DNA

1
DNA
2
Hammerling Experiment

• Hammerling Experiment
• Cells of green alga cut into pieces and observed
  to see which were able to express heredity
  information.
• Discovered heredity information stored in the
  foot of the cell.

3
Transplantation Experiments

• Very early it was discovered chromosomes are
  composed of proteins and DNA. But it took
  several experiments to conclusively determine
  specifically which substance made up genes.
• Griffith Experiment
• Documented movement of genes from one organism to
  another (transformation).

4
Avery and Hershey-Chase Experiments

• Avery Experiment
• Removed almost all protein from bacteria, and
  found no reduction in transforming activity.
• Hershey-Chase
• Used radioactive isotopes to label DNA and
  protein. Found genes used to specify new
  generations of viruses were made of DNA.

5
Chemical Nature of Nucleic Acids

• DNA made up of nucleic acids.
• Five carbon sugar, phosphate group, and an
  organic base.
• Purines - Large bases
• Adenine and Guanine
• Pyrimidines - Small bases
• Cytosine and Thymine
• Chargaffs Rule
• A T and GC

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Chemical Nature of Nucleic Acids

• Nucleotide made up of a sugar attached to a
  phosphate and a base.
• Nucleotides distinguished by the bases.
• Reaction between phosphate group of one
  nucleotide and hydroxl group of another is
  dehydration synthesis.
• Phosphodiester Bond

7
Three-Dimensional Structure of DNA

• X-ray diffraction suggested DNA had helical shape
  with a diameter of about 2 nanometers.
• Watson and Crick deduced DNA is a double helix
  with bases of two strands pointing inward forming
  base-pairs.
• Purines pairing with pyrimidines.
• Constant 2 nanometer diameter.
• Strands are antiparallel.

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Semi-Conservative Replication

• Each chain in the helix is a complimentary mirror
  image of the other.
• Double helix unzips and undergoes
  semi-conservative replication.
• Each strand of the original duplex becomes one
  strand of another duplex.
• Confirmed by Meselson-Stahl Experiment.

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Replication Process

• Replication of DNA begins at one or more sites on
  the DNA molecule where there is a specific
  sequence of nucleotides called a replication
  origin.
• DNA replicating enzyme DNA polymerase III and
  other enzymes add nucleotides to the growing
  complementary DNA strands.

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Replication Process

• DNA polymerase cannot link the first nucleotides
  in a newly synthesized strand.
• RNA polymerase (primase) constructs an RNA
  primer.
• DNA polymerase adds nucleotides to 3 end.
• Leading strand replicates toward replication
  fork.
• Lagging strand elongates from replication fork.

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Replication Process

• DNA ligase attaches fragment to lagging strand.
• Because synthesis of the leading strand is
  continuous, while the lagging strand is
  discontinuous, the overall replication of DNA is
  referred to as semidiscontinuous.

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Replication Process

• Opening DNA Double Helix
• Initiating replication
• Unwinding duplex
• Stabilizing single strands
• Relieving torque
• Building a Primer
• Assembling Complementary Strands
• Removing the Primer
• Joining Okazaki Fragments

13
Eukaryotic Replication

• In Eukaryotic cells, DNA is packaged in
  nucleosomes within chromosomes.
• Each individual zone replicates as a discrete
  section called a replication unit or a replicon.
• Each replication unit has its own origin of
  replication.
• Fast Replication

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One-Gene/One-Polypeptide Hypothesis

• Genes produce their effects by specifying the
  structure of enzymes.
• Each gene encodes the structure of one enzyme.
• Many enzymes contain multiple polypeptide
  subunits, each encoded by a separate gene.