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EOM Test 2 > DNA Repair and Recombination > Flashcards

DNA Repair and Recombination Flashcards

1
Q

What is Xeroderma Pigmentosum?

A

Disorder caused by a defect in the DNA repair pathway nucleotide-excision repair

Uv Sens., excessive freckling, skin cancers, corneal ulcerations

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2
Q

What are three types of repair mechanisms?

A
  • Repair involving excision of lesion followed by replacement
  • Direct repair
  • Double-stranded break repair
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3
Q

What is the mechanism of mismatch repair?

A

Endonuclease nicks the strand, followed by exonuclease degradation.

DNA Pol III and DNA ligase fill in the lost DNA

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4
Q

What is the cause of HNPCC or Lynch syndrome?

A

Mutations in the mismatch repair mechanism.

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5
Q

What are Mut proteins?

A

Proteins responsible for recognizing the mismatch and identifying the methylated parent strand.

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6
Q

How are pyrimidine dimers formed?

A

UV light causes adjacent pyrimidines to dimerize (mostly thymines)

interfere with replication and transcirption

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7
Q

What fixes pyrimidine dimers?

A

Photoreactivation or nucleotide-excision repair

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8
Q

What is nucleotide excision repair?

A

Repairs damage resulting in large distortions of the DNA double helix (e.g. pyrimidine dimers)

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9
Q

What is excinuclease?

A

UV-specific endonuclease

Defect in this enzyme is the cause for Xeroderma Pigmentosum

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10
Q

Why does DNA contain thymine and not uracil?

A

Uracil is readily produced by chemical degradation of cytosine, so having thymine makes detection and repair more efficient

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11
Q

What is depurination?

A

Loss of base leaving just the phosphate and sugar.

Creates an abasic site

Higher rate for purines

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12
Q

What is the mechanism of Ricin?

A

Acts by depurination of adenine in rRNA

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13
Q

What is Base-excision repair?

A

Repairs altered bases resulting fro spontaneous changes and environmental insults

Primarily responsible for removing small, non-helix-distorting base lesions

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14
Q

What is spontaneous deamination?

A

Spontaneous deamination of a base

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15
Q

What is the function of Deoxyribose phosphate lyase?

A

Removes the base free phosphate residue so that the insult can be repaired

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16
Q

What is MBD4?

A

glycosylase employed in an initial step of base excision repair

binds to fully methyated CpG sites and their altered DNA bases

17
Q

What is Direct Repair?

A

A specific enzyme (methyltransferase) repairs the damage, rather than using a set of enzymes

Does not involve DNA polymerase

18
Q

What causes double stranded breaks?

A

High-energy radiation

Oxidative free radicals

19
Q

What are the two mechanisms of double stranded break repair?

A

Nonhomologous end-joining repair (more error prone of the two)

Homologous recombination repair

20
Q

What are BRCA1 and BRCA2?

A

Genes implicated in breast and ovarian cancer

Involved in homologous recombination repair

21
Q

What is DNA recombination?

A

The rearrangement or exchange of genetic information between two DNA molecules or between two different parts of the same DNA molecule

22
Q

What is the difference between legitimate and illegitimate DNA recombination?

A

Legitimate - fidelity is preserved, no information lost (crossing over)

Illegitimate - fidelity is not preserved

23
Q

What is a Holliday Junction?

A

Junction between recombined portions of two homologous chromosomes

24
Q

What is the result of unequal crossing over?

A

insertion or duplication in one strand, and deletion in the other

25
Q

What contributes to unequal crossing over?

A

Short repetitive sequences

Similar regions in different genes

These sequences confuse annealing

26
Q

What are Alu sequences?

A

Transposable elements within the genome that can act as disease markers

27
Q

What diseases are linked with Alu insertions?

A 
Breast Cancer
Ewing's sarcoma
Familial hypercholesterolemia
Hemophilia
Neurofibromatosis

EOM Test 2 (20 decks)

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