B2 - Nucleic acids

Question 1

Describe the structure of DNA.

Answer 1

1. Polymer of nucleotides
2. Each nucleotide formed from deoxyribose, a phosphate and an organic/ nitrogenous base.
3. Phosphodiester bonds
4. Double helix/ 2 strands held together by hydrogen bonds
5. Hydrogen bonding between complementary base pairs: adenine and thymine, or cytosine and guanine.

Question 2

Explain 5 properties that make water important for organisms.

Answer 2

1. A metabolite in condensation/hydrolysis/photosynthesis/ respiration
2. A solvent - so metabolic reactions occur OR solvent - so allows for transport of substances
3. High heat capacity - so buffers temperature changes
4. Large latent heat of vaporisation - so provides cooling effect (through evaporation)
5. Cohesion - so supports columns of water in plant xylem
6. Cohesion - so produces surface tension for small aquatic invertebrate to inhabit.

Question 3

ATP is useful in many biological processes. Explain why.

Answer 3

1. Releases energy in small/ manageable amounts
2. Single bond broken releases energy immediately (easily broken down)
3. phosphorylates other substances (making them more reactive)
4. Resynthesises easily (ADP+Pi)

Question 4

Describe and explain how the structure of DNA results in accurate replication.

Answer 4

1. Two strands - so semi-conservative replication is possible
2. Base pairing/ hydrogen bonding holds strands together
3. Hydrogen bonds are weak - so easily broken down (allowing strands to separate)
4. Base pairings act as template - so DNA sequence can be copied
5. A&T, C&G creates a complementary strand
6. DNA template and copy strand of DNA create double stranded DNA.