1.5.1 Structure of DNA

• Describe the basic functions of DNA and RNA in all living cells

  DNA - Holds genetic information which codes for polypeptides (proteins)

  RNA - Transfers genetic information from DNA to ribosomes
• Name the two types of molecule from which a ribosome is made

  RNA and proteins
• Draw and label a DNA nucleotide and an RNA nucleotide


  Picture:

  
• Describe the differences between a DNA nucleotide and an RNA nucleotide

  DNA nucleotide:

  Pentose sugar is deoxyribose

  Base can be thymine

  RNA nucleotide:

  Pentose sugar is ribose

  Base can be uracil
• Describe how nucleotides join together to form polynucleotides

  ● Condensation reactions, removing water molecules

  ● Between phosphate group of one nucleotide and deoxyribose/ribose of another

  ● Forming phosphodiester bonds
• Why did many scientists initially doubt that DNA carried the genetic code?

  The relative simplicity of DNA - chemically simple molecule with few components.
• Describe the structure of DNA

  ● Polymer of nucleotides (polynucleotide)

  ● Each nucleotide formed from deoxyribose, a phosphate group and a

  nitrogen-containing organic base

  ● Phosphodiester bonds join adjacent nucleotides

  ● 2 polynucleotide chains held together by hydrogen bonds

  ● Between specific complementary base pairs - adenine / thymine and

  cytosine / guanine

  ● Double helix

  
• Describe the structure of (messenger) RNA

  ● Polymer of nucleotides (polynucleotide)

  ● Each nucleotide formed from ribose, a phosphate group and a nitrogen-containing organic base

  ● Bases - uracil, adenine, cytosine, guanine

  ● Phosphodiester bonds join adjacent nucleotides

  ● Single helix
• Compare and contrast the structure of DNA and (messenger) RNA

  DNA nucleotide:

  • Pentose sugar is deoxyribose
  • Has the base thymine
  • Double stranded / double helix
  • Long (many nucleotides)
  • Has hydrogen bonds / base pairing

  RNA nucleotide:

  Pentose sugar is ribose

  Has the base uracil

  Single stranded / single helix

  Shorter (fewer nucleotides)

  Does not have hydrogen bonds/base pairing
• Suggest how the structure of DNA relates to its functions

  • ● Two strands → both can act as templates for semi-conservative replication
  • ● Hydrogen bonds between bases are weak → strands can be separated for replication
  • ● Complementary base pairing → accurate replication
  • ● Many hydrogen bonds between bases → stable / strong molecule
  • ● Double helix with sugar phosphate backbone → protects bases / hydrogen bonds
  • ● Long molecule → store lots of genetic information (that codes for polypeptides)
  • ● Double helix (coiled) → compact
• Suggest how you can use incomplete information about the frequency of bases on DNA strands to find the frequency of other bases


  1. % of adenine in strand 1 = % of thymine in strand 2 (and vice versa)
  2. % of guanine in strand 1 = % of cytosine in strand 2 (and vice versa)

  Because of specific complementary base pairing between 2 strands