DNA mutations and repair Flashcards
Distinguish between germline and somatic mutations
Germline mutations occur in germs cells (which give rise to gametes) & are passed onto offspring
Somatic cell mutations occur in somatic (non-gametic) cells) & are not passed onto offspring
mutagens that look like purines and pyrimidines (large, flat, aromatic ring structures) cause mutations by ____ themselves between base pairs, distorting DNA and causing errors in replication
intercalating
What are point mutations? Distinguish between a transition and transversion.
single base pair substitutions
- transition: exchange a purine for a purine or pyrimidine for pyrimidine)
- transversion (substitution of a purine for a pyrimidine or vice versa)
Describe the 3 types of point mutations
Missense: 1 AA is replaced with a different AA
Nonsense: a stop codon replaces a regular codon
Silent: a codon is changed into a new codon but still codes for the same AA
What types of mutations can transposons cause?
insertions, deletions, inversions, and translocations
Insertions and Deletions cause ____ mutations if they don’t occur in a multiple of 3
frameshift
What is an inversion mutation?
when a segment of chromosome is reversed end to end
What is chromosome amplification?
a segment of the chromosome is duplicated
What are translocations?
recombination occurs between nonhomologous chromosomes; creates a gene fusion (a new gene product is made from parts of 2 genes that were not previously connected)
Transposons are aka ____ genes
jumping
All transposons contain the enzyme ____
transposase
Distinguish between an IS element, complex transposon, and composite transposon
IS element: a transposase gene flanked by inverted repeat sequences
complex transposon: IS element but also has additional gene components
composite: 2 similar or identical IS elements w/ a central region between them
2 transposons in the same direction can line up parallel to one another, recombination occurs, and then there is ___ of DNA between the 2 transposons. The original chromosome completely _____ its DNA, which is attached to the transposon that left.
deletion, loses
2 transposons w/ inverted orientation can pair and align, after recombination, the sequence of DNA between the 2 transposons is ____
inverted
A deletion (by a transposon) will cause an individual to become _____ (only one gene copy in the diploid organism
hemizygous
What is loss of heterozygosity?
refers to when all gene expression of the normal gene is lost. This can happen if a transposon deletes a portion of DNA in one allele, and the remaining allele is mutant or defective.
Haploid expression in a diploid organism is _____
hemizygosity
Why are mutations on sex chromosomes typically have a greater effect than mutations on autosomes?
because autosomes have 2 copies of genes, whereas sex chromosomes only have 1 (they’re haploid)
Distinguish between gain of function and loss of function mutations
gain of function: mutation increases activity of a certain gene product, or changes it such that it gains a new and abnormal function
loss of function: result in gene product having less or no function
What is haploinsufficiency?
a diploid organism has only 1 single functioning copy of a gene, and this single copy is not enough to support a normal state
What are the checkpoints in eukaryotes?
G1/S transition and G2/M transition
What is Direct Reversal repair?
repairs UV induced pyrimidine photodimers via visible light
-used by bacteria and many plants (cannot be used by humans)
What is homology dependent repair?
uses other DNA strand as a template
includes excision repair and post-replication repair
Distinguish between excision repair and post-replication repair
excision: occurs before DNA replication; removes defective bases/nucleotides and replaces them
post-replication repair (aka mismatch repair pathway MMR): repairs base pairs that were not repaired by DNA Pol proofreading during replication
How does post-replication repair distinguish between the old and new DNA strand?
In prok., they can use DNA methylation because the newly synthesized DNA strand won’t be methylated yet, only the old DNA strand will be
In euk., they can identify the newly synthesized strand by the free 3’ terminus on the leading strand or by the present of gaps between Okazaki fragments on the lagging strand
What are the 2 pathways that fix double stranded break repairs?
homologous recombination or non-homologous end joining
what is homologous recombination?
one sister chromatid is used as a template to fix the DSB in the other sister chromatid by creating a temporary “joint fusion”
What is nonhomologous end joining?
occurs in cells that aren’t actively growing or cycling through the cell cycle. Broken ends are stabilized and processed, then DNA ligase connects the fragments
-there is no specificity; often results in base pairs being lost or chromosomes being connected in an abnormal way
