DNA structure and replication

• DNA (deoxyribonucleic acid)


  The chemical that contains the genetic instructions that make up the blueprint for anything that happens in cells
• Chromosomes


  The structural unit of information in the cell, containing DNA
• DNA from one species can be inserted into the genome of another species and the message can be transcribed and translated
• Prokaryotic cells


  • Relatively unspecialized
  • Have non-membrane bound organelles
• Plasmid


  Small, circular, double-stranded DNA molecule found in prokaryotic cells
• DNA in prokaryotes


  • Located in the region called the nucleoid
  • Circular, not linear
  • Contains genes and proteins, including those that are crucial
• DNA in eukaryotes


  • Located in the membrane-bound organelle called the nucleus
  • Linear, not circular
  • Organised into 46 chromosomes (23 pairs)
  • 22 pairs of autosomes and 1 pair of sex chromosomes (XX or XY)
• Karyotype


  The characteristic chromosome complement of a eukaryotic cell
• Membrane-bound organelles have specific functions in the cell
• This allows DNA from one organism to be expressed in another organism
• DNA Replication
• DNA Replication


  1. Strands are complementary

  2. C pairs with G

  3. Each strand has 5' and 3' ends

  4. Helicase unwinds DNA

  5. Primase creates RNA primer

  6. DNA polymerase adds nucleotides

  7. Leading strand synthesized continuously

  8. Lagging strand synthesized in Okazaki fragments

  9. RNA primers removed

  10. Gaps filled by DNA polymerase

  11. DNA ligase seals fragments
• DNA replication is semi-conservative, each new DNA molecule contains one original and one new strand