Understanding DNA Structure and Replication

Oct 30, 2024

DNA Structure and Replication

DNA Structure

  • DNA is a molecule composed of two strands.
  • Strands are twisted in a double helix shape.
  • Comprised of four chemical bases: A, C, G, T.
  • Strands are complementary:
    • T pairs with A
    • C pairs with G
  • Each strand has a 5' end and a 3' end.
  • Strands run in opposite directions.

DNA Replication Process

  1. Separation of Strands
    • Done by the enzyme helicase.
    • Results in a replication fork.
  2. Template Creation
    • Separated strands serve as templates for new DNA.
  3. Initiation by Primase
    • Enzyme primase synthesizes a small piece of RNA called a primer.
    • Primer marks the starting point for new strand construction.
  4. DNA Synthesis by Polymerase
    • DNA polymerase binds to the primer to create the new DNA strand.
    • Can only add bases in the 5' to 3' direction.

Leading and Lagging Strands

  • Leading Strand
    • Synthesized continuously.
    • DNA polymerase adds bases one by one in the 5' to 3' direction.
  • Lagging Strand
    • Synthesized in small chunks called Okazaki fragments.
    • RNA primers are added to start each fragment.
    • DNA polymerase adds bases in the 5' to 3' direction for each fragment.

Finalization of DNA Replication

  1. Removal of RNA Primers
    • Exonuclease removes all RNA primers from both DNA strands.
  2. Filling in Gaps
    • Another DNA polymerase fills in gaps left by removed primers.
  3. Sealing Fragments
    • The enzyme DNA ligase seals all fragments to form a continuous double strand.

Semi-Conservative Nature

  • DNA replication is described as semi-conservative.
  • Each new DNA molecule consists of one old (conserved) strand and one new strand.