2.1.3 Nucleotides and Nucleic acids - DNA replication

Question 1

Explain DNA replication (all processes) [5]

Answer 1

1. The DNA molecule unwinds and hydrogen bonds between the bases are broken causing it to unzip. Using an enzyme called DNA Helicase.
2. There are free nucleotides in the nucleoplasm.
3. The free nucleotides pair up with their complementary base pair on the original strand of DNA.
4. DNA polymerase joins the strong chemical bond between the sugar and the phosphate molecules of adjoining nucleotides on the new strand of DNA.
5. An enzyme rewinds the double helix.
   two new DNA molecules are formed by semi-conservative replication. Each DNA molecule consists of one parent strand and a new strand.

Question 2

Explain the structure of DNA [6]

Answer 2

1. double helix
2. two strands of nucleotides
3. deoxyribose sugar, phosphate and base make up a nucleotide
4. sugar and phosphate joined to form backbones of nucleotides
5. bases: Adenine, Thymine, Cytosine, Guanine
6. Complementary base pairings: A-T, C-G
7. (weak) hydrogen bonding between bases

Question 3

Explain the importance of DNA replication [3]

Answer 3

• identical OR exactly the same DNA/molecules/copies produced
• ensures daughter / new cells have complete / correct / all / the same genetic information / genes / chromosomes.

Question 4

Define semi-conservative replication

Answer 4

through DNA replication two new molecules of DNA are produced. Each one consists of one old strand of DNA and one new strand.

Question 5

What is the purpose/function of the enzyme DNA helicase?

Answer 5

Before replication can occur, the unwinding and separating (unzipping) of the two strands of the DNA double helix is carried out by the enzyme DNA helicase.

Question 6

What is the purpose/function of the enzyme DNA polymerase

Answer 6

DNA polymerase catalyzes the formation of phosphodiester bonds between these nucleotides (after free nucleotides have (complementary base pairings) paired with newly expose bases).

Question 7

Define Mutation

Answer 7

a change in the sequence of bases, due to sequences of bases not being matched exactly or/and an incorrect sequence may occur in the newly-copied strand, which will cause an error.
Errors can occur randomly and spontaneously.

Question 8

Define a codon

Answer 8

it is a sequence of three bases

Question 9

What is known as a code in the base sequence?

Answer 9

a simple triplet code

Question 10

Define Gene

Answer 10

a section of DNA that contains complete sequences of bases (codons) to code for an entire protein.

Question 11

How many different base triplets or codons are there?

Answer 11

64 different base triplets or codons