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BIO207 > Mutations > Flashcards

Mutations Flashcards

1
Q

What are mutations?

A

Heritable changes in the base pair sequence of DNA

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2
Q

What is a forward mutation?

A

Changes wild-type allele to a different allele

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3
Q

What is a reverse mutation/reversion?

A

Changes a mutant allele back to wild-type

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4
Q

What is a substitution?

A

Replacement of a base by another base

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5
Q

What is a deletion?

A

Block of one or more bp lost from DNA

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6
Q

What is an insertion?

A

Block of one or more bp added to DNA

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7
Q

What is a point/base mutation?

A

Change from one base pair to another

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8
Q

What is a missense mutation?

A

Results in new triplet code for different AA

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9
Q

What is a nonsense mutation?

A

Results in triplet code for stop codon

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10
Q

WHat is a silent mutation?

A

New triplet code still codes for the same AA

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11
Q

What is a neutral mutation?

A

Mutation in noncoding region

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12
Q

What is a transition mutation?

A

Pyrimidine replaces pyrimidine or purine replaces purine

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13
Q

What is a transversion?

A

Purine and pyrimidine are interchanged

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14
Q

What causes frameshift mutations?

A

Insertions or deletions of nucleotide(s)

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15
Q

What is the effect of the addition or loss of a nucleotide?

A

Shift in reading frame

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16
Q

What is a loss-of-function mutation?

A

Reduces/eliminates function of gene product

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17
Q

What is a null mutation?

A

Results in complete loss of function

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18
Q

What is a dominant mutation?

A

Results in mutant phenotype in diploid organism

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19
Q

What is a recessive mutation?

A

Loss of function

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20
Q

What is a dominant negative mutation?

A

One allele may encode inactive gene product - interferes with function

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21
Q

What can cause dominant negative mutation?

A

Haploinsufficiency

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22
Q

What are gain-of-function mutations

A

Result in a gene product with enhanced, negative or new functions

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23
Q

Are gain-of-function mutations usually dominant or recessive?

A

Dominant

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24
Q

What is a suppressor mutation?

A

Second mutation that reverts or relieves effects of a previous mutation

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25
Q

What are somatic mutations?

A

Occur in any cell except germ cells

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26
Q

Are somatic cells heritable?

A

No

27
Q

What are germ-line mutations?

A

Occur in gametes

28
Q

Are germ-line mutations inherited?

A

Yes

29
Q

What are autosomal mutations?

A

Occur within genes located on autosomes

30
Q

What are X-linked and Y-linked mutations?

A

Occur within genes located on X and Y chromosome

31
Q

Why is the average mutation rate in gamete-producing eukaryotes higher than that of prokaryotes?

A

Many cell divisions take place between zygote formation and meiosis in germ cells. More chance for mutation accumulaiton

32
Q

How many mutations does each child contain?

A

About 60

33
Q

What is the mutation rate in sperm?

A

2^-4E-8

34
Q

Are mutations more common in sperm from older or younger fathers?

A

Older

35
Q

Are revertants or forward mutations more rare? Why?

A

Revertants. Many mutations disrupt gene function, only a few restore function

36
Q

What is depurination?

A

Hydrolysis of purine base

37
Q

What is deamination?

A

Removal of an amino (-NH2) group

38
Q

What does deamination cause?

A

C -> U
Normal C-G _> A-T after replication

39
Q

How do cosmic rays and X-rays affect DNA?

A

Break backbone

40
Q

How does UV light affect DNA?

A

Forms thymine dimers

41
Q

What is oxidative damage?

A

8-oxodG mispairs with A

42
Q

What does oxidative damage cause?

A

Normal G-C -? mutant T-A after replication

43
Q

What is the proofreading portion of DNA called?

A

3’-to-5’ exonuclease

44
Q

How frequently does DNA polymerase incorporate incorrect bases in bacteria and humans?

A

<10-9

45
Q

What are tautomers?

A

Similar chemical forms of bases that interconvert regularly

46
Q

Give examples of human disease genes with unstable trinucleotide repeats

A

Fragile X syndrome
Huntington disease

47
Q

What are mutagens?

A

Agents that cause DNA damage leading to mutations

48
Q

What are the six classifications of chemical mutagens?

A

Nucleotide base analogs
Deaminating agents
Alkylating agents
Oxidizing agents
Hyoxylating agents
Intercalating agents

49
Q

How does hydroxylation alter DNA?

A

Add an -OH group

50
Q

How do alkylating agents affect DNA?

A

Add ethyl or methyl groups

51
Q

How do intercalators alter DNA?

A

Insert between bases

52
Q

How does the FDA screen for carcinogens?

A

Ames test

53
Q

What is an error-prone DNA repair system?

A

SOS system; microhomology-mediate end-joining (MMEJ(

54
Q

What mechanisms/molecules can reverse DNA base alterations?

A

Alkyltransferase and photolyase

55
Q

Briefly outline the process of base excision repair

A
  1. DNA glycolyases remove altered nitrogenous base
  2. Nearby nucleotides removed
  3. New DNA synthesized to fill gap
56
Q

Briefly outline the process of nucleotide excision repair

A
  1. UvrA + UvrB complex scans for distortions to double helix
  2. UvrB + UvrC complex cuts around damaged DNA
  3. DNA polymerase fills in the gap
57
Q

Why are double-strand breaks harmful for DNA?

A

Can lead to deletions and chromosome rearrangments if left unrepaired

58
Q

What are the two repair mechanisms for double-strand breaks?

A

Homologous recombination. non-homolohous end-joinging (NHEJ)

59
Q

How do bacteria use methyl-directed mismatch repaird?

A

Parental DNA strand marked by adenine methylase where GATC occurs
MutS and MutL bind to mismatched nucleotides
MutH cuts the unmethylated strand oppositve the methylated GATC
Gap made in unmethylated strand by DNA exonucleases
Gap filled in by DNA polymerase using the methylated strand as template

60
Q

Why are parental DNA strands methylated in bacteria?

A

Newly-replicated DNA isn’t methylated, helps spot mistakes

61
Q

What causes Xeroderma pigmentosum?

A

Mutations in any one of secen genes involved in nucleotide excision repair

62
Q

What causes hereditary forms of colorectal cancer?

A

Mutations in mismatch repair genes

63
Q

What causes hereditary forms of breast cancer?

A

Mutations of BCRA1 and BCRA2 which are involved in double-strand break repair by homologous recombination

BIO207 (9 decks)

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