DNA Replication

• DNA Replication


  The biological process of producing two identical replicas of DNA from one original DNA molecule
• Steps in DNA Replication

  1. Initiation

  2. Unwinding of DNA

  3. RNA Primer Binding

  4. Elongation

  5. Ligation

  6. Termination
• Initiation


  • The DNA is separated

  The RNA primase lays an initiator (primer)
• Components Needed in Initiation

  • Helicase
  • Topoisomerase
  • SSB Proteins
  • RNA Primase
• Helicase


  Enzyme that unwinds the "mother" DNA, breaking the DNA's hydrogen bonds
• Topoisomerase


  Enzyme that helps the Helicase by preventing the DNA from supercoiling
• SSB Proteins


  Proteins that maintain the DNA separated
• RNA Primase


  Enzyme that plants the primer as an initiation point
• Replication Fork


  The separated DNA strand that shall be used in DNA replication, maintained by the SSB proteins
• RNA Primer Binding


  The RNA primase binds or lays the PRIMER for elongation
• Directionality of DNA Strands

  • The upper strand has 5' → 3' directionality

  The lower strand has 3' → 5' directionality
• Elongation


  The DNA polymerase distributes the new bases

  The birth of the leading and lagging strand
• Primer


  The starting area of DNA Polymerase in distributing DNA new bases
• DNA Polymerase


  Enzyme that distributes the new DNA bases
• Leading Strand


  The directing strand with 5' to 3' directionality
• Lagging Strand


  Strand with Okazaki Fragments (3' to 5' directionality)
• Nitrogenous Bases


  • Thymine
  • Adenine
  • Guanine
  • Cytosine
• Okazaki Fragments


  DNA segments found only in lagging strands used in replicating
• Ligase


  Enzyme that seals the gaps between Okazaki Fragments
• Leading Strand


  • The DNA polymerase elongates the strands in the 5' to 3' direction

  The DNA polymerase starts distributing new bases going RIGHT

  It will end if it reaches the last base found at the upper strand's 5'
• Lagging Strand


  • The DNA polymerase follows the 3' to 5' direction

  The DNA polymerase starts distributing new bases going LEFT

  The DNA polymerase will delay and stop at a certain segment due to its direction

  Another RNA primase must lay another RNA primer to resume the elongation process

  Another DNA polymerase shall be distributed again for the next DNA segment

  Each DNA segment produced is called an Okazaki Fragment

  The ligase enzyme shall seal the gaps between the Okazaki fragments
• Ligation


  The ligase shall seal the new strands
• Termination


  The ending point is reached and two baby DNAs are born
• Characteristics of DNA in Replication

  • Anti-Parallel - the DNA follows the opposite prime directionality

  Semi-conservative - each helix that is created contains one strand from the helix from which it was copied

  Semi-discontinuous - the DNA is semi discontinuous due to the lagging strand's discontinuous nature
• Chargaff Rule


  Adenine (A) → Thymine (T)

  Guanine (G) → Cytosine (C)
• DNA Start Codon


  TAC is the fixed starting codon of a replicated DNA
• DNA Stop Codon


  ATT, ATC, ACT are the fixed ending codons that shall be converted to an RNA stop codon