DNA Replication

Question 1

Why does DNA replication occur?

Answer 1

Need a duplicate copy of all DNA prior to mitosis

Question 2

When does DNA replication occur?

Answer 2

S phase of the cell cycle

Question 3

How does DNA replication occur?

Answer 3

• DNA is snipped, which allows DNA helicase to unwind the DNA
• helicase moves along the chromosome creating multiple replication forks
• when the DNA is open, DNA polymerase can make a complimentary strand of DNA
• new bases are added continuously to the leading strand in a 5’ to 3’ direction
• the lagging strand is replicated discontinuously away from the replication fork by the creation of Okazaki fragments
• the Okazaki fragments at later joined together by DNA ligase

Question 4

What does primase do?

Answer 4

Assembles an RNA primer at the origin of replication site

Question 5

What does DNA polymerase do?

Answer 5

Initiates the construction of a complementary strand

Question 6

What do single-stranded binding proteins do?

Answer 6

Stabilises single stranded DNA

Question 7

What does DNA ligase do?

Answer 7

Joins Okazaki fragments together

Question 8

What does the nucleotide replacement enzyme do?

Answer 8

Replaces RNA primers with DNA nucleotides

Question 9

Telomere shortening

Answer 9

No DNA for another priming event

Question 10

What happens in RNA processing?

Answer 10

• capping and polyadenylation

- splicing

Question 11

What is RNA splicing?

Answer 11

Introns are removed and exons joined together, may be in a different order

Question 12

Where does capping occur?

Answer 12

5’ end

Question 13

Where does polyadenylation occur?

Answer 13

3’ end

Question 14

What does capping and polyadenylation do?

Answer 14

Stabilises the mRNA which is relatively unstable