. d) They are chemoorganotrophs able to grow on a minimal medium containing only salts and a carbon source.

D

Which of these is the defining characteristic of an Hfr strain? a) Multiple sex pili b) Very efficient DNA replication c) F plasmid in their cytoplasm c) F plasmid integrated into the host chromosome

D

connects the newly synthesized DNA with the old DNA

DNA ligase

replaces nucleotides that were excised

DNA polymerase

three examples of chemical mutagens.

DNA-modyfing agents intercalating agents base analogs

An F plasmid that has been excised from a bacterial chromosome, and which therefore also includes some chromosomal genes, is called a(n) _____.

F' plasmid

True or false: Conjugation occurs only in Gram-negative bacteria.

False

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

LexA

removes DNA around a mismatch

MutH

scans newly replicated DNA for mismatches

MutS

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

SOS

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

a different site from

Alternative forms of a gene are called _________

allele

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

auxotroph

mutant cannot synthesize an essential molecule such as an amino acid

auxotroph

There are two types of excision repair systems that correct damage that causes distortions in the DNA double helix: __________ excision repair and _________ excision repair.

base nucleotide

A chemical agent that causes cancer is specifically called a(n) __________

carcinogen

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

cell-to-cell contact

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

chemical

A bacterial cell that is able to take up DNA and be transformed is said to be __________

competent

A mutant strain of E. coli that grows normally at 30°C, but dies at 40°C, is a(n)_________ mutant.

conditional

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

conditional

phenotype is only affected at high temperatures

conditional

Thymine dimers can be corrected by photoreactivation, which is a type of ___________ DNA repair.

direct

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

excision repair

True or false: The Ames test can determine whether a particular substance is carcinogenic.

false

William Hayes' 1952 experiments demonstrated that conjugation is unidirectional and identified strains he named F+ and F-. The "F" stands for ___________

fertile

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

forward

Mutations that arise from the insertion or deletion of base pairs within the coding region of a gene are specifically called __________ mutations.

frameshift

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

gene transfer by conjugation is unidirectional

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

high recombination

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

Transposases are enzymes that recognize the ends of a(n) _______.

insertion

Mobile genetic elements were discovered by Barbara McClintock in the 1940s, during her studies of what organism?

maize

Point mutations that involve a single base substitution and result in a change to the amino acid encoded are called __________ mutations. These mutations may or may not have a significant impact on the protein structure.

missense

A point mutation that involves a single base substitution and results in a change to the amino acid encoded by that codon is specifically called a _____.

missense mutation

Transition mutations, which result in substitution of the alternate purine for the original purine, or the alternate pyrimidine for the original pyrimidine, are __________ common than transversion mutations.

more

mutation affects the appearance of colonies

morphological

The general term for heritable changes in DNA sequence is ___________

mutations

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 _____ is changed.

nitrogenous base

Point mutations that result in a new stop codon are called _________ mutations.

nonsense

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

The ability of DNA polymerase to detect and correct errors before the next nucleotide is added is called ___________

proofreading

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

prototroph

Damage to DNA in which both bases of a pair are missing or damaged, or where there is a gap opposite a lesion, is usually repaired by a process called __________ repair.

recombination/excision/recombinational

The bacterium Deinococcus radiodurans is best known for its ability to ________.

resist damage by radiation

mutant is not affected by a particular pathogen or chemical

resistance

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

resistant

The use of a detection system to locate a microbe with a particular mutant phenotype is generally known as ____.

screening

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

A mutation that caused the codon CGU to change to CGC, which does not affect the amino acid encoded, could be described by which two of these terms?

silent point

Mutations that result from the activity of mobile genetic elements called transposons are considered to be which type of mutations?

spontaneous

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

suppressor

If a bacterial cell is competent, that means it can _____.

take up DNA and become transformed

Spontaneous mutations can occur when a nitrogenous base shifts to a different isomer, also called a(n) ____.

tautomeric form

In bacterial genetics, transformation is _____.

the uptake of DNA by a bacterial cell

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

DNA segments that can repeatedly insert into one or more sites or into one or more genomes are called ___________ elements.

transposable

An insertion sequence or IS element consists only of a pair of inverted repeats surrounding a gene coding for the enzyme _____.

transposase

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

transposase

The movement of a mobile genetic element is called _________

transposition

The movement of a mobile genetic element is called _____________

transposition

Possible causes of spontaneous mutation include

transposons spontaneous lesions in DNA errors in DNA replication

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

true

True or false: Lethal mutants can be recovered only if they are conditional mutants.

true

True or false: Most transposable elements contain a transposase gene and inverted repeats.

true

Another term for the transfer of genes from parents to progeny is ___________ gene transfer

vertical

Bacteriophages that lyse their host cells soon after infection are called ___________ bacteriophages.

virulent/lytic

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

wild type