1.2. Structure and Replication of DNA

Question 1

What is one unit of DNA known as?

Answer 1

A nucleotide.

Question 2

What is a nucleotide made up of?

Answer 2

Deoxyribose sugar, a phosphate and an organic base.

Question 3

What are the four different organic bases in DNA and what are their complementary bases?

Answer 3

Adenine - Thymine

Cytosine - Guanine

Question 4

What holds the leading and lagging strand of DNA together?

Answer 4

Weak hydrogen bonds.

Question 5

What direction do the two strands go compared to each other?

Answer 5

Anti-parallel.

Question 6

What is the twisted coil shape of DNA known as?

Answer 6

A double helix.

Question 7

Describe the process of DNA replication.

Answer 7

The double helix unwinds and the enzyme helicase breaks the hydrogen bonds causing the strands to unzip. A primer (which is a short complementary sequence of nucleotides) is placed on the leading strand. The enzyme DNA polymerase binds to the leading strand and adds free nucleotides to synthesise a complementary strand continuously. On the lagging strand, primers are added one by one and the DNA nucleotides are added to form complementary fragments which the enzyme DNA ligase helps join together.

Question 8

Why do multiple primers need to be present to add nucleotides to the lagging strand?

Answer 8

As nucleotides can only be added from the 5’ - 3’ end.