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Molecular Biology - 3550 > chapter 13 exam 2 : recombination > Flashcards

chapter 13 exam 2 : recombination Flashcards

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1
Q

What is homologous recombination?

A

Exchange of DNA through crossing over of homologous chromosomes

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2
Q

What is the function of homologous recombination?

A
  1. Also used for repair, especially double-stranded breaks (DSBs)
  2. Maintaining diversity in sexually reproducing organisms (meiosis)
  3. Mate-type switching
  4. Diversity in avoidance and detection mechanisms
  5. Adaptation of genes to avoid host immune system
    * •Novel invasion proteins
  6. Adaptation of genes to detect pathogens
    * •Novel recognition proteins
    * Antibodies detect antigens. If bacteria change antigens, host needs new antibodies.
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3
Q

Lesions in the template strand lead to 4 outcomes.

A
  1. Continue through the lesions –> perpetuate mutation
  2. Repair is initiated (partial repair) –> DSB
  3. Fork stalling –> wait for repair
  4. Lesion bypass –> single stranded gap
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4
Q

Homologous repair mechanism:

A

1.Create 3’ overhangs
2.3’ end strand invasion via recombinase
•Formation of D loop
3.3’ end strand invasion of other strand invasion
•Formation of D loop
4.Strand extension via polymerase

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5
Q

What are the 2 repair pathways of homologous repairs?

A

1.Synthesis-dependent strand annealing (SDSA)
•Homologs separate
•Finish polymerase and ligase
2. “Classic” DSBR pathway
•Homologs stay together and resolve holiday junctions
1.No crossover
2.Crossover

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6
Q

Holiday junctions are broken via ______

A

resolvase

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7
Q

How is recombination used in meiosis?

A

Recombination is also used to maintain diversity in sexually reproducing organisms

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8
Q

What is crossing over and when does it happen?

A
  • Crossing over happens in prophase I of meiosis I
  • Between homologous chromosomes or homologs
  • 2 homologs have the same genes, but potentially different alleles
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9
Q

2 homologs may have the same _____ but potentially different ______

A

genes ; alleles

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10
Q

When does crossing over occur?

A

Prophase I of meiosis I

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11
Q

What does crossing over occur between?

A

Homologous chromosomes or homologs

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12
Q

Regions of cross over are spaced apart to avoid ________

A

interference

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13
Q

Does crossing over occur between homologs or sister chromatids?

A

homologs, (not sister chromatids)

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14
Q

On average, how many crossovers occur per arm?

A

1

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15
Q

Does cross over have to occur at least once per arm?

A

yes

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16
Q

In meiosis I ______ ______ separate

A

homologous chromosomes

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17
Q

What separates in meiosis II?

A

sister chromatids

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18
Q

What is the result of meiosis?

A

4 unidentical, haploid cells

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19
Q

What does haploid mean?

A

having only one copy of genetic material

20
Q

How is haploid represented?

A

n

21
Q

How is diploid represented

A

2n

22
Q

what does diploid mean?

A

having 2 copies of genetic material

23
Q

Meiotic recombination occurs during what pathway?

A

classic DSBR pathway

24
Q

Does meiotic recombination occur during the SDSA pathway?

A

No, it occurs during the classic DSBR pathway

25
Q

What are the steps of meiotic recombination?

A

1.In early prophase I, double stranded breaks are introduced
•Certain “hotspots” are more commonly broken
•Thus, non-random, but not always predictable
2.3’ overhangs created
3.Strand invasion
4.Extension via polymerase
5.Double cross over intermediate (2 holiday junctions)
6.Resolution
1.Non-crossover (same as SDSA)
2.Crossover

26
Q

What is gene conversion?

A

Nonreciprocal transfer of genetic information

27
Q

What does crossing over maintain?

A

Genetic diversity!

28
Q

What is mitotic crossover?

A
  • Damage during mitosis can lead to crossover events—for the sake of repair
  • SDSA is most common
29
Q

Is SDSA common in meiosis or mitosis?

A

mitotic division

30
Q

Describe DSBR and mating type switching

A

•Yeast (S. cervisiae )exists as 2 possible mate types:
1.Matα
2.Mata
•Yeast can convert between either type through DSBR
•Each mate type is stored as a pseudogene
•HMLα
•HMRa

31
Q

What is used when untimely breaks occur?

A

NHEJ (non homologous end joining)

32
Q

When is NHEJ used?

A

When DSBs occur when homologous chromosomes aren’t available for recombination

33
Q

Describe NHEJ:

A
  • Common in eukaryotes
  • Few prokaryotes
  • Common in G0 and G1
  • Times when homologous chromosomes aren’t paired
  • Mutagenic process = DNA is not the same as it was
  • Loss of function of NHEJ genes promotes cancer
34
Q

Loss of function of NHEJ genes ______ cancer

A

promotes

35
Q

What does a mutagenic process mean?

A

The DNA is not the same as it was

36
Q

When is NHEJ common?

A

eukaryotes, and G0 and G1 (when homologous chromosomes aren’t paired)
- not as common in prokaryotes

37
Q

What are the steps of NHEJ?

A
  1. Recognition of damage via Ku proteins
  2. Cleaning of ends via Artemis •Creation of blunt ends
  3. Creation of 3’ over hang
  4. Polymerase
  5. End joining via ligase
38
Q

What joins the ends in NHEJ?

A

ligase

39
Q

What cleans the ends in NHEJ?

A

Artemis

40
Q

What recognizes damage in NHEJ?

A

Ku proteins

41
Q

What does artemis cleaning the ends in NHEJ lead to?

A

Blunt ends

42
Q

B cells and T cells are immune cells that must recognize an infinite diversity of ______ ______

A

invading proteins

43
Q

Intentional NHEJ called V(D)J recombination creates random novel versions of ______ _____

A

Recognition proteins

- body randomly mixes recognition genes so they are not surprising by novel invading proteins

44
Q

What is another term for recognition protein?

A

antibody

45
Q

How is genome editing used in targeting DSBs?

A
  • used to target DSBs to activate or inactivate or modify genes.
  • used in CRSPR, zinc fingers, and TALENS

Molecular Biology - 3550 (8 decks)

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