CH 18

homologous recombination repair in the proper sequence

1. DSB is processes at the break site 2.Stand exchange 3.DNA synthesis 4.Resolution and ligation

Examples of mutagens

2-Aminopurine Nitrogen mustard Nitrous acid 5-Bromouracil

Steps in the base excision repair (BER) system

1. N-glycosylase recognizes an abnormal base and cleaves the bond between the base and the sugar 2. AP endonuclease recognizes the missing base and cleaves the DNA backbone 3. DNA polymerase removes the damage DNA and replaces it with normal DNA 4. DNA ligase males a covalent connection in the DNA backbone

Steps in the nucleotide excision repair (NER) system

1. UvrA?UvrB complex tracks along the DNA in search of damage DNA 2. UvrA is released and UvrC binds 3. UvrC makes cuts in both sides of the thymine dimer 4. UvrD removes the damage region 5. UvrB and UvrC are released 5. DNA polymerase fills in the gap and DNA ligase seals the region

base analogs

5-bromouracil 2-aminopurine

Silent Mutation

A mutation that does not change the amino acid sequence of a polypeptide

Forms of tautomers

Enol, Imino, Amino, Keto

What can cause a frameshift mutation? (Check both that apply!)

a base addition a base deletion

base substitution

a change of one base for another

Point mutation

a mutation in which just one base is changed within the DNA

Lethal mutation

a mutation that results in the death of an organism

A translocation that moves a gene from an area of euchromatin to heterochromatin would typically cause _____ in the expression of the gene.

a reduction

Base excision repair (BER) is the main system used in the repair of

abnormal bases

The covalent bond between deoxyribose and a purine base is rather unstable and can undergo a spontaneous reaction with water. The breakpoint of the bond releases the base, and leaves a ____ site in the DNA

apurinic

Cells of the body other than germ-line cells are called ___ cells.

somatic

What can cause a frameshift mutation?

A nucleotide addition and a nucleotide deletion

Which is a base is a transition mutation?

A to G

Order of steps during a typical repair system

Detection - Removal - Replication

Nonhomologous end joining

Double stranded DNA repair in which damaged DNA ends are joined together regardless of homology

Which of the following base changes are transverse mutations?

G to C A to T A to C

Double-strand breaks are typically repaired by which of the following?

Homologous recombination repair and nonhomologous end joining

The following proteins participate in mismatch repair

MutS- Detects the mismatch MutL- Acts as a linker that helps loo the DNA MutH-Makes a cut in a nonmethylated strand MutU-Separates strands at the cleavage site Exonuclease-Digest the nonmethylated strand

Trinucleotide repeat expansion disorders

Myotonic muscular dystrophy Huntington disease Fragile X syndrome

what can cause double-strand breaks (DSBs)?

Reactive oxygen species Gamma rays X-rays

Terms associated with ionizing radiation

Short wavelength High energy Gamma rays

In the mismatch repair system, how is the newly made daughter strand distinguished from the template strand?

The template strand is methylated, while the daughter strand is not.

The phenomenon in which a repeated sequence of these three bases increases in number generation after generation is called

Trinucleotide repeat expansion

The process of replica plating is designed to test if advantageous mutations result in response to the selective agent or were naturally present in the population before selection.

True

Which of the following are examples of ionizing radiation?

X-rays and Gamma rays

Base analogs induce mutations by

being incorporated instead of normal bases during DNA replication

photoreactivation is a repair mechanism that

can directly split a thymine dimer in the presence of light

Mutations that change the configuration of a protein at a specific temperature are called ____ mutations

conditional

A genetic mosaic is an individual that

has regions of the body that are genotypically different from each other is the result of germ-line mutations in both parents

A mutation in a gene that causes an amino acid change in the encoded protein is called a

missense mutation

An individual that has somatic regions with different genotypes is known as a genetic

mosaic

An agent that can change DNA structure and cause mutations is know as

mutagen

An allele that has a DNA sequence different from that of the wild type is called a

mutant allele

The term _____ refers to an inherited change in the sequence of the genetic material.

mutation

The probability that a gene will be altered by a new mutation is referred to as the

mutation rate

Nonsense Mutation

mutations involve a change from a normal codon to a stop codon

Oxidative DNA damage refers to changes in DNA structure that are caused by

reactive oxygen species

Muscle cells, nerve cells, skin cells are examples of

somatic cells

Errors in DNA replication are examples of ____ mutations, while mutations caused by ultraviolet light are _____ mutations

spontaneous; induced

Which of the following does NOT cause double strand breaks (DSBs)?

ultraviolet light

Deamination of cytosines

involves the removal of an amino group from the cytosine base

A reverse mutation

is a mutation that converts a mutant allele back to the wild type form

Some errors create bulky distortions of the double helix. These errors are removed primarily by a DNA repair system called NER, which stands for

nucleotide excision repair

Changes to DNA structure caused by reactive oxygen species are termed

oxidative DNA damage

Which term refers to the imbalance between an organism's production of ROS and the ability to break down?

oxidative stress

The enzyme that can recognize thymine dimers and split them is callled

photolyase

The term germ line is used to described

the cells that produce sperm and eggs

position effect

the effect on the expression of a gene produced by changing its location in a chromosome

In a natural population, a _________-_______ genotype is the most common one

wild type

Nucleotide excision repair (NER) is found in

both prokaryotes and eukaryotes

Examples of somatic mutations include a mutation occurring in a

brain cell embryonic kidney cell adult muscle cell

The complete loss of either a guanine or adenine from DNA is an example of _____

depurination

The removal of a purine from DNA is called

depurination

The Ames test assays whether an agent causes

gene mutations

Reactive oxygen species (ROS) are

products of oxygen metabolism in all aerobic organisms

The strand that is repaired in the mismatch repair system is

the nonmethylated strand

Nonionizing radiation

includes ultraviolet light and contains low energy

The restoration of function by a second mutation at a different site in the same gene is known as

intragenic suppressor

A breakpoint refers to a region

where two chromosomes pieces break and rejoin with other chromosome pieces