Unit 1 Topic 3 - Replication Of DNA

Question 1

Describe the steps required in DNA replication.

Answer 1

(1) The DNA molecule uncoils
(2) The hydrogen bonds between the bases break
(3) Free Nucleotides become attached to the exposed bases and hydrogen bonds form between the complementary bases.
(4) Sugar-phosphate backbone reforms (covalent bonds)
(5) The DNA recoils
(6) Two identical DNA double helices have been formed.

Question 2

Explain the need for primers in DNA replication.

Answer 2

A Primer is needed as a starting point for replication as DNA Polymerase can only add nucleotides to the 3’ end of a strand that already exists.

Question 3

Describe the replication of the leading strand.

Answer 3

(1) Hydrogen bonds between bases break and the DNA unzips creating a replication fork
(2) A DNA primer (short piece of complementary RNA) attaches to the start of the DNA being copied.
(3) DNA polymerase adds free nucleotides to the 3’ end of the primer (forming sugar-phosphate bonds)
(4) This is a continuous process until the leading strand is fully copied.
(5) The primer is replaced by DNA.

Question 4

Describe the replication of the lagging strand.

Answer 4

(1) The DNA strands separate creating a replication fork
(2) A primer attaches to the start of the DNA being copied.
(3) DNA polymerase moves away from the same fork adding nucleotides to the 3’ end of the primer.
(4) As the DNA unzips, it opens up another section of the lagging strand
(5) A new primer is added
(6) DNA replication is discontinuous creating fragments.
(7) The primers are replaced by DNA
(8) The fragments are joined together by the enzyme Ligase.

Question 5

State that DNA polymerase can only add nucleotides onto the 3’ end of a growing strand.

Question 6

List the 6 requirements for DNA replication.

Answer 6

(1) DNA
(2) Primers
(3) DNA Nucleotides
(4) DNA Polymerase
(5) Ligase
(6) ATP for energy