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Genetics > CH 9: DNA Replications and Recombination > Flashcards

CH 9: DNA Replications and Recombination Flashcards

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1
Q

Conservative, dispersive, semiconservative replication models

A

conservative - entire double stranded DNA molecule serves as a template, end up with a fully conserved DNA molecule and a new one

dispersive - both strands break into fragments to serve as templates and then reform into two complete DNA molecules containing both old/new fragments

semiconservative - each DNA strand serves as a template for a new DNA molecule

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2
Q

What was Meselson and Shahl’s findings?

A

E. coli has semiconservative replication

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3
Q

What are replicons?

A

segments of DNA that undergo replication, includes replication origin

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4
Q

What is theta replication in E. coli? What direction?

A

replication of circular E. coli DNA, has one origin of replication and two replication fork in a bidirectional replication

circular DNA replication, 2 strands unwind and form replication bubble and replication continues until both replication forks meet

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5
Q

How does linear replication occur in eukaryotic replication?

A

multiple origins of replication form replication bubbles, DNA synthesis occurs and forks move outwards, forks merge with one another and DNA segments fuse, create two identical linear DNA molecules

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6
Q

Theta vs linear eukaryotic replication

A

DNA template - circular vs linear
Breaking nucleotide strands - does not occur
Number of replicons - 1 vs many
Uni vs bidirectional - either vs bidirectional (opposite directions on leading lagging strands but still goes 5’-3’)
Products - 2 circular molecules vs two linear molecules

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7
Q

What is required for linear eukaryotic replication (3)?

A

template strand, nucleotides, enzymes and proteins

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8
Q

What direction does DNA polymerase move?

A

5’ → 3’

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9
Q

Phosphodiester bonds

A

link backbone of two adjacent sugars on DNA strand

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10
Q

DNA polymerase only adds nucleotides to the ? end of a growing strand. Replication occurs in ? direction. How is continuous and discontinuous replication present in replication?

A

3’, 5’ → 3’
leading strand - continuous
lagging strand - discontinuous Okazaki fragments

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11
Q

What is the relationship between direction of replication on leading and lagging strand?

A

antiparallel on opposite strands

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12
Q

Prokaryotic and eukaryotic cells have what 3 things for replication?

A

initiator proteins, DNA polymerase, run in 5’ → 3’ direction

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13
Q

What is the initiator protein in E. coli? What is the origin replicon called?

A

DnaA in E. coli binds to oriC and causes a section of DNA to unwind

oriC is the initiation site for origin replicon

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14
Q

What associated proteins and enzymes are part of unwinding in bacterial cells?

A

iniator protein - starts unwinding
DNA helicase - breaks hydrogen bonds between bases of two nucleotide strands of a DNA molecule
ssbs - prevent strands from snapping back together
DNA gyrase/ topoisomerase - prevents supercoiling and relieves torsional strain

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15
Q

E. coli and in bacteria requires ? to separate DNA strands before helicase can attach.

A

initiator

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16
Q

During elongation what is single strand DNA used as?

A

a template for DNA synthesis

17
Q

What is primase? What are primers?

A

primase makes short RNA sequences that are primers

primers are short RNA strands that have a 3’-OH group so DNA polymerase can attach and start adding nucleotides

18
Q

How are primers utilized in leading and lagging strands?

A

leading is continuous - one primer needed
lagging is discontinuous - new primer for each Okazaki fragment

19
Q

What enzyme is elongation carried out by? What are the 5 components to an active replication fork?

A

DNA polymerase III

  1. helicase - unzip DNA
  2. SSBPs - prevent secondary structures
  3. DNA gyrase - decrease torsional strain
  4. primase - make primers with 3’-OH group at beginning of each DNA fragment
  5. DNA pol III - synthesize leading and lagging nucleotide strands
20
Q

What are the functions of DNA pol I and ligase?

A

DNA pol I - removes and replaces primers
ligase - zaps gaps when primers are removed and new nucleotides are put in

21
Q

Exonuclease activity - DNA pol I vs III

A

exonuclease activity - correcting polymerase errors
DNA pol I - 5’-3’ and 3’-5’ activity
DNA pol III - 3’-5’ activity

DNA pol I - removes and replaces RNA primers with DNA
DNA pol III - elongates DNA

22
Q

What functions of E. coli’s DNA polymerases have in common?

A

make complementary seq to template that is antiparallel

use dNTPs to make new DNA

5’-3’ direction adding nucleotides to 3’-OH group

catalyze phosphodiester bond by joining 5’ phosphate group to 3’-OH group of previous nucleotide

works with many proteins

23
Q

Exonuclease activity engages in proofreading. What direction is proofreading? What enzyme? What is mismatch repair?

A

3’ - 5’ by DNA polymerase I

enzymes excise incorrect nucleotides and replace them after replication is complete

24
Q

Termination in different cells, ex. E. coli

A

some molecules end when replication forks meet

E. coli requires termination protein TUS to bind to Ter site to form a complex

25
Q

What initiates replication in eukaryotic cells? What does ORC do?

A

ORC (origin replication complex) binds to origins of replication and recruits helicase to unzip DNA

26
Q

Yeast and ARS, autonomously replicating sequences

A

yeast has region called ARS where the ORC (origin replication complex) binds to start replication

27
Q

Two main steps of initiation in DNA rep

A
  1. origins are licensed and approved to rep - replication licensing factors bind to each origin

ORC (origin recognition complex) attaches to each origin of replication, MCM (minichromosome maintenance) and CDC-45 is needed for initiation to start

  1. rep machinery initiates rep at each licensed origin
28
Q

DNA pol a, delta, epsilon

A

a - enzyme associated with primase to add nucleotides during initiation (not progressive - falls off of DNA template before rep)

delta - lagging strand
epsilon - leading strand
d+e are progressive - can stay on DNA template during replication

29
Q

What do histone form?

A

nucleosomes - units of 8 histone proteins

30
Q

Telomeres and telomerase, what is the end replication problem?

A

telomerase - RNA protein enzyme that extends 3’ end of chromosome, binds to end of chr and adds new DNA so chr. doesn’t shorten

telomeres - repetitive DNA sequences

end replication problem - DNA replication would leave gaps at the end of the chr and chr would shorten each time the cell divides

this is mediated through telomerase extending DNA and filling in gaps formed when the RNA primer is removed

Genetics (3 decks)

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