10.1 Discovery of DNA

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Chapter 10

• 10.1 Discovery of DNA
• 10.2 DNA Structure
• 10.3 DNA Replication
• 10.4 Protein Synthesis

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Griffiths Experiments
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Griffiths Experiments (2)

• 1928
• A mouse injected w/ both heat killed S (virulent)
  and R types can cause pneumonia
• A HEREDITARY FACTOR must be released and taken
  into the R type
• Is this factor protein? DNA? RNA?

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Averys Experiments

• 1940s
• Wanted to determine if the material that was
  transforming was protein, DNA or RNA
• Protease to destroy protein
• Injected w/heat killed S cells and R cells
• Able to transform R to S
• RNase to destroy RNA
• Injected w/heat killed S cells and R cells
• Able to transform R to S
• DNase to destroy DNA
• Injected w/heat killed S cells and R cells
• Not able to transform R to S

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Hershey-Chase Experiment

• 1952
• Protein or DNA?
• Little protein found
• in viruses all the
• DNA was present
• DNA!!!!!

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The Structure of DNA

• Sugar-Phosphate Backbone
• Deoxyribose (sugar found in DNA)
• Nitrogen Bases
• Adenine
• Thymine
• Guanine
• Cytosine

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The Structure of DNA (2)

• Purine
• Double ringed base
• Guanine and Thymine
• Pyrimidine
• Single ringed base
• Cytosine and Adenine
• Purines must pair with pyrimidines so the helix
  can be made (it can twist)

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DNA

• Deoxyribonucleic acid
• Contains genes that code for proteins
• Involved in heredity

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Adenine

• Nitrogen base in both DNA and RNA
• Purine that pairs with thymine in DNA and uracil
  in RNA

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Guanine

• Nitrogen base in both DNA and RNA
• Purine that pairs with cytosine in both DNA and
  RNA

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Thymine

• Nitrogen base in DNA only
• Pyrimidine that pairs with adenine

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Cytosine

• Nitrogen base found in both DNA and RNA

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Deoxyribose

• 5 carbon sugar found in DNA
• Makes up the backbone of DNA (sides of the ladder)

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Phosphate Group

• Backbone of DNA
• Alternates with deoxyribose

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Hydrogen Bonds

• Bond that joins the nitrogen bases together

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Nucleotide

• Building block of nucleic acids
• Contains
• 5 carbon sugar
• Nitrogen base
• Phosphate group

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DNA Carries the Genetic Code
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Replication

• Process of duplicating DNA
• Results in 2 DNA molecules (old and new strands
  mixed)
• Replication is said to be semi-conservative

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DNA Helicase

• Enzyme responsible for the untwisting of DNA
• Starts the replication process

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DNA Polymerase

• Enzyme responsible for attaching the nucleotides
  in the correct order during replication.

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DNA RNA

• Deoxyribose
• Double stranded
• Thymine
• One version

• Ribose
• Single stranded
• Uracil
• 3 versions

Sugar-Phosphate backbone Nucleic Acids Adenine,
Guanine, Cytosine
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Steps in replication

• DNA helicase unwinds the DNA molecule at several
  spots
• Breaks the hydrogen bonds between the bases
• DNA polymerase adds new nucleotides
• 2 new strands
• Original strand new strand semiconservative
  model

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Structure of RNA

• Uracil nitrogen base found only in RNA
  (pyrimidine)
• Ribose 5 carbon sugar found only in RNA

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Types of RNA

• tRNA - transfer
• mRNA - messenger
• rRNA - ribosomal

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tRNA

• Used to carry amino acids to codons on mRNA
• Contains the anticodons on one end and an amino
  acid on the other end

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mRNA

• Contain codons
• Made through transcription in the nucleus
• Read by the tRNA during translation in the
  ctyoplasm

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Transcription Vs. Translation

• Transcription process of making RNA from DNA in
  the nucleus of the cell
• Translation process of making proteins
• tRNA recognizes codons of the mRNA and attaches
  the amino acids in the correct sequence for the
  protein that DNA coded for.

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Codon

• Set of 3 bases found on mRNA
• Complementary to the anticodon on the tRNA

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Anticodon

• Set of 3 bases found on a tRNA molecule
• Recognizes the codon on mRNA during translation

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Amino Acid

• Building block of a protein
• 20 different kinds (essential and nonessential)

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Peptide Bond

• Bond that joins amino acids together in the
  growing polypeptide chain

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Polypeptide

• Made through translation
• Growing chain of amino acids that transforms into
  a protein

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RNA Polymerase

• Enzyme responsible for attaching RNA nucleotides
  in the correct order.

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Steps of Transcription (in the nucleus)

• DNA is the template
• RNA polymerase adds the RNA nucleotides
• Uracil replaces Thymine
• Once transcribed, mRNA leaves the nucleus and
  enters the cytoplasm
• Hooks up with a ribosome to begin translation

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Steps of Translation

• Ribosome, mRNA and tRNA needed to begin
• Anticodon on tRNA matches with the codon on mRNA
• Always begins w/ start codon (AUG)
• Adjacent amino acids form peptide bonds
• tRNA keeps adding amino acids until the stop
  codon is read

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Steps of Translation

• tRNA releases the polypeptide chain (it will fold
  and become a functional protein)
• naked tRNA molecules find more amino acids and
  the process starts all over (as certain proteins
  are needed)

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