Year 12 - Nucleic acids, Water and ATP

Question 1

Describe the structure of DNA

Answer 1

• Polymer of nucleotides
• Each nucleotide formed from deoxyribose sugar, a phosphate group and nitrogenous base
• Phosphodiester bonds between adjacent nucleotides
• 2 strands held by hydrogen bonds
• Hydrogen bonds between Adenine and Thymine, Cytosine and Guanine

Question 2

Describe how the structure of DNA relates to its function

Answer 2

• Sugar phosphate backbone provides strength
• Large molecule so can store lots of information
• Helix so compact
• Base sequence codes for amino acids
• Double stranded so strands can act as templates
• Complementary base pairing so accurate replication
• Weak H bonds so easily separated
• Many weak H bonds so strong molecule

Question 3

Describe semi-conservative replication of DNA

Answer 3

• DNA helicase breaks H bonds between the strands
• Each strand acts as a template
• Free DNA nucleotides attach by complementary base pairing with template by H bonds forming
• DNA polymerase joins adjacent nucleotides with phosphodiester bonds in a condensation reaction
• New DNA contains one old strand and one new strand

Question 4

Explain the properties that make water important for organisms

Answer 4

• A metabolite in condensation/hydrolysis reactions
• A solvent allowing transport of substances
• High specific heat capacity so buffers changes in temperature
• Large latent heat of vaporisation so provides cooling effect
• cohesion so supports columns of water
• cohesion so produces surface tension supporting small organisms