3.9 DNA replication and genetic code

Question 1

Why do cells divide?

Answer 1

To produce more cells needed for growth and repair of tissues

Question 2

After cell division, what characteristic of the daughter cells makes them identical to the parent cells?

Answer 2

An identical DNA base sequence as that of the parent

Question 3

When a cell prepares to divide, what happens to the cell’s DNA strands?

Answer 3

The 2 DNA strands separate.

Each of these strands acts as a template for the creation of a new double-stranded DNA

Question 4

What rule ensures that the two strands of DNA produced after cell division are identical to the origial?

Answer 4

Complementary base pairing rules

Question 5

Define DNA replication.

Answer 5

The semi-conservative process of the production of two identical DNA molecules

Question 6

Describe and explain the process of semi-conservative replication.

Answer 6

1. DNA’s double helix structure unwinds and separates into two strands. Hydrogen bonds holding the complementary bases must be broken for this to happen.
2. Free DNA nucleotides pair with their complementary bases, visible after the strands separate
3. Hydrogen bonds form between the free DNA nucleotides and their complementary bases
4. The new nucleotides join to their adjacent nucleotides with phosphodiester bonds.
5. Two new molecules of DNA are produced, each with one new strand and one old strand.

Question 7

What type of biological molecule controls DNA replication?

Answer 7

Enzymes

Question 8

What enzyme controls the unwinding of DNA?

Answer 8

DNA helicase

Question 9

How does DNA helicase cause unwinding of the DNA helix?

Answer 9

DNA helicase travels along the DNA backbone, catalysing reactions that break hydrogen bonds between complementary base pairs.
This can be seen as unzipping.

Question 10

What happens with free nucleotides during the process of DNA unwinding?

Answer 10

Free nucleotides pair with newly exposed complementary bases

Question 11

When free nucleotides bind to their complementary bases, which enzyme catalyses what formation?

Answer 11

DNA polymerase - catalyses formation of phosphodiester bonds between nucleotides

Question 12

Describe the simple diagram process of semi-conservative replication.

Answer 12

1. DNA helicase causes DNA helix to unwind

2. After DNA helicase has fully separated the DNA helix