DNA Structure Replication by pgu13428

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									DNA Structure & Replication
         Chapter Ten
• In this section we will be discovering:
• 1. What DNA is
• 2. What components make up the
  DNA strand
• 3. How DNA copies itself
             The Double Helix
• DNA exists as two
  twisted strands joined
  together through the
  hydrogen bonding of
  the nucleotides.
• Its function is to house
  the genetic
  information of an
  organism (in nucleus).
      What Exactly is DNA?
• Composed of monomers known as
  nucleotides (A, T, C & G)
• Often referred to as polynucleotide
• The nucleotides can be arranged in
  any order
• Generating a lot of possible
 Chemical Composition of DNA
• DNA consists of 3 major compounds
  – Deoxyribose sugar
  – Phosphate group
  – Nitrogenous bases
    •   Adenine
    •   Thymine
    •   Cytocine
    •   Guanine
       The Nitrogenous Bases
• Form the center of the
  DNA molecule.
• Nitrogenous bases are
  broken down into two
• 1. Purines: Guanine
  & Adenine
• 2. Pyrimidines:
  Cytocine & Thymine
           DNA Replication
• The process of generating a new DNA
  strand using the parent DNA strand as a
  template. Each new daughter strand will be
  composed of 1/2 of the parent DNA.
• It is made possible because of the
  specificity of the base paring sequences
  (recall Chargaff’s rule).
• This is what happens during S phase of the
  cell cycle.
  The Individual Strands of the
• Each strand has a 3’ and a 5’ end
• Primed numbers refer to the carbon atoms
  of the sugar molecules
• The 3’ carbon has a hydroxyl group
  attached to it. The 5’ carbon has a
  phosphate group attached to it
• Elongation only occurs in the 5’ to 3’
     The Steps to Replication
• 1. The DNA first begins to unzip at specific
  sites along the double helix. These areas
  are known as origins of replication.
• 2. Replication then proceeds in both
  directions creating replication bubbles.
  – Essentially, the parent strands open up as
    daughter strands elongate (lengthen) on both
    sides of each bubble.
    Replication Bubble Rules
• There can be many replication
  bubbles on each DNA chain that is
  being copied
• Eventually all the bubbles merge
  yielding the two completed daughter
  DNA molecules
      More Replication Steps
• 3. DNA Polymerase (an enzyme) adds the
  complimentary bases to the growing
  daughter strands using the parent as a
  template. (this process is called
         Okazaki Fragments
• One of the daughter strands (the lagging
  strand) will be elongated as a series of
  small DNA fragments referred to as
  Okazaki fragments
• DNA ligase (an enzyme) comes in and
  joins the okazaki fragments together
  forming one continuous daughter DNA
Okazaki Fragments
        Replication Accuracy
• DNA replication is incredibly fast and
  accurate thanks to the cooperation of more
  than a dozen enzymes and proteins
• The DNA polymerases actually proof read
  the replication, removing any incorrect
  bases and inserting the correct ones.
• DNA ligase and polymerase can also repair
  damaged DNA.
        What Damages DNA
• UV rays & x-rays
• Ligase and Polymerase can fix these types
  of damage.
     Benefit of DNA Replication
• Ensures that somatic
  cells in an organism
  carry the same
  genetic information
• Is a means by which
  genetic instructions
  are copied for the next
Some DNA Funnies

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