Unit 18- mutations

Question 1

mutations

Answer 1

inherited alterations in the DNA seq
- source of genetic variation
- source of many diseases and disorders

Question 2

adaptive mutation

Answer 2

• genetic variation critical for evolutionary change that brings about adaptation to new environments
• stressful conditions, where adaptation might be necessary to survive, induce increased mutation in bacteria

Question 3

causes of mutations

Answer 3

• spontaneous replication error
• spontaneous chem changes
• chemically induced mutations
• radiation

Question 4

Big categories of mutations

Answer 4

• somatic mutations (all cells derived from that cell with have the mutation)(mitosis)
• germ-line mutations (offspring that came from mutant cell will be completely mutated)(meiosis)

Question 5

base substitution: transition

Answer 5

the substitution of a purine for a purine or of a pyrimidine for a pyrimidine

Question 6

base substitution: transversion

Answer 6

substitution of a pyrimidine for a purine or of a purine for a pyrimidine

Question 7

insertions and deletions: frameshift

Answer 7

affects the reading frame

Question 8

insertions and deletions: in-frame

Answer 8

does not affect the reading frame

Question 9

expanding nucleotide repeats

Answer 9

increase the number of copies of a set of nucleotides (fragile sites)(hairpins. 2/3 bases pairing)

Question 10

forward mutation

Answer 10

wild type —> mutant type

Question 11

reverse mutation

Answer 11

mutant type —> wild type

Question 12

missense mutation

Answer 12

amino acid —> diff amino acid

Question 13

nonsense mutation

Answer 13

sense codon —> stop codon

Question 14

synonymous mutation

Answer 14

change the base but don’t change amino acid

Question 15

silent mutation

Answer 15

codon —> synonymous codon (no change in AA seq!)

Question 16

neutral mutation

Answer 16

no change in function

Question 17

phenotypic effects of mutations

Answer 17

• loss-of-function mutation
• Gain-of-function mutation
• Lethal mutation

Question 18

Suppressor mutation

Answer 18

a mutation that hides or suppresses the effect of another mutation
- Intragenic (second mutation at diff site in SAME GENE hides mutation in another site)
- Intergenic (mutation in second gene that hides mutation in first gene)

Question 19

Factors Affecting Mutation Rates

Answer 19

• Frequency of a change in DNA
• probability that when a change takes place, that it will be repaired
• probability that a mutation will be detected

Question 20

strand slippage

Answer 20

strand loops out when pairing lots of identical pairs, creating an additional nucleotide if new strand or removal of a nucleotide if template strand

Question 21

unequal crossing over

Answer 21

causes crossing over and deletions in the same event

Question 22

radiation

Answer 22

greatly increases mutation rates in all organisms

Question 23

thymine dimer

Answer 23

two thymine bases dimerized (covalently bonded) and block replication

Question 24

SOS system in bacteria

Answer 24

allows bacterial cells to bypass the replication block with a mutation prone pathway

Question 25

Ames Test

Answer 25

used to identify chem mutagens - place mutant bacteria in min medium = no bacteria (control) - mutant bacteria mixed with chem for mutagenic activity. Placed on min medium = lots of bacteria (his- mutant ---> his+ wild type) The chem was mutagenic as it changed the bacteria

Question 26

repair pathways

Answer 26

- mismatch repair - direct repair - base-excision repair - nucleotide-excision repair

Question 27

mismatch repair

Answer 27

- Mismatched bases and other DNA lesions are corrected by mismatch repair. - Enzymes cut out a section of the newly synthesized strand of DNA and replace it with new nucleotides.

Question 28

direct repair

Answer 28

restores the correct structures of altered nucleotides

Question 29

base-excision repair

Answer 29

glycosylase enzymes recognize and remove specific type of modified BASE. Then ENTIRE NUCLEOTIDE is removed, and a section of the polynucleotide strand is replaced.

Question 30

*nucleotide-excision repair

Answer 30

- removes and replaces damaged DNA that distorts the DNA structure - 2 strands of DNA are separated, a section of the DNA containing the distortion is removed, DNA polymerase fills in the gap, and DNA ligase seals the filled-in gap.

Question 31

repair of double-strand breaks

Answer 31

- homologous directed repair: if homology is available (ex: sister chromatids) - nonhomologous end joining: joins any broken ends together, error prone

Question 32

translesion DNA polymerases

Answer 32

allow replication to proceed past bulky distortion in DNA but error prone

Question 33

Transposable elements

Answer 33

sequences that can move about the genome Transposition: movement of the transposons

Question 34

Flanking direct repeats

Answer 34

generated when a transposable element inserts into DNA (staircase cut with transposable ele in middle then flanking fills in both side top and bottom) - both move right

Question 35

terminal inverted repeats

Answer 35

inserted bases around transposable ele that face outward from ele

Question 36

what can transposition take place through?

Answer 36

DNA or RNA intermediate

Question 37

Replicative transposition (copy-paste

Answer 37

- AKA “retrotransposons” - A new copy of the transposable element inserts in a new location, and the old copy stays behind. - Requires reverse transcription to integrate into the target site

Question 38

Nonreplicative transposition (cut and paste)

Answer 38

- AKA “DNA transposons” - The old copy excises from the old site and moves to a new site.

Question 39

Control of transposition

Answer 39

Many organisms limit transposition by methylating the DNA in regions where transposons are common.

Question 40

Transposition in humans

Answer 40

About 45% of the human genome comprises sequences that are related to transposable elements, mostly retrotransposons.

Question 41

Transposons cause mutations by

Answer 41

- Inserting into another gene - Promoting DNA rearrangements Examples - Approximately half of spontaneous mutations in Drosophila - Human genetic diseases - The color of grapes

Question 42

Bacteria: Insertion sequences

Answer 42

Carries only the genetic information needed for transposition

Question 43

Bacteria: Composite transposons

Answer 43

Flanked by two copies of an insertion sequence that may itself transpose

Question 44

Bacteria: Noncomposite transposons

Answer 44

- Lack insertion sequences - Possess a gene for transposase and have terminal inverted repeats

Question 45

Eukaryotic: sim transposons to bacteria

Answer 45

Short inverted repeats - P elements in Drosophila - Ac and Ds elements

Question 46

Eukaryotes: Retrotransposons

Answer 46

- Ty elements in yeast - Copia elements in Drosophila - Alu sequences in humans