18. ANTIPARALLEL ELONGATION

Question 1

1. In which order do DNA Polymerases add nucleotides?

Answer 1

• they add them only in a 5’-3’ direction
• a new DNA strand can only elongate in the 5’-3-‘
  direction
• a nucleotide can never be added to the 5’ end
• a nucleotide can only ever be added to the 3’ end

Question 2

2. Does this diagram of a Replication Fork make sense?

Answer 2

• yes

Question 3

3. What does DNA Polymerase III copy with regards to Leading Strand Synthesis?

Answer 3

• it copies the 3’-5’ strand
• it synthesises a leading strand
• this strand is synthesised continuously in the 5’-3’
  direction
• 2 leading strands are made per bubble

Question 4

4. How many components are seen in this diagram?

Answer 4

• 2 Replication Forks
• 2 Leading Strands
• 2 Lagging Strands

Question 5

5. Does this diagram make sense?

Answer 5

• yes

Question 6

6. What does DNA Polymerase III have to do in order to copy the 5’-3’ strand?

Answer 6

• the DNA Polymerase III must work in the direction
  away from the Replication Fork
• it works in the 5’-3’ direction
• it never works in the 3’-5’ direction

Question 7

7. What happens to the lagging strand?

Answer 7

• it is synthesised discontinuously
• these separate fragments are known as Okazaki
  Fragments
• they are later joined together to form a continuous
  strand
• this is done by DNA ligasw

Question 8

8. Name the 4 Enzymes used during Lagging Strand Synthesis.

Answer 8

1. Primase
2. DNA Polymerase III
3. DNA Polymerase I
4. DNA Ligase

Question 9

9. What is Primase?

Answer 9

• it is an enzyme
• it synthesises the RNA Primers

Question 10

10. What is DNA Polymerase III?

Answer 10

• it synthesises the Okazaki Fragments
• it does this by adding DNA nucleotides to each primer
• this is done in the 5’-3’ direction
• this is the direction that moves away from the
  Replication Fork

Question 11

11. What is DNA Polymerase I?

Answer 11

• it is an enzyme
• it degrades the RNA primers
• it replaces them with DNA nucleotides

Question 12

12. What is DNA Ligase?

Answer 12

• it is an enzyme
• it joins the DNA fragments to the subsequent Okazaki
  Fragments

Question 13

13. Does this Diagram make sense?

Answer 13

• yes

Question 14

14. Does this summary make sense?

Answer 14

• yes

Question 15

15. Does this Summary make sense?

Answer 15

• yes

Question 16

16. What do the limitations of DNA Polymerase create problems for?

Answer 16

• they create problems for the linear DNA of Eukaryotic
  Chromosomes

Question 17

17. What does the Replication Machinery fail to do?

Answer 17

• it fails to provide a way to complete the 5’ ends
• this is a problem for eukaryotic cells
• this is because of their linear chromosomes
• it is not a problem for Prokaryotic cells
• this is because they have circular chromosomes

Question 18

18. What do repeated rounds of replication produce?

Answer 18

• they produce shorter DNA molecules