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Section 4 > The origins of mutations and DNA replication/repair > Flashcards

The origins of mutations and DNA replication/repair Flashcards

1
Q

What is depurination?

A

bond between base and deoxyribose of DNA spontaneously hydrolyzes; approximately 5000 purine bases (adenine or guanine) are lost ever yday

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2
Q

Approximately 5000 purine bases are lost every day due to what process?

A

depurination

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3
Q

What is deamination?

A

spontaneous conversion of cytosine to uracil

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4
Q

What are pyrimidine dimers?

A

UV light from the sun or elsewhere can cause dimerization of adjacent thymine bases on the same DNA strand..

thymine –> thymine dimer

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5
Q

Explain a somatic mutation (3 concepts)

A
  1. affects only the cell where the mutation occurred and the progeny of that cell
  2. can be problematic if affects proliferation
  3. if mutation occurs in early embryogenesis then the affected individual will harbor a significant amount of mutant cells referred to as mosaicism
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6
Q

Explain the concept of a germline mutation?

A

Will be passed on to offspring

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7
Q

What are the 4 types of mutations (based on levels)?

A
  1. gene mutations
  2. Chromosomal mutations
  3. Genomic mutations
  4. mutations impacting chromatin
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8
Q

What will a miss-segregation of chromosomes during meiosis or mitosis cause?

A

genome mutation

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9
Q

What is the frequency of a genome mutation?

A

10^-2

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10
Q

What results from rearrangements of chromosomes following DNA double stand breaks or faulty recombination?

A

Chromosome mutation

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11
Q

Freq of a chromosome mutation?

A

6 x10^-4

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12
Q

What results from a nucleotide exchange, insertion, or deletion?

A

10^-10

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13
Q

What are the two main ways in which a mutation can alter the nucleotide sequence of a gene?

A
  1. point mutation

2. small insertions and deletions

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14
Q

What is a silent mutation?

A

change in nucleotide sequence does NOT result in a change in AA sequence

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15
Q

What type of point mutation causes a change in nucleotide sequence that does result in a change in the AA sequence?

A

missense

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16
Q

What is a nonsense mutation?

A

change in nucleotide

17
Q

What is a missense mutation?

A

change in nucleotide does result in a change in AA sequence

18
Q

What type of point mutation causes a change in a nucleotide sequence that does not result in a change in the AA sequence of the encoded protein?

A

silent mutation

19
Q

What causes a change in nucleotide sequence destroys an RNA splicing site or generates a novel splicing site?

A

RNA mutant

20
Q

Small insertions or deletions result by 3 distinct mechanisms. What are they?

A
  1. incorrect recombination
  2. strand slippage during replication
  3. intercalating agents
21
Q

What occurs during incorrect recombination?

A

unequal crossing over, which results in loss or addition of genetic material

22
Q

Where is incorrect recombination most likely to occur?

A

at loci that contain repetitive DNA

23
Q

Explain strand slippage?

A

in areas of repetitive sequences, the strand may loop out and slip; causing the DNA replication machinery to copy the strand twice! AH!

24
Q

What do intercalating agents result in?

A

insertions or deletions of one or more nucleotides during DNA replication

25
Q

Insertion or deletion of a number of nucleotides that is not a multiple of three will result in what?

A

frameshift mutation

26
Q

Frameshift mutations account for what % of human genetic diseases?

A

25%

27
Q

In anaphase, what can occur to homologous chromosomes that is bad?

A

Nonjud\sjunction: less to germ cells with surplus or missing chromosomes

28
Q

At the completion of anaphase, the cell divides, giving rise to how many cells with how many chromosomes?

A

2 haploids; 23 chrom

29
Q

What are the 4 types of DNA repair mechanisms?

A
  1. DNA polymerase proofreading
  2. Strand-directed mismatch repair
  3. Base excision repair
  4. Nucleotide excision repair
30
Q

Explain the concept of DNA poly proofreading.

A

3-5 exonuclease activity, re-reads the base pairing and will fix any mistakes

31
Q

Explain strand-directed mismatch repair.

A

A newly synthesized strand contains gaps and nicks which identify the strand and DNA repair mech recognize the distortion in the helix. Enzymes recognize the error and chew it back to the nearest nick, and gap is filled in by DNA poly.

32
Q

What disease is related to stand-directed mismatch repair?

A

Lynch Syndrome/HNPCC: hereditary nonpolyposis colorectal carcinoma; defects in mismatch repair and have a high risk of developing colon cancer

33
Q

Explain base excision repair.

A

DNA glycosylases recognize specific types of altered bases in DNA and catalyze hydrolytic removal

34
Q

Common example of base excision repair.

A
  1. cystosine gets deaminated to uracil.
  2. uracil DNA glycosylase removes the bad base.
  3. The sugar-phosphate backbone remains intact.
  4. AP endonucleases then recognize that a base is missing and cut the sugar phosphate backbone
  5. DNA phosphodiesterase removes the deoxyribose phosphate group and gap is filled in by DNA ploly
35
Q

Explain nucleotide excision repair.

A

repairs damage caused by agents that result in large changes in the structure of DNA. AKA pyrimidine dimers. Repair things recognize distortions; helicase unwraps it; and nucleases cut out the defective strand.

36
Q

Clinical correlation to nucleotide excision repair?

A

xeroderma pigmentosum

37
Q

Describe non-homoglous end joining vs homologous end joining.

A

DNA damaging agents can cause double stranded breaks.

NHEJ: the ends of the double stranded break are cut, resulting in the loss of a nucleotides or nucleotides and put back together

HEJ: recombination processes are used to repair broken DNA; it uses info from one strand to fix the break without losing info

38
Q

What is xeroderma pigmentosum?

A

mutations in nucleotide excision repair; leads to extreme sensitivity of skin to sunglight, pigmentation changes, etc

39
Q

What are 3 inhibitors of DNA replication in chemotherapy?

A

Cytarabine: analouge of cytidine that contains arabinose; competes for binding to DNA poly

Cyclophosphamide; bi-functional alkylating agent; works in the liver and converted to phosphoramide mustard; and inter-intra strands formed with DNA; blocks replication

Doxorubicin: inhibits top II; causing double-stranded breaks to accumulate; strand cant be re-ligated

Section 4 (7 decks)

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