Lecture 12: DNA replication

Question 1

Why does telomere shortening occur?

Answer 1

• DNA lost from lagging strand at 5’ end
• last RNA primer on lagging strand is removed but cannot be replaced

Question 2

Which enzyme extends telomeres?

Answer 2

telomerase

Question 3

Where is telomerase active?

Answer 3

germ cells and very few somatic cells

Question 4

What are the DNA Polymerase enzymes in bacteria and what is their basic function?

Answer 4

• Pol I - helps remove RNA primer and replaces with DNA in chromosome replication, also has a major role in repair of damaged DNA
• Pol II - restarting replication when blocked by damaged DNA, also a role in DNA repair
• Pol III - Chromosome replication
• Pol IV and V - allow replication to bypass some types of DNA damage, also involved in DNA repair

Question 5

Regarding DNA Pol I:
1) Which gene is it linked to?
2) Is it a 5’-3’ polymerase?
3) Is it a 3’-5’ exonuclease?
4) Is it a 5’-3’ exonuclease
5) What is its polymerisation rate?

Answer 5

1) polA
2) yes
3) yes
4) yes
5) 16-20 nucleotides per second

Question 6

Regarding DNA Pol III:
1) Which gene is it linked to?
2) Is it a 5’-3’ polymerase?
3) Is it a 3’-5’ exonuclease?
4) Is it a 5’-3’ exonuclease
5) What is its polymerisation rate?

Answer 6

1) polC
2) yes
3) yes
4) no
5) 250-1000

Question 7

What is the function of a 3’-5’ exonuclease?

Answer 7

• involved in proofreading (ie. checks the nucleotide previously inserted)
• degrades from 3’ end

Question 8

What is the function of a 5’-3’ exonuclease?

Answer 8

• degrades RNA primers at the end of Okazaki fragments

Question 9

What is the role of helicase?

Answer 9

unwinds DNA duplex to produce the replication fork

Question 10

Which gene makes helicase in E. coli?

Answer 10

DnaB

Question 11

What is the role of the primosome?

Answer 11

makes the RNA primer, moving with the lagging strand

Question 12

Which gene makes the primososme in E. coli?

Answer 12

DnaC, DnaG and others