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DNA Replication

• http//www.johnkyrk.com/DNAreplication.html

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DNA Replication Video
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Nucleic Acids

• DNA and RNA are called nucleic acids.
• A nucleic acid is a huge polymer of either DNA or
  RNA made up of monomers called nucleotides.
• Each nucleotide has three parts
• Sugar Deoxyribose in DNA or Ribose in RNA
• Phosphate group
• Nitrogenous base
• DNAAdenine (A), Thymine (T), Guanine (G),
• Cytosine (C)
• RNAAdenine (A), Uracil (U), Guanine (G),
• Cytosine (C)

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The 4 Nitrogenous Bases

• The four nitrogenous bases are adenine (A),
  guanine (G), cytosine (C) and thymine (T)if DNA
  or Uracil (U)if RNA.

adenine
thymine
Uracil
cytosine
guanine
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Purines

• Adenine and guanine are the larger bases.
• These are called purines.

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Pyrimidines

• Cytosine, thymine and uracil are the smaller
  bases.
• These are called pyrimidines.

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PurinePyrimidine Pairs

• The purine adenine is always paired with the
  pyrimidine thymine in DNA or the Pyrimidine
  Uracil in RNA.
• The purine guanine is always paired with the
  pyrimidine cytosine.
• DNA RNA
• A-T A-U
• G-C G-C

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5 Carbon Sugar

• Deoxyribose and ribose are both 5-carbon sugars.
• We can number the carbons of the deoxyribose
  sugar 1-5.
• The nitrogenous base is bound to Carbon 1.
• The phosphate group is bound to Carbon 5.

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Phosphodiester Bonds

• The Nucleotide monomers are linked together by
  the phosphates.
• These are called phosphodiester bonds
• One phosphate group joins the sugar of Carbon 3
  of one nucleotide monomer to the carbon 5 of the
  other.

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Two Processes of DNA

• You need to understand two processes of DNA.
• Process 1 DNA Replication.
• Each new cell must contain the same DNA as the
  original cell.
• This is how the genetic material is conserved.
• Transcription and Translation
• This is the process of protein synthesis.
• This is how DNA functions in the cell.

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DNA Replication

• Each chromosome is made of two strands of DNA.
• When a parent cell divides into two daughter
  cells, during cell division, each new cell only
  gets one strand of DNA from the parent cell.
• However, every chromosome consists of two DNA
  strands, not one.
• Therefore, the single DNA strand passed from
  parent to daughter cell must have a way to
  replicate itself so that the new cells have two
  DNA strands, not one.

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DNA Replication

• Watson and Crick proposed that one half of the
  DNA ladder serves as a template for making the
  other.
• In 1958 Matthew Meselson and Frank Stahl showed
  that DNA does have a copying mechanism.

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Conserved and Complementary

• When organisms reproduce, one strand of DNA is
  passed unchanged to each of the two daughter
  cells.
• This is known as the conserved strand.
• The second has to be synthesized.
• This DNA strand is called the complementary
  strand.
• This is called semi-conservative replication
  because each daughter cell has one old and one
  newly synthesized DNA strand.

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Anti-Parallel Strands

• The conserved strand is built in the 5 to 3
  direction.
• The complementary strand is anti-parallel and is
  formed in the 3 to 5 direction.
• Therefore each strand is a mirror image of the
  other.
• These strands are joined by the complementary
  basesA with T and G with C.

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DNA Helicase

• DNA replication begins when an enzyme called
  helicase unwinds the two strands of DNA by
  breaking the hydrogen bonds between the
  nitrogenous bases.

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The Leading Strand

• The conserved strand which is the 5 to 3 strand
  is opened at the 3 end.
• The replicating strand now copies the conserved
  strand in the 5 to 3 direction.
• DNA polymerase is an enzyme that adds the
  nucleotides to make the copy.
• This is called the leading strand and is
  synthesized discontinuously.

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The Lagging Strand

• The complementary strand, however, gets opened at
  the 5 end.
• This means that the replicating strand must copy
  it in the 3 to 5 direction.
• DNA polymerase can only add nucleotides in the 5
  to 3 direction.
• The lagging strand must be synthesized
  discontinuously.
• The discontinuous pieces are called Okazaki
  fragments.
• http//highered.mcgrawhill.com/olcweb/cgi/pluginpo
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Citations

• http//porpax.bio.miami.edu/cmallery/150/chemistr
  y/sf3x14a.jpg
• http//www.dnaftb.org/
• http//arbl.cvmbs.colostate.edu/hbooks/genetics/bi
  otech/basics/nastruct.html
• http//www.blc.arizona.edu/Molecular_Graphics/DNA_
  Structure/DNA_Tutorial.HTML
• http//www.bioteach.ubc.ca/TeachingResources/Molec
  ularBiology/DNAReplication.swf
• http//highered.mcgraw-hill.com/olcweb/cgi/pluginp
  op.cgi?itswf535535/sites/dl/free/0072437316
  /120076/micro04.swfDNA20Replication20Fork