10/13

Question 1

What are the four tasks/obstacles of DNA replication?

Answer 1

Tasks/obstacles:

1) a lot of genetic material/cell
2) lots of cell divisions
3) must be extremely accurate (= fidelity) so as not to accumulate mutations or lose genetic info
4) process must occur rapidly

Question 2

What do the complementary nature of the strands in the double helix suggest?

Answer 2

This suggests that each strand could serve as a template for synthesis of a new complementary/matching strand.

Question 3

Who proposed the semi conservative model of DNA replication?

Answer 3

Watson and Crick

Question 4

Semi conservative model of DNA replication:
1)
2)

Answer 4

1) each parental strand of dbl helix acts as a template to assemble a NEW daughter strand of DNA that is complementary to itself
2) the result of each new molecule of DNA would consist of one parental strand and one new daughter strand
* **parental DNA is semi conserved in new molecule = (1/2)parent and (1/2)new

Question 5

Conservative model of DNA replication:

Answer 5

Original parent. DNA is fully conserved in that the entire molecule of parental DNA serves as a template for entirely new molecule composed of only newly synthesized daughter DNA

Question 6

Dispersive model of DNA replication:

Answer 6

Original double helix is broken down into manageable fragments. Each fragment serves as a template to make new daughter DNA and ends w reassembly of fragments into two complete molecules. (Dispersive pattern of old and new.)

Question 7

____________ and _______ conducted an experiment to determine which replication model was correct.

Answer 7

Messelson and Stahl conducted an experiment to determine which replication model was correct.

Question 8

Messelson and Stahl needed a way to distinguish between old and new DNA. They used:

Answer 8

They used heavy N15 and light N14 isotopes to label the nitrogenous bases of DNA. This allowed them to distinguish DNA by their densities.

Question 9

What three possible arrangements could Messelson and stahl get?

Answer 9

14/14
14/15
15/15 (heaviest)

Question 10

M&S used ______ density gradient to “band” out molecules based on their densities.

Answer 10

M&S used CsCl2 density gradient to “band” out molecules based on their densities.

Question 11

What were the three main steps in the M&S experiment?

Answer 11

1) they grew E. Coli for several generations in the presence of N15 (aka all strands of DNA are marked w N15)
2) switched cells to grow on light N14
3) they analyzed the DNA after one and two rounds of sequential replication

Question 12

What did M&S expect to see if the replication model was semi conservative?

Answer 12

They expected to see half 14/15 molecules and half 15/15 molecules.

Question 13

What did M&S expect to see if the replication model was conservative?

Answer 13

They expected to see 25% 15/15 molecules and 75% 14/14 molecules.

Question 14

What did M&S expect to see if the replication model was dispersive?

Answer 14

They expected to see 100% 14/15 molecules.

Question 15

Results of M&S supported a _________________ model of replication.

Answer 15

Results of M&S supported a semi conservative model of replication.

Question 16

Replicon

Answer 16

Replicon: an individual unit of replication

Question 17

Replication origin

Answer 17

Replication origin: point on a xsome where replication initiates

Question 18

Each replicon contains a ____________ of replication.

Answer 18

Each replicon contains a single origin of replication.

Question 19

Replication bubble

Answer 19

Replication bubble: the unwinding of dbl helix centered over the replication origin

Question 20

Replication fork:

Answer 20

Replication fork: active site of DNA replication as it moves down the molecule

Question 21

Theta replication:

Answer 21

Theta replication: common to circular genomes. EX: bacteria, xsome generates a replication intermediate that resembles Greek letter theta. First described by John Cains

Question 22

Cains experiment (E. Coli):
1)
2)
3)

Answer 22

1) grew bacteria in presence of tritiated-thymidine (radio label for thymine bases)
2) sampled cells at various time points during replication and each sample of cells were lysed open
3) exposed slide to x-Ray film, which gave him a snapshot of the replication process

Question 23

Conclusion of Cains experiment:
1)
2)

Answer 23

1) E. Coli xsome has a single origin of replication
2) DNA unwinds at origin (OriC) and generates localized area of single stranded DNA that can serve as a template to make a new daughter DNA

Question 24

Replication of the E. Coli xsome is ______________.

Answer 24

Replication of the E. Coli xsome is bidirectional.

Question 25

Rolling circle replication:

Answer 25

Rolling circle replication: applies to circular genomes. Unidirectional mode of replication seen in conjugation and replication of phage w circular genomes. This type of replication allows for repeated rounds of replication w/o restarting. It is very efficient for producing lots of copies.

Question 26

Eukaryotic DNA replication:
1)
2)
3)
4)
5)

Answer 26

1) linear DNA template
2) multiple origins of replication
3) bidirectional
4) repli. rate of ~500-1000 nucleotides/min bc of the high level of DNA packaging. Must be unpackaged and then repackaged.
5) multi origins and bidirectional replication help combat slower process so that DNA can be replicated in 3-4hrs of S phase

Question 27

What is the molecular mechanism of DNA replication?

Answer 27

The molecular mechanism of DNA replication is how it’s copied and maintained from one cell division to the next.