Lecture 10. Chapter 8

An auxotroph can be isolated from a prototrophic parent strain by ___ selection.

indirect

___ is used to fix nucleotide incorporation errors by proofreading function of DNA polymerase.

mismatch repair (213)

What are possible outcomes of a base substitution?

missense mutation, silent mutation, nonsense mutation

A ___ is an agent that induces changes in DNA.

mutagen (not mutation: mutation is a change in the DNA. The agent that causes the change is a mutagen.)

Chemical mutagens that modify ___ increase the odds of incorrect nucleotide incorporation during DNA replication.

nucleobases

Which type of DNA repair is shown in this figure?

photoreactivation

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

proofreading (213)

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

repair (213)

True or false: a point mutation always leads to a shift of the reading frame from the point of mutation downstream.

False (ex: silent mutation)

What mutations frequently results in the production of a shortened and nonfunctional protein because a different set of codons is translated?

Frameshift (p. 209)

Replica plating is a form of ___ selection in which duplicate patterns of colonies are plated onto nutrient agar and a plate with glucose-salts agar.

Indirect (215-216)

___ mutations are genetic changes caused by factors from outside the cell such as radiation or chemicals.

Induced (210)

In replica plating, colonies that grow on the master plate but cannot grow on glucose-salts plate are ___.

auxotrophs (216)

Chemical mutagens can cause which of the following?

base substitutions, frameshift mutations (210)

Mutagens that modify nucleobases change their ___ ___.

base-pairing

Unlike standard DNA polymerases, the DNA polymerase used in SOS repair ___.

can synthesize DNA even in very damaged regions. (214)

Chemicals that cause cancer are called ___.

carcinogens

Two consequences of not repairing damaged DNA in cells include ___.

cell death, cancer (in animals)

Methods of gene transfer in bacteria

conjugation, transformation, transduction

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

frameshift

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.

Mutagens that are DNA segments that insert themselves into genes and inactivate them are called ___.

transposons (210)

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

proofreading, mismatch (207/213)

During repair of oxidized guanine, a DNA glycosylase removes the oxidized nucleobase, leading another enzyme to cut the DNA at this site. Which enzyme then degrades a short stretch of this DNA strand and synthesizes another strand with the proper nucleotides?

DNA polymerase (214)

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

wild

The native or ___ ___ strain describes cells that carry non-mutated DNA

wild type (206)

___ ___ structurally resemble nucleobases and can be mistakenly used when cells make nucleotides, which are then incorporated by DNA polymerase into DNA.

Base analogs (211)

Extensively damaged DNA activates the ___ repair mechanism, which cannot always determine the correct nucleotide sequence, thus mutations resulting from the repair process itself.

SOS

Spontaneous mutations are important because ___.

They allow populations of bacteria to adapt to a changing environment.

___ are segments of DNA that can move from one location to another in a cell's genome.

Transposons

Base ___ structurally resemble nucleobases and can be mistakenly incorporated into nucleotides and then into DNA.

analogs

Selecting penicillin-resistant mutants by plating them on a medium containing penicillin is an example of ___ selection.

direct (215)

Penicillin ___ is a technique in which mutant cells are incubated in glucose-salts broth with penicillin before plating on nutrient agar in order to increase the ratio of auxotrophs to prototrophs.

enrichment (217)

Chemical mutagens that squeeze between base pairs and induce frameshift mutations are called ___.

intercalating agents (212)

The types of damage X-rays can cause to a DNA molecule include:

single-stranded breaks, double-stranded breaks and nucleobase alterations. (212)

True or false: A point mutation involves any substitution of a single nucleotide.

True Pg. 208: "if only one base pair is changed it is a point mutation."

Which of the following types of radiation are mutagenic?

UV, X-rays

___ ___ are a type of radiation that can cause single and double stranded breaks in a DNA strand.

X rays

___ 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 (207)

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

nonsense

Ultraviolet radiation causes a very specific type of DNA damage called ___.

thymine dimers (212)