2.3 - Nucleic acids

Question 1

Structure of a DNA nucleotide

Answer 1

• one phosphate group
• one nitrogenous base [A,T,G,C]
• both joined to one deoxyribose pentose sugar
• joined with one covalent bond each

Question 2

Structure of RNA nucleotide

Answer 2

• one phosphate group
• one nitrogenous base [A,U,G,C]
• both joined to one ribose pentose sugar
• joined with one covalent bond each

Question 3

Difference between structure of DNA and RNA

Answer 3

• RNA has ribose instead of deoxyribose
• RNA has uracil instead of thymine
• RNA is single stranded rather than double stranded
• RNA is a smaller molecule

Question 4

Structure of a nucleotide chain (e.g. one backbone of DNA)

Answer 4

• 2 nucleotides are joined together with a covalent bond
• between the phosphate group of 1 and the pentose sugar of the other
• The backbone of a nucleic acid is a sugar-phosphate backbone.

Question 5

How two nucleotide chains in DNA are bonded together (e.g. in DNA double helix)

Answer 5

• hydrogen bonds between bases
• complementary base pairing
• purine to pyrimidine
• A to T and G to C
• 2 H bonds between A and T / 3 H bonds between C and G

Question 6

DNA replication

Answer 6

• Double helix untwisted
• DNA unzipped when helicase enzymes break the H bonds between base pairs
• Both strands act as a template for free DNA nucleotides to align and complementary base
  pair [C-G and A-T]
• Hydrogen bonds between the bases reform
• DNA polymerase joins the sugar-phosphate backbones together on the new strands with
  covalent bonds
• The molecules twist back into a double helix
• There are now 2 identical DNA molecules

Question 7

Why DNA replication is known as semi-conservative replication

Answer 7

• This is because 2 identical DNA molecules are made each with 1 strand from the original
  molecule (the conserved strand) which acted as a template strand and 1 new strand