DNA: Structure and Function

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DNA Structure and Function
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The DNA Revolution

• 1940s-1960s
• Griffith AveryDNA transformed pneumococcus
  bacteria.
• Encouraged the study of prokaryotic chromosomes.
• Hershey and ChaseBacteriophage experiment. DNA
  from viruses is injected to host bacteria cells.

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Griffith and Avery
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Hershey Chase
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Hershey Chase
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Hershey Chase
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The Search for the Structure of the DNA Molecule

• 1951Rosalind FranklinX-ray crystallography
• ChargaffChargaffs rules. Ratio of nitrogenous
  bases in DNA. Complimentary bases.
• Watson Crick--1953

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Franklin
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Chargaff
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Watson Crick Model of DNA

• Nucleotides
• SugarDeoxyribose
• Phosphate Group
• Nitrogenous Bases
• Adenine Thymine are complementary.
• Cytosine and Guanine are complimentary.

• PurinesAdenine Guanine
• PyrimidinesCytosine Thymine
• 5 EndPhosphate side
• 3 EndOther side

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Watson Crick Model

• DNA is composed of 2 chains of nucleotides that
  form a double helix shape.
• The two strands are antiparallel.
• The backbone of the DNA molecule is composed of
  alternating phosphate groups and sugars.

• The complimentary nitrogenous bases form hydrogen
  bonds between the strands.
• A is complimentary to T and G is complimentary to
  C.

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DNA Model
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DNA

• Functions
• 1. Storage of genetic information
• 2. Self-duplication inheritance.
• 3. Expression of the genetic message.
• DNAs major function is to code for proteins.
• Information is encoded in the order of the
  nitrogenous bases.

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Chromosomes

• Prokaryotic
• Circular
• Very small
• 1 chromosome per cell
• Some enzymes and proteins are associated with the
  DNA.
• Not housed in a nucleus.

• Eukaryotic
• Linear
• Fairly long
• Several chromosomes per cell.
• Histone proteins---spools. Same in all
  eukaryotes
• Housed in a nucleus.
• Nucleosome2 loops of DNA wrapped around 8
  histone proteins.
• Unity theme.

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Central Dogma of Genetics

• DNA
• mRNA
• Proteins
• Traits
• Replication
• Unzip
• Template
• Floating nucleotides

• Template
• Sense strand
• Semiconservative Replication
• DNA Polymerase
• Proofreading functions
• 5 to 3 only
• Replication fork
• Discontinuous assembly
• Okazaki fragments

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RNA

• 3 typesmRNA, tRNA, rRNA
• Ribose
• Uracil replaces Thymine
• Single stranded helix

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Transcription

• RNA polymerase
• Messenger RNA
• mRNA
• Unzipping of DNA helix.
• Sense strand or template strand
• Codons
• Genetic code

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Translation

• Ribosomes
• rRNA
• Large and small subunits
• Codons
• Initiator or start codon
• Methionine (AUG)
• Stop codons
• tRNA

• Initiation
• Chain Elongation
• Peptide bonds
• Chain termination
• Polysome

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