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
