Chapter 8 - Mutations and Repair Flashcards
What is a mutation?
Permanent change in DNA sequence.
Mutations are defined as a permanent change.
What happens in forward mutations?
It alters wild-type alleles and is usually random and harmful.
What happens in reverse mutations?
It restores wild-type alleles and can counteract previous damages.
What can cause mutations?
Spontaneous degradation of nucleotides and DNA damage from chemicals, radiation, or free radicals.
Why might nucleotides spontaneously break apart?
Due to spontaneous depurination or hydrolysis.
How can the causes of mutations be categorized?
They can be placed on a large scale or small scale.
What are examples of small scale mutations?
Base substitutions, insertions, and deletions.
What are examples of large scale mutations?
Errors in Meiosis and Mitosis causing chromosomal deletions and duplications.
What are the types of mutations?
Point mutations –> Single nucleotide subs –> transition and transversion, insertion, and deletion.
What is a transition mutation?
Purine for purine or pyrimidine for pyrimidine substitution.
What is a transversion mutation?
Purine for pyrimidine or vice versa.
What are insertion and deletion in genetics?
Additions or losses of nucleotide pairs in a gene.
What is strand slippage?
A genetic process in which deletions and insertions of small contiguous repeats occur because of misalignment between DNA strands. This causes parts of template DNA to be copied more than once or to be missed during DNA replication.
What is DSB in the context of DNA?
Double-strand break, where both strands of the DNA molecule are broken.
What can cause double-strand breaks in DNA?
Chemical exposure, radiation, or spontaneous events.
What are hypotheses for the origin of bactericide resistance?
- Resistance is a physiological response to a bactericide. 2. Resistance arises from random mutation.
Explain the mutation rates.
Mutations are random and occur at a constant low rate.
Only mutations in ________ can be passed to offspring.
Sperm or egg cells.
Where are mutation rates high?
In eukaryotes and low in prokaryotes.
What raises the risk of mutations?
Cell divisions, metabolic activity, radiation, age, and exposure to chemicals.
What are the causes of spontaneous mutations?
Depurination, deamination, base tautomerization, and polymerase copying error.
What is depurination?
Purines fall off the nucleotide and occurs 1000 times a day.
What is deamination?
When an amine group is removed from a base.
What is tautomerization?
Structural isomers that spontaneously change and make base pairs connect incorrectly.
What can DNA damage-induced mutations lead to?
Transversions and oxidation of guanine.
What type of radiation is known to cause DNA damage?
Ionizing radiation.
What type of DNA damage can ionizing radiation cause?
Double-Strand Breaks (DSB).
What are some potential consequences of DNA damage from ionizing radiation?
Deletion, cell death, chromosomal rearrangements.
What is a characteristic of repair pathways for DNA damage caused by ionizing radiation?
They were error-prone.
What does UV irradiation cause?
DNA damage in the form of thymine dimers.
What is Fragile X syndrome associated with?
Repeats of CGG (20-50).
What happens to alleles with more than 56 repeats in Fragile X syndrome?
They are unstable and prone to expansion.
What is the result of having more than 200 repeats in Fragile X syndrome?
It results in a nonfunctional FMR1 gene.
What type of genetic change is involved in Fragile X syndrome?
Trinucleotide repeat expansion/contraction.
What is the normal range of CAG repeats in the HD allele?
6-28 repeats.
What characterizes pre-mutation alleles of Huntington Disease?
They have more than 28 repeats of CAG.
What happens when there are more than 36 CAG repeats in the HD allele?
It leads to GoF alleles that build up and kill neurons.
What genetic phenomenon is associated with Huntington Disease?
Trinucleotide repeat expansion.
What is trinucleotide repeat expansion?
When a segment of DNA containing three nucleotides is repeated multiple times.
What is trinucleotide repeat contraction?
The number of repeats in sequence decreases.
What are examples of large-scale mutations?
Deletion, amplification, chromosomal rearrangement.
What is deletion in large-scale mutations?
Large chunks of chromosomes lost permanently.
What is amplification in large-scale mutations?
Duplication of a big chunk of chromosome.
What is an insertion in chromosomal rearrangements?
A piece of chromosome moves to another one.
What is an inversion in chromosomal rearrangements?
A piece of chromosome gets ‘reversed’.
What is a translocation in chromosomal rearrangements?
Two pieces of chromosomes switch.
What are small scale mutations?
Insertions, deletions, and substitutions.
What are insertions in small scale mutations?
Extra bases added to DNA sequence.
What are deletions in small scale mutations?
Bases removed from DNA sequence.
What are substitutions in small scale mutations?
Alteration in DNA sequence with no +/- bases.
What happens when a mutation disrupts a splice site in introns?
It can lead to non-silent mutations.
What can mutations in introns create?
New splice sites.
Why can some mutations in introns have an effect?
Because some introns contain RNA genes.
What is a synonymous mutation?
No change in amino acid.
What is a non-synonymous mutation?
Change in codon.
What is a nonsense mutation?
Premature stop codons, usually kills proteins.
What is a missense mutation?
Creates change in an amino acid.
What is a conservative missense mutation?
Causes little or no change in protein function.
What is a nonconservative missense mutation?
Alters protein function, usually negatively.
What is a point mutation (substitution)?
One nucleotide is replaced with a different nucleotide.
What is a frameshift mutation?
Insertion and deletion, usually drastic.
What is the effect of a loss of function mutation?
Protein is less functional and recessive.
What is the effect of a gain of function mutation?
Always dominant.
What is a hypermorph mutation?
Highly expressed.
What is a neomorph mutation?
Entirely new function or in new tissue.
What is a dominant negative mutation?
Even with one allele, it overcomes the other.
What is an antimorph?
A gain of function mutation that acts in opposition to the normal gene’s function.
What is an isomorph?
Silent point mutations.
What is the function of alkyltransferase in DNA repair?
Remove ethyl and methyl groups.
What is the role of photolyase in DNA repair?
Reverse dimers.
What does Base Excision Repair (BER) do?
Removes altered nitrogen bases.
What is the purpose of Nucleotide Excision Repair (NER)?
Removes nucleotides.
What is Non-Homologous End Joining?
A DNA repair mechanism that joins broken ends without needing a homologous template.
What characterizes Microhomology-Mediated End Joining?
It is an error-prone DNA repair mechanism.
Most mutations do not affect
Phenotype
