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genetics > chapter 7: Mutations > Flashcards

chapter 7: Mutations Flashcards

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Biology 101 flashcards
1
Q

what is a mutation

A

random changes in DNA, bases altered
-environment may favor survival

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2
Q

DNA polymerase performs proofreading and has its own________ fixes bases ______ adding a new base

A

3’-5’ exonuclease activity
-fixes bases before adding a new base

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3
Q

where are errors found?

A

outside of genes

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4
Q

describe the Lauri Delbruck experiment:

A

tested whether or not adaptions derived from selection pressures or if they were random changes in the DNA
-used e.coli and bacteriophage T1 added in generation 4
results:
-if selection pressure theory was correct: certain proportion of generation 4 e. coli cells will be induced at the time of exposure
-mutation theory: number of generation 4 cells resistant to T1 depends on where in the culturing process the random mutation event occurs
* Fluctuation in number of T1 resistant cells does not requre presence of t1

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5
Q

what are the 8 types of mutations

A

-transition
-transversion
-missense
-nonsense
-neutral
-silent
-frameshift
-suppressor

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6
Q

transition mutation

A

A-T to G-C, changes one from one purine - pyrimidine base pair to the other purine - pyrimidine base pair.

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7
Q

transversion mutation

A

C-G to G-C, changes from a purine - pyrimidine bp to the pyrimidine - purine bp.

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8
Q

missense mutation

A

bp change causes a change in mRNA codon so that a different amino acid is inserted.
-change depends where it occurs
-diseases: lesch -nyham syndrome and sickle cell anemia

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9
Q

nonsense mutation

A

change from an amino acid to a stop codon on mRNA
-disease: cystic fibrosis and Duchenne muscular dystrophy

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10
Q

neutral mutation

A

change from an a.a to another with similar chemical properties. it is a type of missense mutation
-no change in protein function, less damaging

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11
Q

silent mutation

A

change in codon does not affect the type of a.a placed.
-the protein is not changed, due to wobble position
-still causes problems: affects the way mRNA folds on itself
-dopamine receptor D2 mRNA: becomes less stable therefore it degrades easier and results in less translation to protein.causes cognitive disorders
-catechol-o-methyltransferase genes: form too strong of folding so translation suffers because it cant be unfolded well. less protein from this gene affects pain tolerance.

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12
Q

frameshift

A

+ or - of one or more base pairs, leads to a shift in the mRNA reading frame
-very damaging
-can generate new stop codons, longer polypeptides, severe alteration in a.a sequence
-diseases: cystic fibrosis and tay sachs
-CCR5 has helped with HIV

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13
Q

suppressor

A

one mutation occurs, a second mutation follows and lightens the effects at a different site.

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14
Q

radiation

A

type of mutation

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15
Q

what are the types of radiation

A

-non-ionizing: usually does not cause mutations, except UV light
-ionizing: energy is sufficient enough to knock an electron out of an atomic shell and break covalent bonds from the creation of ions. penetrates tissues.

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16
Q

describe radiation from UV light

A

-non-ionizing
-produces bulge in DNA strand and disrupts normal pairing of T and A on opposite strands.
-produces thymine dimers

17
Q

what are thymine dimers

A

two adjacent thymines bond next to each other. triggers something wrong in the next cycle

18
Q

non ionzing and ionizing _____ DNA which adds energy

A

strike

19
Q

what are types of ionizing radiation

A

x-rays, cosmic rays, radons

20
Q

describe chemical mutagens

A

can be naturally occurring or synthetic substances that stick to DNA and mutate

21
Q

what are the two types of chemical mutagens

A

-base analogs: chemicals that look like bases in DNA but are not the same.
- used as chemotherapy but can cause cancer
- depend on replication, increases the risk of wrong base
-base modifying agents: dont look like bases but interact and modify them chemically.
- can modify them chemically.

22
Q

intercalating agents

A

-type of mutagen
-adhere to DNA, they dont change the DNA they adhere to but do cause mutations when there is an attempt to copy that section.
- affects the S phase
-can cause additions or deletions = frameshift mutations

23
Q

describe the Ames Test

A

-first step in identifying if a substance is mutagenic.
-reverts mutant strains of bacterium salmonella to the wild type
-his salmonella: usually can make their own histidine. mutated one enzyme that cant make histidine product
-growing salmonella:
1. e. coli in a solution with histidines
2. add to petri dishes. dye diffuses and is exposed to bacteria.
-bacteria results: one bacteria will revert back to normal by chance: can make histidine, results in colonies.

24
Q

site-directed mutagens

A

mutate genes at specific positions, used to investigate the effect on a cell. breaks DNA

25
Q

what are the types of DNA base repair:

A

-DNA excision repair
-nucleotide excision repair
-mismatch repair
-proofreading

26
Q

describe DNA excision repair and the components

A

-removal of base that has been damaged.
-DNA glycosylase: removes damaged purine/pyrimidine. scans and binds where H bonds form. cleaves bond between the damaged base and deoxyribose sugar.
-AP nuclease: cuts deoxyribose backbone 5’ end. cleaves
-DNA exonuclease: 5’ removes backbone: takes out base after excision
-DNA polymerase: fill with correct nucleotide
-ligase: seals

27
Q

nucleotide excision repair

A

repair of dimers, 10 nucleotides removed.
-UVRA (2): away from strands, scan the nucleotides, needed to find the error.
-UVRB: binds to dimer.comes with A
-UVRC: cuts around dimer, binds on opposite strand.
-UVRB and UVR C dislodge and UVRD comes in
-UVRD: dislodges damaged segment on top
-DNA polymerase fills in the gap
-DNA ligase seals the segments

28
Q

mismatch repair

A

repair of perfectly good base pairs, just not a match

29
Q

compare and contrast epigenetics with genetics

A
  • epigenetics: base is not changed, it is modified
  • genetics: changes base
30
Q

what is methyl-directed mismatch repair:

A

-excises incorrect bases, a mismatch between
-typically occurs between palondrinic sequences on the new strand (GATC sequence)
-happens after DNA replication.

31
Q

when does methylation occur on a DNA strand

A

after DNA is copied.

32
Q

describe methylation on the old and new strand of DNA during methyl-directed mismatch repair.

A

-old strand: “correct” strand. methylated, was part of DNA
-new strand: mutated strand, not yet methylated

33
Q

what is involved during methyl directed mismatch repair

A

-Mut S: finds and binds mismatch. there is no h bonding and a bulge between two base pairs.
- Mut H: binds to the nonmethylated GATC, new strand. recognizes GATC but only binds if the other strand is methylated. forms a nick at GATC site
- Mut L: links. brings unmethylated sequence close to the mismatch.
-after nicking by Mut H, exoclucease removes the mismatch of the new DNA strand.
-DNA polymerase fills
-Ligase seals gaps

34
Q

where is methylation distinguished on a GATC strand

A

on the adenine

35
Q

what is an ALU region

A

300 base repeat region
-occurs many times in the genome, makes up 15% of the genome

36
Q

describe class II transposons

A

DNA that “jumps”, re-inserts into another chromosome
-example: hemophilia mutation, codons are interrupted causing a large framshift mutation, blood clotting factor gene is interrupted.

37
Q

describe class I transposons

A

-copy the genes to RNA and a reverse transcriptase converts back to DNA, which is then inserted into new areas of the genome.
-code for their own reverse transcriptase and have regions that code for their own enzymes

38
Q

is HIV a transposon?

A

no, it acts like a class I transposon. reverse transcriptase action

39
Q

what are antibodies and their correlation with transposons?

A

genes for antibodies evolved from transposons.

genetics (9 decks)

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