Structure of DNA double helix

What did X-ray diffraction of DNA show

• DNA is helical

• Strands are anti-parallel

Describe the B-form of DNA

• Right-handed double helix

  • Hydrophobic bases = inside

    • Perpendicular

    • 10 bases per turn

  • Hydrophilic backbone = outside

• Complementary base pairs = hydrogen bonds

• 3’-5’ phosphodiester links

Describe other structures of nucleic acids

• A-form DNA = dehydrated DNA

• A-form RNA = double helical

• Z-form DNA = left handed helix

Distinguish between major and minor grooves of DNA

Major = wider + deeper

• Sugar phosphate backbone are close together

• Most proteins bind here

Minor = smaller

1. Sugar phosphate backbone are further apart

What are major and minor grooves of DNA

• Make it easy for bases to be accessed

• Have atoms that can for hydrogen bonds with proteins = can regulate transcription/translation or alter structure

What happens when you heat dna

Desaturation - strand seperates

What happens when you cool down dna

• Cool quickly = strands stay apart

• Cool slowly = strands rejoin

Nucleuses

Cut DNA

Ligase

Join 2 molecules together

Polymerases

Make DNA

Kinases

Add phosphate group

Phosphatases

Re love phosphate groups

Topoisomerases

• Type 1 = single-stranded cuts in DNA

• Type 2 = double strand breaks in DNA