DNA

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DNA
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DNA History

• Griffith Experimented on mice and observed some
  harmless strains of bacteria could change into
  harmful strains. He called this transformation.
• Avery Discovered that DNA is the nucleic acid
  that stores and transmits the genetic information
  from one generation to the next.

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Griffith
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More DNA History

• Hershey-Chase Concluded that the genetic
  material in bacteria was DNA not proteins
• Watson Crick created the double helix model
  for DNA.

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Hershey Chase
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Watson Crick
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Understanding DNA
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The Importance of DNA
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Structure of DNA

• DNA is a long molecule made up of units called
  nucleotides.
• Each nucleotide is made up of three parts a
  5-carbon sugar called dioxyribose, a phosphate
  group, and a nitorgenous base (Nitrogen
  Containing).
• The backbone of DNA is formed by sugar and
  phosphate groups of the nucleotide.
• The nitrogenous base stick out from the sides and
  can be joined together in any order, meaning that
  any sequence of bases is possible.

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DNA Subunits
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Nitrogenous Bases

• There are four kinds of nitrogenous bases.
• They are divided into two classes purines and
  pyrmidines
• Purines Adenine and Guanine
• Pyrmidines Cytosine and Thymine

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Chargaffs Rules

• Chargaff discovered how the nitrogenous bases
  bond together.
• He discovered that Adenine always bonds with
  Thymine and that Cytosine always bonds with
  Guanine.

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Chargaff
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The Genetic Code
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Prokaryotes DNA

• In prokaryotes, DNA molecules are located in the
  cytoplasm of the cell.
• Most prokaryotic DNA is a single circular
  molecule that contains nearly all the cells
  genetic information.

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Eukaryotes DNA

• Many eukaryotes have 1000 times as much DNA as
  prokaryotes.
• DNA is located in the nucleus in the form of
  chromosomes.
• Chromosomes are DNA wound tightly around proteins
  called histones.

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DNA Length

• E. Coli have about 4,639,221 base pairs. It is
  about 1.6mm in length. This sounds small until
  you realize the bacteria is only 1.6µm in
  diameter.
• Thus DNA must be wrapped tightly to fit into
  cells. Imagine fitting 900 yards (300m) of rope
  into a backpack.

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DNA Replication

• During DNA replication, the DNA molecule
  separates into two strands, then produces two new
  complimentary strands following the rules of base
  pairing (Chargaff Rules). Each strand of double
  helix of DNA serves as a template, or model, for
  the new strand.

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How It Occurs

• DNA replication is carried out by a series of
  enzymes.
• The enzymes unzip the DNA molecule creating two
  strands that serve as templates.
• Complimentary bases are added to the strands, for
  example a strand of DNA with the bases ATTCGAG
  would have a complimentary strand of TAAGCTC.

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Replication Continued

• Each new DNA molecule has one new stand and one
  strand from the original molecule.
• The enzyme DNA polymerase, the principal enzyme,
  proofreads the new DNA strands, helping to
  maximize the odds that each molecule is a perfect
  copy of the original.

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Replication of DNA