DNA Replication 17-23

Question 1

What do we need for DNA Synthesis?

Answer 1

1. Template (ssDNA)
2. Substrate (A,C,G,T–dNTPs)
3. Machinery (enzymes) DNA Polymerase needs OH group to begin

Question 2

Polymerase moves down template in ____ direction?

Answer 2

3’ –> 5’

Question 3

In Prokaryotes what type of replication is there?

Answer 3

Circular Chromosome - Theta Replication
Plasmids - Rolling Circle Replication

Question 4

What is Theta Replication?

Answer 4

OriC - A/T rich, where it begins
only 1 in ecoli
many in eukaryotes

Question 5

What is the process of Theta Replication in Prokaryotes?

Answer 5

start at oriC, DNA melted to make ss templates
DNA synthesis happens both ways simultaneously.
1 replication bubble made of 2 replication forks
product = 2 circular chromosomes (1 old + 1 new)

Question 6

What is the process Theta Replication in Eukaryotes?

Answer 6

Many replicons (point of origin + area of DNA replicated)
1 bubble (2 forks) from each origin
product = 2 linear chromomes (1 old + 1 new)

Question 7

How do you start DNA Replication?

Answer 7

1. Initiator proteins bind oriC
2. DNA melts at A/T rich regions
3. DNA Helicases bind and continue denaturing
4. SSB (single strand binding) proteins keep DNA melted

Question 8

What is Gyrase?

Answer 8

-Topoisomerase
-Upstream of replication fork
-initiation of replication

Question 9

What is Primase?

Answer 9

-RNA polymerase
-needs no 3’OH group
-makes RNA primer using ssDNA (template)

Question 10

What is RNA Primer?

Answer 10

-short oligonucleotide
-Has 3’OH for DNA polymerase to add onto

Question 11

What is DNA Pol III?

Answer 11

-most of DNA synthesis
-elongates RNA primer
-Very fast
- 3’—> 5’ Exonuclease
—- corrects some mistakes/proofreads

Question 12

What is DNA Pol I?

Answer 12

-removes RNA Primers
- 5’–>3’ exonuclease (destroy RNA primer)
- 5’–>3’ polymerase (replace RNA primer with DNA)
- 3’–>5’ exonuclease (Proofreading)

Question 13

What is Ligase?

Answer 13

Seals final nick in sugar/phosphate backbone

Question 14

What is difference between Prokaryotes and Eukaryotes DNA replication?

Answer 14

Eukaryotes
- many packaging proteins
- Histones
- many replicons/chromosome
- many polymerases
- RLF to control timing (several proteins bind to Oric to mark
- Telomeres (many rounds of repetitive sequences)
—- difficult to replicate end of a lagging strand
—- length is linked to aging and disease

Question 15

What is the problem at the end of linear chromosomes?

Answer 15

Polymerase required primer
polymerase synthesize only 5’ –> 3’

Question 16

What is Telomerase Enzyme?

Answer 16

• extends DNA at chromome ends
  (Protein part) - synthesizes new DNA
  (RNA part) - template for DNA synthesis

Question 17

What are some facts about telomeres/telomerase?

Answer 17

-telomeres contain highly repetitive DNA
-repeat sequence depends on sequence of telomerase RNA
-telomerase expressed in germ and stem cells