4. Nucleic acids. Secondary and tertiary structure of DNA.

Question 1

Secondary structure on DNA

Answer 1

• 2 DNA chains wounded around each other, creating Double Helix
  -Deoxyribose and phosphate group are on the outside of the helix, facing the aqueous environment, while the bases are directed inwards
• When two chains are paired, major and minor grooves are formed on the surface - proteins are inserted into them.(e.g. a protein regulating transcription in the major groove, so called lambda repressor).

Fig 3

Question 2

Tertiary structure of DNA - supercoiling

Answer 2

Supercoiled DNA, chromatin and chromosomes are the three types of tertiary structures of DNA

Despiralisation during replication or transcription - requires enzymes and energy (ATP).