DNA mutations and repair

Question 1

Distinguish between germline and somatic mutations

Answer 1

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

Question 2

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

Answer 2

intercalating

Question 3

What are point mutations? Distinguish between a transition and transversion.

Answer 3

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)

Question 4

Describe the 3 types of point mutations

Answer 4

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

Question 5

What types of mutations can transposons cause?

Answer 5

insertions, deletions, inversions, and translocations

Question 6

Insertions and Deletions cause ____ mutations if they don’t occur in a multiple of 3

Answer 6

frameshift

Question 7

What is an inversion mutation?

Answer 7

when a segment of chromosome is reversed end to end

Question 8

What is chromosome amplification?

Answer 8

a segment of the chromosome is duplicated

Question 9

What are translocations?

Answer 9

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)

Question 10

Transposons are aka ____ genes

Answer 10

jumping

Question 11

All transposons contain the enzyme ____

Answer 11

transposase

Question 12

Distinguish between an IS element, complex transposon, and composite transposon

Answer 12

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

Question 13

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.

Answer 13

deletion, loses

Question 14

2 transposons w/ inverted orientation can pair and align, after recombination, the sequence of DNA between the 2 transposons is ____

Answer 14

inverted

Question 15

A deletion (by a transposon) will cause an individual to become _____ (only one gene copy in the diploid organism

Answer 15

hemizygous

Question 16

What is loss of heterozygosity?

Answer 16

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.

Question 17

Haploid expression in a diploid organism is _____

Answer 17

hemizygosity

Question 18

Why are mutations on sex chromosomes typically have a greater effect than mutations on autosomes?

Answer 18

because autosomes have 2 copies of genes, whereas sex chromosomes only have 1 (they’re haploid)

Question 19

Distinguish between gain of function and loss of function mutations

Answer 19

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

Question 20

What is haploinsufficiency?

Answer 20

a diploid organism has only 1 single functioning copy of a gene, and this single copy is not enough to support a normal state

Question 21

What are the checkpoints in eukaryotes?

Answer 21

G1/S transition and G2/M transition

Question 22

What is Direct Reversal repair?

Answer 22

repairs UV induced pyrimidine photodimers via visible light

-used by bacteria and many plants (cannot be used by humans)

Question 23

What is homology dependent repair?

Answer 23

uses other DNA strand as a template

includes excision repair and post-replication repair

Question 24

Distinguish between excision repair and post-replication repair

Answer 24

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

Question 25

How does post-replication repair distinguish between the old and new DNA strand?

Answer 25

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

Question 26

What are the 2 pathways that fix double stranded break repairs?

Answer 26

homologous recombination or non-homologous end joining

Question 27

what is homologous recombination?

Answer 27

one sister chromatid is used as a template to fix the DSB in the other sister chromatid by creating a temporary “joint fusion”

Question 28

What is nonhomologous end joining?

Answer 28

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