Causes of genetic mutations Flashcards

1
Q

what is a mutation?

germline vs somatic mutation?

A

mutation: sudden change in genetic trait. drives allelic variation

somatic: mutation occurs first in the person.

germline: mutation is passed down from one generation to next

somatic mutations can turn into germline mutations

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2
Q

how can you classify types of mutations? explain each type (3)

A

at scale of mutation:

1. genomic change: whole chromosome gain / loss

2. chromosomal change: result from rearrangement of genetic material and give rise to visible structural changes in chr.

  1. gene mutation: vast majority are single base pair changes / small number of base pair changes
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3
Q

what are point mutations?

what are the differnent mutations that are consequences of point mutations(4)?

A

point mutations: change in single base pair mutations. occur in DNA replication errors. most common mutation. substitution, insertion, deletion or inversion of base pairs.

consequences:

a) silent mutation - no change to a.a. sequence

b) missense mutation: changes one a.a. to another (conservative: swaps for a.a. with similar properties, non-conservative: swaps for a.a. with dissimilar properties)
c) Nonsense mutation: creates an early stop codon (creates shorter a.a. highly damaging)
d) frameshift: due to deletion or insertion shifts entire coding sequence by one or more bases due to deletion or insertion of bases

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4
Q

what is a framework mutation?

A

single base is inserted or deleted -> whole reading sequence of a.a. is shifted

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5
Q

name the regions of non-coding DNA that can still affect resulting a.a. sequence

A
  1. regulatory region
  2. splice site
  3. UTR
  4. intergenic regions
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6
Q

what is the change that occurs in Hb S?

A

Single base mutation of Adenine to Thymine. Produces a substitution of valine for glutamic acid at the sixth codon of the beta-globin chain. Hb gene found on chromosome 11

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7
Q

what causes the differences in CF?

which is the most common deletetion in CF?

A

numerous mutations found in CF, causing differences in CFTR.

BUT: different severity of CF disease arise from severity of effect of the mutation of CFTR protein. (most to least: Type 1 -> Type 6)

most common mutation: phenylalanine 508 deletion (deletion of CTT: frameshift mutation = less stable protein)

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8
Q

give an example of disease caused by a frameshift mutation

A

Tay-Sachs disease

  • autosomal recessive disease
  • stops nerves working and is usually fatal
  • mutation in Hex-A gene
  • mutations: 6 deletions, 2 insertions

in Ashkenzai Jew pop: get 4 base pair insertion in exon 11

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9
Q

what are the different types of chromosomal mutations?

A

deletion, duplication (part of a chr breaks off and attaches to sister chromatid), inversions (part of a chr breaks off and reinserts backwards), insertions (part of one getes inserted to another chr), translocation (part of chr breaks off and attaches to different chr)

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10
Q

name two diseaese / disorders from chromosomal mutations?

A

1. Y - chromosome infert: deletetion part of Y-chromsome. called azoospermia factor (AZF) A, B or C

2. Charcot-Marie-Tooth disease (CMT1A): duplication of regions of chr 17. progressive loss of neurons

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11
Q
A
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12
Q

what are non-disjunction diseases?

A

Nondisjunction means that a pair of homologous chromosomes has failed to separate or segregate at anaphase so that both chromosomes of the pair pass to the same daughter cell.

lead to:

gain or loss of whole chromosomes. e.g. Down Syndrome: trisomy

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13
Q

what causes genetic mutations?

A

spontaneous mutations

induced (environmental) mutations (e.g. radiation, chemicals, infectious agents)

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14
Q

what are someo of the different mechanisms of spontaneous mutations?

A

1. tautomeric shift (base substitution)

2. depurination

3. deamination

(4. errors in proof reading
5. depyrimidation (very low occurance)
6. oxidation )

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15
Q

what are tautomers?

A

tautomers: all DNA bases (CTAG) have different forms depending on their position on the atoms

  • common form of of bases are amino (C&A) and keto (G & T) forms. But sometimes can get rare form of base pairs: imino (C’ & A’) and enol (G’ & T’).
  • (C’ binds with A, T’ binds with G, A’ binds with C, G’ binds with T)
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16
Q

what is a tautomeric shift?

  • what is the number of a) wild types b) mutants of the DNA exist that occur after second generation progeny after a tautomeric shift?
A

tautomeric shift:

  • when a tautomer occurs in DNA replication, the imino or enol pairs with non-complementary base -> base sub
  • BUT: after the first DNAreplication occurs, the BP that was a tautomer reverts back to its stable form. HOWEVER, the the other non-complementary BP stays! (the mutation)

result: in 3x wild type, 1 mutant. transition mutation. means can go undetected as shape of protein doesnt really change

17
Q
A
18
Q
A
19
Q

what is depurination mutation?

A
  • loss of a purine base (A or G)
  • leads to deletion mutation

(can occur in double DNA helix)

20
Q

what is a deamination mutation?

A
  • removal of the amino (-NH3) group through hydrolysis water
  • leads to substitution reaction
21
Q

what are most deamination and depurination errors corrected by?

A

polymerase enzymes

22
Q

what is a mutagen?

A

things that increase mutation rates:

  • physical factors (heat, radiation)
  • chemical factors (nicotine, pesticides)
  • infectious agents (bacteria, viruses)
23
Q

how does UV radiation cause direct mutations?

A

direct damage

  • cause DNA phoshpate backbone to break
  • break BP connections
  • alter bases
  • cause intra-/inter- stand cross links
24
Q

how does UV radiation cause indirect mutations?

A

indirect effects: ionizing radiation creates free radicals that damage DNA by reacting with it

25
Q

what is the effect of DNA damage by UV radiation to melanocytes?

A

in melanocytes: pyrimindine dimers -> formed when cyclobutane rings occur between adjacent, same strand pyrimidines in DNA

  • (disrupts p53 gene (tumour supressor))
26
Q

what does smoking do to DNA strands?

A

causes double stranded breaks and base pair transversions (more deletarious types)

27
Q
  • name two infectious agents that can cause DNA mutations
  • describe how they work
A

Helicobacter pylori: causes stomach cancer. 50% of pop. is infected. causes mutation rate of stomach cells to increase by 2-8% higher spontanous rate. also get epigenetic changes. DNA repair loss

Human papilloma virus: common sexually transmitted virus. viral DNA incorporated into host. produces protein called E6. E6 binds to p53 (tumour supressor) and directs p53 for degradation. disables normal DNA damage repair processes