3.1.5.1 Structure of DNA

• DNA holds genetic information which codes for polypeptides (proteins)
• RNA transfers genetic information from DNA to ribosomes
• The two types of molecules from which a ribosome is made is RNA and proteins
• DNA nucleotides has:

  • Pentose sugar which is deoxyribose
  • The bases: Adenine, Thymine, Guanine and Cytosine
  • Phosphate group
• RNA nucleotides has:

  • Pentose sugar which is ribose
  • The bases: Adenine, Uracil, Guanine and Cytosine
  • Phosphate group
• Nucleotides join together to form polynucleotides through a condensation reaction, removing a molecule of water. This happens between the phosphate group of one nucleotide and the deoxyribose or ribose of another, forming a phosphodiester bond.
• Scientists initially doubted that DNA carried the genetic code because of the relative simplicity of DNA as it's a chemically simple molecule with few components
• • DNA is a polymer of nucleotides making it a polynucleotide
  • Each nucleotide is formed from a deoxyribose sugar, a phosphate group and a nitrogen containing base
  • Phosphodiester bonds join adjacent nucleotides
  • 2 polynucleotide chains held together by hydrogen bonds
  • Between specific complementary base pairs e.g, adenine and thymine and cytosine and guanine
  • Overall forming a double helix
• • The structure of RNA is that it is a polymer of nucleotides making it a polynucleotide
  • Each nucleotide is formed from a ribose, a phosphate group and a nitrogen containing organic base
  • The phosphodiester bonds join adjacent nucleotides
  • Overall forming a single helix
• DNA nucleotide

  • Pentose sugar is deoxyribose
  • Has the base thymine
  • Double stranded or double helix
  • Long as it contains many nucleotides
  • Has hydrogen bonds or base pairing

  RNA nucleotide

  • Pentose sugar is ribose
  • Has the base uracil
  • Single stranded or single helix
  • Shorter as it contains fewer nucleotides
  • It doesn't have hydrogen bonds or base pairing
• The structure of DNA relates to its function by:

  • 2 strands -> both can act as templates for semi-conservative replication
  • Hydrogen bonds between bases are weak -> strands can be seperated for replication
  • Complementary base pairing -> accurate replication
  • Many hydrgen bonds between bases -> Stable and strong molecule
  • Double helix with sugar phosphate backbone -> protects bases and hydrogen bonds
  • Long molecules -> stores lots of genetic information which codes for polypeptides
  • Double helix is coiled -> compact