Nucleic Acids


Nucleotide Structure

Made up of 3 components:

  • Phosphate group
  • Pentose sugar (deoxyribose or ribose)
  • Organic nitrogenous base


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DNA is found in chromatin in nucleus

  • Double stranded polymer 
  • Forms double helix
  • Pentose sugar is deoxyribose

Nucleotides joined together by condensation reactions between phosphate group of one and sugar group of another - forms a sugar phosphate bond known as the sugar phosphate backbone

Strands run anti-parallel to each other (5 prime end and 3 prime end)

DNA is more stable - can survive outside cell


  • Replication
  • Protein synthesis
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  • Single stranded polymer
  • Contains ribose pentose sugar

3 types of RNA

  • mRNA (messenger) - helix structure - carries genetic code from DNA to ribosomes in cytoplasm
  • rRNA (ribosomal) - found in cytoplasm and is a large molecule - forms ribosomes
  • tRNA (transfer) - single stranded molecule - forms a clover leaf structure - cytosine-cytsoine-adenine sequence forms at one end of molecule (anticodon) - transports amino acids to ribosome so they can be synthesised
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There are 5 bases: adenine, guanine, cytosine, thymine, uracil


  • Adenine pairs with thymine - 2 hydrogen bonds
  • Guanine pairs with cytosine - 3 hydrogen bonds


  • Adenine
  • Guanine
  • Cytosine
  • Uracil
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