Ch 8 Micro

DNA-mediated transformation

"naked" DNA is taken up from the environment by a bacterial cell

phenotype

An organism's observable physical characteristics.

replica plating

Technique for the simultaneous transfer of organisms in separated colonies from one medium to another.

carcinogens

chemicals that cause cancer; most are mutagens

Which of the following can be transferred from one cell to another by conjugation?

chromosomal DNA; plasmid DNA

haploid

contains a single set of genes

______ mutations are generally themes harmful to cells because they change all of the codons downstream of the mutation

frameshift

Which of the following terms describes the sequence of nucleotides (genetic makeup) of an organism or a cell?

genotype

An organism that does not require growth factors is called a(n)

prototroph

insertional inactivation

the gene into which a transposon jumps is inactivated by the event; the inserted DNA disrupts the function of the gene

"Jumping genes" or _____ can lead to changes in genotype within a cell or between cells.

transposons

A base substitution that results in a change in the amino acid encoded is called a(n) ______ mutation

missense

Mutation are rare because

most damage is repaired before it is passed on to progeny

Genetic change in bacteria occurs through which two mechanisms?

mutation; horizontal gene transfer

high copy number

occur in many copies in a cell

base substitution

occurs during DNA synthesis when an incorrect nucleotide is incorporated

Repair of nucleotide incorporation errors during the process of DNA replication is accomplished by _____ by DNA polymerase and by ____ repair

proofreading; mismatch

Mutation rates are low because proofreading and ___ mechanisms fix altered or damaged DNA before it can be passed to the progeny

repair

auxotroph

requires growth factors

Conjugation

DNA is transferred during cell-to-cell contact

Transduction

DNA is transferred from one bacterial cell to another by a bacteriophage

In humans, two of the gens associated with the development breast cancer encode enzymes involved in

DNA repair

Model system

E coli; cells grow quickly in small volumes of cheap media and accumulate in very large numbers

Which of the following mutations frequently results in the production of a shortened and non-functional protein because a different set of codons is translated?

Frameshift

narrow host range

can replicate in only one species

mutation

changes the existing nucleotide sequence of a cell's DNA which is then passed to the progeny through *vertical gene transfer*

frameshift mutation

changes the reading frame of the corresponding mRNA molecule so that an entirely different set of codons is translated

Cells that have the ability to take up DNA from the environment are called __ cells

competent

mismatch repair

fixes errors missed by the proofreading of DNA polymerase

The common consequence of a ______ mutation is the appearance of an early stop codon that produces a shortened and this non-functional protein

frameshift

spontaneous mutations

genetic changes that result from normal cell process; they occur randomly and genes. mutate spontaneously at infrequent but characteristic rates

natural selectin

selection by the environment of the best cells able to survive in that environment

DNA-mediated ____ involves the uptake of "naked" DNA by competent bacterial recipient cells

transformation

Conjugation, DNA-mediated ___ and _____ are methods of horizontal gene transfer in bacteria

transformation; transduction

Which of the following are methods of gene transfer in bacteria?

transformation; transduction; conjugation

Sequences of DNA that can move to new positions within the genome of a single cell are called

transposons

A point mutation involves any substitution of a single nucleotide

true

indirect selection

used to isolate an auxotrophic mutant from a prototrophic parent strain.

Ames test

uses histidine-requiring auxotroph of Salmonella typhimurium to measure the mutagenicity of a chemical

point mutation

when only one base pair is changed

missense mutation

when the altered codon codes for a different amino acid

If a scientist is working with bacteria that have the typical phenotype of those isolated from nature, the bacteria are considered to _____ type.

wild

Recognition and repair of errors in nucleotide incorporation by DNA polymerase is called

proofreading

Errors by DNA polymerase that incorporate the wrong nucleotide into replicating DNA can be repaired quickly by which two mechanisms?

proofreading by DNA polymerase; mismatch repair

Bacteria are a great model system for genetic studies because when they are grown to very high numbers in small volumes of simple media _________.

rare genetic changes that happen can be easily studied

_____ sometimes incorporates the incorrect nucleotide when generating a new strand of DNA during DNA _____; this leads to a detectable distortion in the DNA helix

DNa polymerase; replication

broad host range

can replicate in many different species

SOS repair

damaged DNA activates expression of several dozen genes that encode for the SOS system

genotype

sequence of nucleotides in the DNA

low copy number

occur in one or a few copies per cell

_______ are circular pieces of bacterial DNA that do not usually encode information essential to the life of a cell

plasmids

The return of a gene from a mutated state to its original, non-mutated state is called a

reversion

replicon

the DNA has an origin of replication; plasmids and chromosomes

The process in which better adapted organisms reproduce at higher rates in a given environment is called

natural selection

A base substitution that changes an amino acid-encoding codon to a stop codon is called a(n) ______ mutation

nonsense

SOS mutagenesis

SOS DNA polymerase has no proofreading ability and makes errors

horizontal gene transfer

the movement of DNA from one organism to another

Steps of DNA-mediated transformation

1. Double stranded DNA molecule binds to the surface receptor 2. Nucleases degrade one strand of double-stranded DNA at the cell surface 3. Single-stranded DNA enters the cell after one strand has been degraded 4. Single-stranded DNA integrates into genome after entering the cell 5. Strand being replaced by donor DNA is degraded

reversion (back mutation)

a mutation that changes back to its original and non-mutated state

competent

a specific physiological state that allows the cell to take up DNA

photoreactivation

an enzyme uses the energy of visible light o break the covalent bonds of the thymine dimer; restoring DNA to its original state

proofreading

dna polymerase checks the accuracy of their actions by removing a nucleotide the is not correctly hydrogen-bonded to the opposing nuclease

prototroph

does not require growth factors

homologous recombination

donor DNA becomes positioned next to the complementary region of the recipient cell's DNA; donor DNA then replaces a homologous segment of recipient DNA that is then degraded

excision repair

enzyme recognizes the major distortions in DNA that result from thymine dimer formation and removes the DNA strand with the damaged region

In bacterial conjugation, F+ donor cells are high frequency recombinant cells when the F plasmid

is integrated into the chromosome

transposons

jumping genes or pieces of DNA that can move from one location to another in a cell's genome (transposition)

In this image, the base substitution leading to cysteine is called a(n) ______ mutation

silent

Random genetic changes that occur as a result of natural cellular processes are called ______ mutations

spontaneous

synonymous mutation (silent mutation)

the change generates a codon that translates into the same amino acid as the original

knockout mutation

any mutation that totally inactivates the gene

Consider a population of bacteria susceptible to an antimicrobial, If a bacterium acquires a spontaneous mutation that gives resistance to the antimicrobial, this bacterium will ______ if the population is exposed to the antimicrobial.

grow without competition

In _____ gene transfer, DNA move from one organism to another, while in _________ gene transfer, DNA is passed from a parent cell to its progeny

horizontal; vertical

A point mutation always leads to a shift of the reading frame from the point of mutation downstream

false

direct selection

cells are inoculated onto an agar medium that supports the growth of the mutant and does not allow the parent to grow

A(n) ________ mutation results from an insertion or deletion of nucleotides, leading to a shift of the reading frame from the point of mutation downstream

frameshift

nonsense mutation

occurs when base substitution creates a stop codon that produces a shorter and non-functional protein

penicillin enrichment

selectively kills prototrophs and is sometimes used before replica plating to increase the proportion of auxotrophic mutants.