Microbiology Ch 8

Plasmid

A small extrachromosomal DNA molecule that replicates independently of the chromosome and generally encodes information not essential to the life of the cell.

Which of the following statements about R plasmids is FALSE?

R plasmids are usually narrow host range plasmids.

If the DNA is heavily damaged, what repair mechanism will the cell likely use?

SOS repair

Genomic island

Large segment of DNA that has been acquired from another species through horizontal gene transfer.

Transduction

Mechanism of horizontal gene transfer between bacteria in which bacterial DNA is transferred inside a phage coat.

Conjugation

Mechanism of horizontal gene transfer in which the donor cell must physically contact the recipient cell

A researcher discovered a mutation in bacteria that causes rapid degradation of the bacterial DNA. Which of the following provides the best explanation of the mutation?

Methylation of the bacterial DNA was decreased by the mutation.

Which of the following statements about a mutation is FALSE?

Mutations are passed on to a cell's progeny. B) All mutations lead to changes in the phenotype of the cell. All mutations lead to changes in the genotype of the cell. Mutations can occur spontaneously. All of these choices are correct.

Which of the following is true about phenotype?

Phenotype is the expression of the genotype.

Which of the following is true about phenotype?

Phenotype the expression of the genotype.

Homologous recombination

genetic exchange between stretches of similar or identical nucleotide sequences. Involves a type of breakage and rejoining of DNA into new combinations and replacement of DNA

Non-homologous recombination

genetic recombination that does not require the two DNAs to have similar sequences in the region of recombination. Frequently the process involves addition and not replacement of genes

Oxidized guanine can result in base substitutions. Which enzyme would remove an oxidized nucleobase from a sugar-phosphate backbone to fix the problem?

glycosylase

A mutation in a gene that results in a product that is only partially functional is called a

missense mutation.

Every 24 hours, the DNA in every cell in the human body is spontaneously damaged

more than 10,000 times.

Any change in the nucleotide sequence of a gene is called a

mutation

The reason why penicillin-resistant cells will take over a population if the cells are grown in the presence of penicillin is

natural selection.

Which of the following mutagens is considered an alkylating agent?

nitrous acid

What percentage of S. aureus strains from hospital patients were resistant to methicillin in 2004?

over 60%

Mutation

A change in the nucleotide sequence of a cell's DNA, which is then passed on to daughter cells. A mutation can alter the protein which it encodes.

Prototroph

A microorganism that has no requirements for organic growth factors because it can synthesize them.

Replicon

A piece of DNA that has an origin of replication and is therefore capable of replicating.

Which of the following statements about conjugation is FALSE?

Conjugation requires contact between donor and recipient cells. The sex pili of donor cells bind to specific sites on recipient cells. A single strand of the F plasmid enters the recipient cell. The transfer of DNA only takes a few minutes. E) All of these choices are correct.

Haploid

Containing only a single set of genes

Extrachromosomal

DNA that is not part of a chromosome

Fragments of chromosomal DNA, full chromosomes of DNA, and plasmids are replicons.

False

Genomic islands are large RNA segments in the cell's genome that originate in other species.

False

Transposable element (Transposon)

Genes that move from one replicon to another site on the same replicton or to another replicon in the same cell. Involves non homologous recombination.

Phenotype

The observed characteristics of a cell resulting from the expression of the genotype.

Genotype

The sequence of nucleotides in the DNA of an organism

A researcher noted in a bacterial species that there were more mutations in stretches of DNA having higher proportions of thymine than the other nucleotides. Which is the most probable explanation for this observation?

Thymine dimers are more likely to form in those stretches.

Reactive oxygen

Toxic forms of oxygen that can modify and damage DNA.

Which of the following statements about transformation is FALSE?

Transformation requires involves the uptake of "naked" DNA. The recipient must be competent. Double-stranded DNA binds to the surface of recipient cells. D) Double-stranded DNA enters the recipient cell. All of these are false.

Horizontal gene transfer

Transmission of DNA from one bacterium to another through conjugation , DNA mediated transformation, or tranduction. Also called lateral gene transfer.

Homologous recombination can happen only if the donor DNA is similar in nucleotide sequence to a region in the recipient cell's genome.

True

Mismatch repair fixes errors missed by DNA polymerase.

True

Most plasmids are double-stranded DNA molecules.

True

Replica plating is useful in isolating auxotrophic mutants.

True

Auxotroph

a microorganism that requires an organic growth factor

A bacterial cell that requires a growth factor to grow is called

an auxotroph.

Which one of the following mutagens causes frameshift mutations?

ethidium bromide

Oxygen radicals can damage cells by

inducing point mutations.

DNA mediated transformation

mechanism of horizontal gene transfer between bacteria in which the bacterial DNA is transferred as "naked" DNA

The transfer of bacterial DNA by a virus is called

transduction

The transfer of bacterial DNA by a virus is called

transduction.

Barbara McClintock won the Nobel Prize for her discovery of

transposons

Which one of the following mutagens causes the formation of thymine dimers?

ultraviolet light