Nucleotides

Question 1

explain why new nucleotides can only be added in a 5’ to 3’
direction.

Answer 1

• dna polymerase has a specific active site which is complimentary to the 5’ end

Question 2

Contrast the structures of ATP and a nucleotide found in DNA to give two
differences and similarities

Answer 2

1. both have nitrogenous bases
2. both have a phosphate
3. DNA has a deoxyribose pentode sugar, ATP has a ribose pentose sugar
4. ATP – base always adenine and in DNA
   nucleotide base can be different / varies;
   ATP has 3 phosphate (groups) and DNA
   nucleotide has 1 phosphate (group);

Question 3

Describe the role of two named enzymes in the process of semi-
conservative replication of DNA.

Answer 3

• dna helicase
  dna polymerase

Question 4

Give two features of DNA and explain how each one is important in the
semi-conservative replication of DNA.

Answer 4

• DNA hydrogen bonds are easily broken
  double stranded both strands can act as templates
  -

Question 5

Describe how a phosphodiester bond is formed between two nucleotides
within a DNA molecule.

Answer 5

condensation reaction between deoxyribose pentose sugar catalysed by dna polymerase

Question 6

Name the two scientists who proposed models of the chemical structure of
DNA and of DNA replication.

Answer 6

Watson and crick