Chapter 15(3) Flashcards
What is a mutation?
a heritable change in DNA sequence
What does mutation produce/what is important about mutation?
it produces genetic variation within populations and is the ultimate source of genetic variation for evolution
Do spontaneous mutations influencing phenotype occur at a high or low rate?
very low rate
Do induced mutations occur at a high or low rate?
can occur at a high rate
When do germline mutations occur?
DNA replication in meiosis
When do somatic mutations occur?
DNA replication in mitosis
What is a point mutation?
mutations that map to a single and specific point (usually a single base pair or a few base pairs)
What is a transition mutation?
type of point-mutation where base pair(S) transition from a purine to a purine or a pyrimidine to a pyrimidine
What is a transversion mutation?
type of point-mutation where a purine transitions from a purine to a pyrimidine or a pyrimidine to a purine
What is an indel mutation?
type of point-mutation that is either an insertion or deletion(we don’t know so we call it an indel)
-can be more than one base pair
What is a silent mutation? What is it also called?
type of point-mutation in protein-coding genes where a base pair is changed, but amino acid stays the same
-also called a synonymous mutation
What is a missense mutation? What is it also called?
type of point-mutation in a protein coding gene where a base pair is changed, which causes a change in the amino acid
-also called a nonsynonymous mutation
What is a nonsense mutation?
type of point-mutation in a protein coding gene where a base pari is altered, causing a new stop codon to be formed
What is a frameshift mutation?
type of point-mutation in protein-coding genes where there is an insertion or deletion of a single pair
Do all mutations have phenotypic consequences?
No
What are spontaneous mutations caused by?
DNA replication errors
What are induced mutations?
mutations caused by mutagens
What is the result of mutations in regulatory regions?
Every one of these six of these
possible mutations reduces (but
does not eliminate) transcription.
Some promoter mutations can
destroy transcription.
What is the approx. mutation rate of DNA replication?
high fidelity with a per bp mutation rate of 1x10^-9
What does strand slippage lead to?
strand slippage in regions of repeating DNA sequence leads to an altered number of repeat elements
-daughter strand slippage forms a hairpin loop
What kind of mutation are trinucleotide repeat disorders? Example?
spontaneous mutations
-ex: huntington disease
What kind of mutation are nucleotide base changes?
spontaneous mutations
What are tautomers?
nucleotide base natural alternative forms
What is the keto form of a nucleotide?
the dominant form and typical base-pairing of nucleotides
What is the enol form of a nucleotide?
less frequent, alternative form of nucleotides that changes the way base-pairing can happen
What happens if DNA replication introduces new nucleotides?
causes a mutation
What can be the result of base pairing with rare tautomers? What kind of mutation is this?
can induce mutations
-it is a spontaneous mutation
What is depurination? What kind of mutation can this lead to?
a spontaneous mutation that results in the loss of a purine
-adenine most commonly incorporated, leading to a transition mutation
What is deamination? Where does this commonly occur? What transition takes place?
a spontaneous mutation that results in the removal of an amino group from a base
-most common at cytosine
-A-T–>G-C
What is are analogs?
induced mutation- some mutagens act as analogs, which are molecules that mimic nucleotides and can replace them by hydrogen-bonding in a double helix
What are Alkylating agent mutagens? What transition takes place?
mutagen that chemically alters the base by adding alkyl groups (methyl or ethyl groups) to positions in the nitrogenous base
-G-C–>A-T
What are Ethyl methanosulfate (EMS) mutagens?
mutagen that adds ethyl groups
-when added to oxygen in guanine, it alters base-pairing and can induce transitions
What is a hydroxylating mutagen? What transition takes place?
adds hydroxyl groups
-C-G–>T-A
Where does slippage most often occur?
in area with repeating nucleotides
What kind of mutagen facilitates slippage?
Intercalating mutagens
What occurs during Intercalation and what does it cause and result in?
-Intercalation distorts the shape of DNA, causing polymerase to “slip” off (slippage).
-When DNA polymerase starts synthesizing, it may miss a base or add an extra one, causing indels.
-These result in frameshift mutations in protein-coding genes
What is Nucleotide Base Excision Repair?
a repair mechanism using the undamaged strand as a template to repair the damaged strand
What it it and what does double-stranded breakage lead to?
it is when DNA damage affects both strands, thus one of them cannot be used as a template to repair the other
-this is deadly and/or leads to big chromosomal alterations, and often to cancer
What are the two-mechanisms that can repair double-stranded breakage?
- nonhomologous end joining
- synthesis-dependent strand annealing
What happens during nonhomologous end joining? Is it accurate?
-This mechanism is initiated in G1
prior to DNA synthesis
-Ku80 and Ku70 recognize
broken ends
-Removing the overhanging
nucleotides can induce mutations
with phenotypic consequences if
they occur in protein-coding genes
or regulatory regions
-No, it is error prone
How is synthesis-dependent strand annealing initiated and how accurate is it?n
-This mechanism is initiated if DNA
has already been synthesized
-This mechanism is an error-free
repair mechanism
