D1.1 DNA Replication

Cards (26)

  • DNA stands for deoxyribonucleic acid
  • DNA contains the genetic information for the development and growth of cells and multicellular organisms
  • DNA replication is the production of identical copies of DNA (the new copies will have an identical nucleotide sequence to each other and the original DNA molecule)
  • in eukaryotic cells, DNA replication occurs before mitosis (required for growth and tissue replacement in multicellular organisms) and meiosis (required for reproduction)
  • enzymes are involved in the process of DNA replication i.e. helicase and DNA polymerase
  • Helicase, an enzyme involved in DNA replication, unwinds the DNA double helix by breaking the hydrogen bonds between complementary nucleotides (the two separate strands will act as templates for the new strands of DNA)
  • the complementary base pairs are:
    adenine to thymine
    guanine to cytosine
  • DNA polymerase moves along each strand of DNA (after helicase unwinds them) linking nucleotides together to form a new chain using the pre-existing strands as a template
  • the complementary bases are held together by hydrogen bonds
  • DNA replication is a semi-conservative process (new DNA molecules have on parents strand and one newly synthesized strand)
  • why is DNA highly accurate?
    because of the complementary base pairings and it's semi-conservative
  • the polymerase chain reaction (PCR) is a method for amplifying copies of a DNA sequence from a small sample
  • polymerase chain reactions work by using cycles of heating and cooling
  • Process of PCR
    Denaturation - DNA is heated to 95C to break down hydrogen bonds and separate the two DNA strands
    Annealing - temperature is reduced to 54C allowing DNA primers to bind to both strands of DNA
    Temperature is increased to 72C which allows Taq DNA polymerase to replicate both strands.
  • Taq DNA polymerase is obtained from bacterium (thermus aquaticus) which is adapted to living in hot springs so the enzyme does not denature during PCR
  • Gel electrophoresis is a technique used to separate charged molecules like DNA or proteins
  • gel electrophoresis is used to create DNA profiles or DNA fingerprints
  • DNA is an acid and dissociates to become negatively charged in water
  • a DNA profile is a unique pattern created from an individuals DNA fragments (they are used in forensic science and paternity testing)
  • enzymes involved in DNA replication:
    DNA primase
    DNA polymerase I
    DNA polymerase II
    DNA ligase
  • in deoxyribose carbons are numbered, carbon-1 (1') is the first carbon moving clockwise from an oxygen atom etc,
  • in a nucleotide:
    nitrogen base bonds to C-1' (carbon 1)
    phosphate bonds to C-5' (carbon 5)
  • a DNA molecule has two antiparallel strands of DNA. one strands runs from 5' to 3' and the other from 3' to 5'
  • DNA polymerase is continuous on the leading strand moving towards the replication fork
  • DNA replication is discontinuous on the lagging strand moving away from the replication fork, producing Okazaki fragments
  • errors are extremely rare in complementary base pairings but they do occur sometimes. DNA polymerase III proofreads the growing DNA chain and removes any mismatched bases at the 3' end, replacing them with correct nucleotides