DNA

• DNA structure:

  • 2-deoxyribose (a pentose sugar)
  • Phosphate ion
  • Nitrogen-containing base (= adenine, cytosine, guanine and thymine)
• A nucleotide is made up from a phosphate ion bonded to 2-deoxyribose which is bonded to one of the four bases: adenine, cytosine, guanine or thymine.
• DNA (Deoxyribonucleic acid)= Contains all the genetic information of living organisms.
• A polynucleotide is multiple nucleotides joined together by a covalent bond between the phosphate on one nucleotide and the sugar of another. This is done through a condensation polymerisation reaction.

  This creates a sugar – phosphate backbone along the chain, where the bases are attached to the sugar.
• DNA exists as two complementary strands arranged in the form of a double helix. The 2 polynucleotides are held together by hydrogen bonds between the bases, A-T and C-G.
• The base pairs always line up in a polynucleotide sequence giving the complementary  strand. 

  • Only adenine has the right atoms in the right place to hydrogen bond with thymine = 2 hydrogen bonds between the pairs. 
  • Only guanine has the right atoms in the right place to hydrogen bonds with cytosine = 3 hydrogen bonds between the pairs. 
• DNA replication:

  The DNA strands (polynucleotides) unwind, free nucleotides align with their base pair on the unwound strand (polynucleotide). A new strand (polynucleotide) forms alongside the original unwound strand producing a new double helix of DNA.