Nucleic Acid , Water And ATP

Question 1

Describe the structure of DNA

Answer 1

•Polymer of nucleotides
•Each nucleotide formed from deoxyribose, a phosphate group and a nitrogenous base
•Phosphodiester bonds (between adjacent nucleotides)
•2 strands held by hydrogen bonds
•Hydrogen bonds between adenine,thymine and cytosine,guanine

Question 2

Describe how the structure of DNA relates to its function

Answer 2

•Sugar-phosphate backbone so 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 (Adenine to thymine and cytosine to guanine)
•Weak hydrogen bonds so strands separated easily
•Many weak hydrogen bonds so stable/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 (thymine to adenine and cytosine to guanine) with template by H bonds reforming
•DNA polymerase joins up free adjacent nucleotides with phosphodiester bonds in a condensation reaction
•New DNA molecule 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 so allowing transport of substances
•High specific heat capacity so buffers changes in temperature
•Large latent heat of vaporisation so provides cooling effect
•Cohesion (hydrogen bonding) so supports columns of water
•Cohesion (hydrogen bonding) so produces surface tension supporting small organisms