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Molecular Biology > Chapter 10 > Flashcards

Chapter 10 Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is independent segregation?

A

?

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2
Q

When are homologs segregated?

A

in anaphase I of meiosis, the pair factors segregated

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3
Q

what is independent assortment?

A

Chromosomes which assort independently

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4
Q

Bateson & Punnett crossed Purple Long peas with red short peas. What did they discover?

A

they allowed the F1 to self-pollinate. Total 381 progeny
• F2 expected ratio: 9:3:3:1
but observed was 12:1:1:2

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5
Q

Because these two sets of factors did not independently assort, there must be some other process going on. What did Bateson & Punnett reason?

A

since the parental types, PL and pl were more common than predicted by independent assortment, there might be a physical coupling joining the two factors. The two genes might be linked.

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6
Q

Barbara McClintock conducted which study?

A

The explanation of linkage and the rearrangement of linked genes came from a study by Barbara McClintock.

studied two traits of corn, both carried on chromosome 9
seed color: C colored / c colorless endosperm texture: Wx waxy / wx starchy

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7
Q

What is jansens hypothesis of crossing over?

A

This result suggests that when a rearrangement or recombination occurs between two genes carried on the same pair of homologous chromosomes, pieces of those chromosomes are exchanged.

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8
Q

When do chromosomes actually come near each other?

A

Meiosis , never in mitosis.

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9
Q

What is it called when chromosomes line up closely making an x shape during meiosis I?

A

chiasmata, named

after the Greek letter chi (X).

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10
Q

Why doesnt recombination disprove the messelson stahl experiment?

A

The Messelson-Stahl experiment showed that DNA replication follows a semi-conservative mechanism. However, this experiment used DNA which had been isolated and broken into pieces about 300 kb long and studied only DNA replication. It did not apply to chromosomes.

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11
Q

What is BDU and how does it work?

A

bromodeoxyuracil(BDU), an analog of thymidine, is used to stain chromosomes differently in the presence of giemsa stain. If BDU is substitied for thiamine in both strands, the chromosome stains light. If BDU is substituted for Thyamine in one strand, the chromosome is stained dark. This is a way to track chromosomes after replication to see how they have dispersed.

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12
Q

can Chromosomal recombination be used as a mechanism of repairing damage to DNA?

A

Yes, in the BDU experiment, These cells were grown mitotically but exposed to a mutagen, and crossing over resulted. NO Mieosis has not occurred, therefore chromosomal recombination can be used as a mechanism for repairing DNA.

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13
Q

Can chromosomal crossing over be used as a mechanisms for repairing damaged DNA?

A

Yes, the BDU experiment proved this when chromosomes were exposed to a mutagen that broke the DNA, yet no meiosis occurred and the color patterns reflected that of recombination.

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14
Q

What are the key steps in homologous recombination?

A
    1. Alignment of homologous DNA molecules
    1. DNA breaks introduced
    1. Stand invasion – short regions of base pairing occur between a ss region of one DNA molecule and the homologous region on the homologous ds DNA molecule. Forms a Holliday junction.
    1. Movement of the Holliday junction.
    1. Cleavage of the Holliday junction and rejoining DNA strands leaving two separate duplex DNA molecules. Called resolution.
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15
Q

Is the holiday model perfect?

A

no, since there could be different genes on “b” and “B” homologous regions, there may be some base pair mismatches!

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16
Q

In the holiday model, What is a splice product?

A

a crossover product in which the ends of the chromosomes are different than original. “reassortment of flanking genes”

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17
Q

In the holiday model, What is a patch product?

A

a non-crossover product with no reassortment. The two DNA molecules have not exchanged ends.

18
Q

Why was the holiday model abandoned?

A

Nowhere in the Holliday model is DNA synthesis required. However DNA synthesis is observed during homologous recombination, so the most favored model is the Double-Stranded Break Model.

19
Q

How does a Single strand lesion end up being repaired by recombination?

A

-When the DNA polymerase on the leading strand meets the lesion and stops, the lagging strand polymerase continues until the fork becomes unstable with a large section of ssDNA.
-The parent strands reanneal, and the fork goes backward or regresses.
-This frees the two daughter strands which can then anneal to each other and form a ds end which can
initiate recombination

20
Q

Do your best to outline the key steps in Double Strand DNA break resulting in recombination?

A
  • Alignment and introduction of breaks.
  • Formation of short ss ends
  • Strand invasion I (by 3’ end of short ss end)
  • Strand invasion II (by other 3’ end of short ss end), Holliday junction formation and synthesis of DNA
  • Holliday junction migration
21
Q

What is the Resolution Patch/Crossover Formation products?

A

You can have non-crossover products in which the ends of the chromosomes are the same.
Or you can have crossover products in which the ends of the chromosomes are different.

22
Q

What is a complication of Resolution Patch/Crossover Formation?

A

You will have gene conversion, which can turn a round species into a wrinked, but you

23
Q

Purposes of Recombination in Prokaryotes?

A
  1. repair ds breaks in DNA
  2. restart collapsed replication forks
  3. allow recombination between chromosomal DNA and DNA from viruses and conjugation
24
Q

What is Chi Site in prokaryotes?

A

GCTGGTGG

25
Q

What is RecBCD, and How is broken DNA processed by RecBCD?

A

It is a helicase nuclease which separates dna at the break; and comps (nuclease activity) it as it moves, until it reaches the Chi site, and then the RecBCD continues to separate but only chomping (nuclease activity) the other strand (not the chi site GCTGGTGG)

whats left is a single stranded end.

26
Q

What is RuvA and RuvB?

A

recognizes holliday junctions and promotes branch migration.

27
Q

What cuts DNA strands at the holliday junction to end recombination?

A

RuvC Resolvase

it can cleave at A/T-T-T-T-G/C
chances it occurring at random is: 1:250

28
Q

in RecA assembly on ssDNA in prep for strand invasion, what happens if RecA binds to a single stranded DNA?

A

Two things, it can very quickly move in the 3’ direction to form an active “rec A” filament to coat 3’ end of ssDNA.
or it can move very slow in the 5’ direction not forming a “recA” filament.

29
Q

What structure is generated by processing a broken DNA molecule by RecBCD?

A

A single stranded end. -and its the one which contained the chi site.

30
Q

Where is recombanition frequency the highest in e. coli DNA?

A

just DOWN (toward 5’ end of chi strand) stream of the chi sites, and there are a lot of chi sites in e. coli.

31
Q

If a virus injects dna, what will recBCD do to it?

A

considering it doesnt have any chi sites, it will chew the whole thing up.

32
Q

RecBCD leaves what type of end?

A

3’ single stranded end

33
Q

RecA can does what to the 3’ single stranded end?

A

Rec A can bind and form a filament on single stranded end….this is weird to me?

34
Q

What happens inside of RecA filament?

A
  • Primary binding site in RecA binds to ssDNA
  • Secondary binding site can bind dsDNA, and is tested for complimentarily compared to the ssDNA in the primary site.
    • if a homology is found, the ssDNA will replace of of the strands in the dsDNA, making a new dsDNA molecule.
  • Base pairing between strands is switched

*keep in mind this will not happen with a single base pair, you must have a complimentary sequence.

35
Q

What are the possible outcomes of ssDNA and dsDNA in the presence of recA?

A

ssCircle + dsLinear = dsCircle + ssLinear

ssLinear + ds Circle = ssLinear duplexed w/ unwound dsCircle (formation of D loop)

dsCircle + dsLinear = rearranged dsCircle + dsLinear

36
Q

What does RuvA and B recognize and do?

A

It recognizes holiday junctions formed by strand invasion and it moves them. “branch migration”

37
Q

What is Ruv C?

A

Ruv C Resolvase is a dimer which binds the holiday junction and clips. Since there are two holiday junctions, each junction can be cut differently creating a patch or splice. it must cut at sequence A/T-T-T-T-G/C, about a 1:250 chance of branch migration.

38
Q

what are purposes of recombination in Eukaryotes?

A
  • Repair ds breaks in DNA
  • Restart collapsed replication forks
  • Required for proper chromosome pairing in meiosis.
39
Q

Describe Meiotic Recombination?

A

Spo11 binds to dsDNA and cleaves it, remaining attached to 5’ end of each break.
MRX comes along and chews back in the 3’ direction while Spo11 is released.
Dmc1 and Rad51 each bind to a single strand of the broken ds, and they form filaments in the 5’ direction of the non-chewed strand (it covers what is exposed by the chewing).
Strand invasion then occurs as the 3’ end of the filament complexes attack a new dsDNA.

40
Q

Try your best to describe the very weird and complicated yeast mating type switching?

A

starting with: dsDNA HMRa w/ “a” info, and dsDNA MATalpha with “alpha” info.
HO cleaves dsMATalpha just after alpha.
Then 5’ resection occurs while alpha region of one strand is chewed back from the 5’ to 3’ end (from 5’ through alpha info) -this can only occur to one strand spatially.
Then Rad51 dependent strand invasion while the middle 3’ end of the chewed strand creates a replication as it attacks dsHMRa (invasion)
Then synthesis of two new DNA strands from the information template at HMRa site while the unused “non chewed” ssMATalpha part is disintegrated. So both new HMRa strands are caused by the invasion of the 3’ end.
The branch migration to disengage duplexes, removal of second old strand at MAT, and repair synthesis and sealing of DNA strands.
Done. the results are dsHMRa w/ “a” info and MATa with “a” info.

Molecular Biology (10 decks)

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