DNA

• Structure of DNA

  1. DNA is made up of repeating units called nucleotides.

  2. Each nucleotide is composed of a phosphate, a deoxyribose sugar and a base.

  3. The nucleotides are joined by sugar phosphate bonds (forming a sugar phosphate backbone)

  4. There is complimentary base pairing between the four bases:

                 Adenine – Thymine

                 Guanine – Cytosine

  5. Bases are held together by hydrogen bonds

  6. DNA has an antiparallel structure with a deoxyribose sugar at the 3’ end  and phosphate at the 5’

  7. The strands form a double helix.
• Replication

  8. DNA double helix is unwound and hydrogen bonds between bases are broken to form 2 template strands.

  9. DNA polymerase (enzyme) requires a primer, the primer binds to the DNA 3’ end.

  10. DNA polymerase starts to add DNA nucleotides using complementary base pairing to the 3’ end of the new            DNA strand which is forming

  10. DNA polymerase can only add DNA nucleotides in one direction resulting in the leading strand being      replicated continuously and the lagging strand replicated in fragments

  11. The fragments are then joined by another enzyme called ligase.