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BIOL 2311 > Chapter 14- Part 2 DNA Replication Models > Flashcards

Chapter 14- Part 2 DNA Replication Models Flashcards

1
Q

What is the Watson-Crick model of DNA replication?

A

Semi-conservative model of DNA replication.

H Bonds break between nitrogenous bases to allow strand separation.

Each DNA strand is a template for the synthesis of a new strand.

Template (parental strand) determines the sequence of bases in the new strand (daughter) = complementary base pairing rules.

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2
Q

Briefly describe the semi-conservative model of replication.

A

H Bonds break between nitrogenous bases to allow strand separation.

Each DNA strand is a template for the synthesis of a new strand.

Template (parental strand) determines the sequence of bases in the new strand (daughter) = complementary base pairing rules.

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3
Q

What is the replication fork?

A

Like a zipper it breaks the H-bonds between nitrogenous bases to create a template.

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4
Q

What are the other two models of replication, in addition to the semi-conservative model?

A

COnservative replication model- The two strands of the original molecule serve as templates for the two strands of a
new DNA molecule; then, they rewind into an all “old” molecule.

Dispersive Replication model- Neither parental strand is conserved, and both chains of each replicated molecule
contain old and new segments.

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5
Q

What is the conservative model of replication?

A

The two strands of the original molecule serve as templates for the two strands of new DNA moleclel then, they rewind into an all “old” molecule.

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6
Q

What is the Dispersive replication model?

A

Neither parental strand is conserved and both chains of each replicated molecule contains old and new segments. They are broken off and combined together so it may require a lot of energy and coordination from the cell,

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7
Q

In the Meelson and Stahl experiment, what were bacterial cells grown in?

A

Heavy nitrogen 15N, thus DNA incorporated 15 N

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8
Q

Where was 15 N used in DNA?

A

In nitrogenous bases so 15N was incorporated 15 N after multiple rounds of replication.

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9
Q

What did meselson and Stahl do after DNA incorporated n15 in its nitrogenous bases?

A

They switched cells to media containing lighter 14N.

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10
Q

What was done after switching the cells to n14 from n15 in the MS experiment?

A

Small samples of DNA were extracted at
various time intervals.

0 min 0 Rounds of replication

20 mins. 1 round or replication

40 mins 2 rounds of explication

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11
Q

What were the three intervals where MS took DNA smples in n14 medium?

A

0 min 0 rounds
20 mins 1 round
40 mins 2 rounds

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12
Q

What was the DNA structure when the first DNA sample was taken in MS?

A

Takeen IMMEDIATLEY after switching E.coli from N15 to N14 at 0 mins.

We still had both strands of DNA at N15.

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13
Q

What was the DNA structure when the second. DNA sample was taken?

A

Taken after 20 mins, after 1st round o d replication.

DNA molecule had one strand of N15(parent) and one strand of N14(daughter).

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14
Q

What was the DNA structure when the third. DNA sample was taken?

A

Taken 40 mins after.

2 DNA molecules(bands)- One had N15(OG parent) /N14(new daughter)

And one lighter N14 (OG daughter) and another N14 new daughter)

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15
Q

What did they do with each sample in MS experimentally?

A

They extracted the DNA from bacterial cells and centrifuged it to create a Density Gradient.

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16
Q

What is a density gradient?

A

Shows heavy molecules on bottom and light molecules on top.

Created by Celsium Chloride.

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17
Q

How did the centrifuge the extracted DNA?

A

Once creating a density gradient using Celsium Chloride, they centrifuged the molecule for 48 hours.

At the end of centrigugation, the DNA positioned it self on the gradient according to its own density.

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18
Q

At 0mins and 0 rounds of replication in MS, what are the # of bands, location, and Compostion of all replication models?

A

In Semiconservative model: 15/15 bottom of time 1 band

Conservative: 15/15 bottom of tube, 1 band

Dispersive: 15/15, bottom of tube, 1 band

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19
Q

At 20 mins and 1 round of replication in MS, what are rhe # of, location and compostion bands in all replication models?

A

Semi: One band 15/14 center of the tube

Conservative: Two bands 14/14 top and 15/15 bottom [DOES NOT MATCH EXPERIMENTAAL RESULTS]

Dispersive: One band 15/14 center of tube

Because both Semi and DIspersive contain strands of both N15 qand N14 parental and Daughter DNA strands.

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20
Q

What model of replication is eliminated after one round of replication in MS?

A

Conservative: two bands 14/14 top and 15/15 bottom [DOES NOT MATCH EXPERIMENTAL RESULTS]
therefore eliminated

They are fixed and replicated

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21
Q

At 40 Mins and 2 round of replication what are the number of, location of, composition of the bands in replication models?

A

Semi: Two bands 14/14 top
14/15 bottom

Dis: one band more of n14 closer to top

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22
Q

Why only one strand in DISpersive model in 2nd replication in MS?

A

Only one strand because still have hybrid density but more n14, little bit more closer to the top of the tube [does not match experiment)

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23
Q

How does Semiconservative match at 2nd round of replication?

A

Two bands:

OG N15 + New Daughter N14 Middle
OG Daughter N14 + New Daughter N14 TOP

24
Q

What was the conclusion of MS experiment?

A

DNA Replication is Semiconservative

25
Q

DNA polymerases assemble complementary polynucleotide chains from what?

A

Individual deoxyribosenuecleotides: dATP, dGTP, dCTP, dTTP

26
Q

What are the four different deoxyribosenucelotide triphosphates one for each base?

A

DATP, DGTP, dCTP, dTTP

27
Q

To what end does DNA polymerase adds a nucleotides to?

A

The exploded 3’ OH end of an existing nucleotide chain

28
Q

DNA polymerases only assemble nucleotide chains in what direction?

A

5’ to 3’ direction

29
Q

What is exposed at the oldest and newest end of ta new DNA strand?

A

oldest- 5’ triphosphate
newest- 3’ OH hydroxyl

30
Q

Why is the template strand “read” in the 3’ to 5’ direction?

A

Because DNA strands run anti parallel to each other

31
Q

What should the incoming nucleotide be when adding onto the 3’ OH end when the complementary pair is Thymine? What molecule checks this is correct?

A

DATP. DNA polymerase.

32
Q

What molecule checks if the incoming nucleotide is correct or not according to complementary base pairing?

A

DNA polymerase

33
Q

Explain what happens to the triphosphates in deoxyribosenuceleotides?

A

One of the phosphates is forms a bond with the 3’ OH group of the previous nucleotide and for the other 2 hydrolosis provides energy for DNA chain elengoation reaction.

34
Q

What 3 things does DNA replication require?

A

Something to copy- parental DNA molecule(Template)

Something to do the copying- enzymes(DNA polymerases)

Building blocks to make a copy- Nucleotide Triphosphates- dATP, dTTP, dGTP,dCTP

35
Q

DNA polymerase can only add a nucleotide to what end?

A

only to the 3’ end with the exposed OH group of an existing nucleotide chain

36
Q

DNA polymerase adds whar?

A

Adds a single nucleotide derived from the nucleotide triphosphates

37
Q

Accordance to the HAND model of DNA polymerase+ Sliding clamp what is the palm represent?

A

Polymeraziation reaction active site

38
Q

Why was the sliding clamp created?

A

Because DNA is so long and needs to be meticously copied in 9 hours we need to maximize effiency.

39
Q

What does the sliding clamp do?

A

Attached to the rear DNA polymerase, making sure DNA polymerase does not fall off the template- increasing rate of DNA synthesis.

40
Q

What is the DNA sliding clamp?

A

protein than encircles DNA and attaches to the rear of DNA polymerase (relative to forward movement)- tethers DNA polymerase to the template strand.

41
Q

Research question: How is the sliding clamp loaded and unloaded onto replicating DNA in humans?

A

The efficnet loading and unloading of sliding clamps by CLAMP LOADERS once DNA poluymerase has disassoicated with DNA is probably important for the overall efficiency of DNA replication.

42
Q

How does a new strand begin?

A

begins with a short stretch of nucleotides: RNA primer synthesized by primate

43
Q

what is RNA primer?

A

A short stretch of RNA nucleotides

44
Q

What synthesized RNA primer?

A

The enzyme primase

45
Q

What happens after primase beings a new strand?

A

IT leaves, DNA polymerase takes over extending the RNA primer with DNA nucleotides as it synthesized the new DNA chain RNA primers are later replaced with DNA later in replication.

46
Q

Which molecule unwinds(separate/ H-bonds broken) DNA strands producing a Y-shaped fork?

A

DNA helicase- uses ATP hydrolysis to finish the job

47
Q

Once separated, what keeps single stranded DNA segments from pairing?

A

SSBS- single stranded binding proteins

48
Q

What does to toposiomerse do?

A

When separating DNA strands, torsional strain is possible with twisting- preventing DNA polymerase from performing,.

Topoisomerase cuts the DNA ahaed of the point where unwinding is taking place- relieving torsional strain

Then rejoins DNA

Mainly circular bacterial chromosome but also in long linear DNA.

49
Q

Helicase does what?

A

Using ATP hydrolysis binding to the ori and unwinding the DNA strand to produce the replication fork

50
Q

Two main criteria of leading strand template

A
  1. Single primer
  2. Synthesized 5’ to 3’ direction towards the fork or direction of DNA unwinding
51
Q

How does replication occur in lagging strand?

A

DNA polymerase happens in the opposite direction of unwinding.

Discontinuous synthesis with a number of primers to keep adding nucleotides from 5’ to 3’ end.

52
Q

Criteria of lagging strands>

A
  1. Multiple primers
  2. Synthesized 5’ to 3’ away from the fork or opposite to the direction of unwinding
53
Q

Why does the leading strand have continuous synthesis?

A

Because it only has one primer and does not break when replicating from 5’ to 3’ end reading Template from 3’ to 5’

54
Q

In the lagging strand, the new DNA strand is synthesized ?

A

in the direction opposite of DNA unwinding require multiple primers on the laggin strand template

55
Q

The discountnous synthesis of DNA in the lagging strand template creates fragments of DNA known as?

A

Okazaki fragments which are 100 to 200 base pairs long.

BIOL 2311 (5 decks)

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