DNA replication

Question 1

Is replication of the DNA double helix liberal, conservative, or semi-conservative?

Answer 1

semi-conservative

Question 2

What is semi-conservative replication?

Answer 2

1. The sequence of bases of
one strand precisely
determines the sequence of
of the other strand. 
2. As DNA is replicated, only
one of the strands of each
daughter DNA double helix
molecule is newly
synthesized.

Question 3

What did the Meselson and Stahl Experiment prove?

Answer 3

semi-conservative replication (Hybrid of light and heavy Nitrogen)

Question 4

How did Meselson and Stahl complete their experiement? (5 steps)

Answer 4

1. Used a CsCl gradient to separate densities of labeled DNA.
2. Used N14 (light) and N15 (heavy) to label DNA strands
3. Initially incubated E. coli in medium containing
   “heavy” nitrogen (15N). This would be the only
   source of nitrogen for the cell. All of the DNA
   would be labeled with 15N.
4. Subsequently, the cells were transferred into a medium containing only “light” nitrogen (14N).
5. Samples were taken, DNA isolated, and separated on a CsCl gradient.

Question 5

Two distinct characteristics of prokaryotic DNA replication

Answer 5

1. Only one site where replication begins (Origin of replication)
2. Circular genome

Question 6

OriC

Answer 6

Origin of Replication for Prokaryotes:

1. 245 base pairs
2. Three A-T rich base pair sites
3. Five DNAa binding sites (recognition)

Question 7

Steps of DNA replication for prokaryotes (6 steps)

Answer 7

1. DNA starts at origin of the replication (OriC)
2. DNAa binds to 5 DNAa binding sites at OriC
3. DNAb (helicase) opens /unwinds DNA double helix at the A-T rich 13 bp sites (requires ATP).
4. SSB (single stranded binding proteins) bind to the single stranded DNA to prevent reformation of DNA double helix.
5. Enzyme Primase (RNA polymerase) synthesizes a 10 BP “starting block/primer,” complimentary to the original DNA template of the strand (primer serves as a “starting block” after the initial split)
6. Topoisomerases to prevent overwinding (uncoils)

Question 8

Type II Topioisomerases

Answer 8

dsDNA uncoiling (cut, unwind, rejoin); Requires ATP

Question 9

Type I Topioisomerases

Answer 9

ssdNA uncoiling (cut, unwind, rejoin)

Question 10

In order to connect a nucleotide , you need a ______ and ______ to form a phosphodiester linkage.

Answer 10

5’ phosphate and 3’ hydroxy

Question 11

What is always added to the 3’ end?

Answer 11

Base

Question 12

What catalyzes DNA replication process?

Answer 12

DNA Polymerases

Question 13

What is a polymerase?

Answer 13

an enzyme that brings about the formation of a particular polymer, especially DNA or RNA.

Question 14

What do DNA replication processes require?

Answer 14

DNTPs, a primer, a template, and Mg2+(cofactor)

Question 15

What direction does DNA replication go in?

Answer 15

Uni-directional, DNA strand synthesis occurs in a 5 prime to 3 prime direction

Question 16

DNA polymerase III

Answer 16

1. Produces 1000 bases per minute
2. Replication: 5 prime to 3 prime direction polymerase function
3. Repair: Backwards, 3 prime to 5 prime exonuclease function

Question 17

How does DNA replication occur?

Answer 17

By synthesizing one continuous strand and one fragmented strand, both in 5 prime to 3 prime direction

Question 18

DNA polymerase I

Answer 18

1. RNA Primer removal from okazaki fragments: 5 prime to 3 prime exonuclease function
2. Uses DNA ligase to “seal/fill” in the spaces/nicks to connect okazaki fragments
3. Replication: 5 prime to 3 prime direction polymerase function
4. Repair: Backwards, 3 prime to 5 prime exonuclease function