Nucleic acids + water

Question 1

Bond joining sugar + phosphate group in a nucleotide

Answer 1

Phosphodiester bond

Question 2

Chargaff’s rule

Answer 2

Adenine pairs w/ Thymine (2 H bonds)
Guanine pairs w/ Cytosine (3 H bonds)

Question 3

Structure of DNA

Answer 3

Two polynucleotide strands which run anti-parallel (5’-3’, 3’-5’) and twist together to form double helix. Hydrogen bonds form between the complimentary base pairs. Contains deoxyribose, N containing organic base + phosphate group

Question 4

Structure of RNA

Answer 4

Single, helical polynucleotide chain which contains organic bases: adenine, uracil, guanine and cytosine. Contains ribose.

Question 5

Structure of DNA related to its function [6]

Answer 5

• double stranded w/ sugar phosphate backbone -> bases + H bonds are protected
• large -> can store a lot of information
• helix makes it compact -> efficient storage of genetic info
• base sequence codes for amino acids -> function of genetic code
• double stranded + H bonds makes it strong but can be separated -> DNA replication

Question 6

Steps of DNA replication

Answer 6

• DNA helicase breaks H bonds -> helix separates + unwinds
• exposed strand acts as template on which complimentary free nucleotides bind by specific base pairing
• nucleotides join by condens. reaction w/ DNA polymerase (phosphodiester bonds) -> 2 identical DNA molecules

Question 7

Semi-conservative replication

Answer 7

Each new DNA molecule after one generation contains one of the original strands and one new strand.

Question 8

What does ATP consist of?

Answer 8

adenine, ribose , 3 phosphate groups joined by unstable bonds

Question 9

Why is ATP a better immediate energy source than glucose?

Answer 9

• releases less energy per molecule -> more manageable amounts than glucose
• hydrolysis of ATP to ADP is a single reaction but glucose requires series of reactions -> released quickly

Question 10

Uses of ATP

Answer 10

• metabolic processes
• movement
• active transport
• secretion
• activation of molecules

Question 11

Significance of high latent heat of vaporisation in water

Answer 11

• high incidence of H bonding makes evaporation difficult
• when bonds break much energy is released
• evaporation (sweating) is an efficient cooling mechanism

Question 12

Significance of transparency in water

Answer 12

allows aquatic plants to photosynthesise

Question 13

Significance of high specific heat capacity in water

Answer 13

water within aquatic envs. + cells is slow to freeze providing stable environment

Question 14

Significance of strong cohesion of water

Answer 14

Supports columns of water enabling effective transport
Surface tension of water-air boundary is high