Biology 102

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Biology 102

• Gene Regulation and Expression
• Part 1

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Lecture Outline

• The relationship of genes and proteins
• Overview From gene to protein
• Transcription

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1. The relationship of genes and proteins

• Review Role of proteins
• Structure
• Skin (collagen) hair and nails (keratin)
  cytoskeleton
• Movement
• Proteins in muscle (actin and myosin)
• Defense
• Antibodies
• Signals
• Several hormones (growth hormone, insulin)
• Receptors for neurotransmitters
• Channels in membranes
• Catalysis
• Enzymes

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How did we learn that genes coded for proteins?

• Beadle and Tatum experiments
• Created mutants of the mold Neurospora
• Different mutants had different nutritional needs
• Deduced which enzymes were missing from each
  mutation, based on nutritional needs

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Beadle and Tatum Experiment
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Beadle and Tatum (cont.)

• Theory One gene, one enzyme
• Later changed to one gene, one protein (or
  polypeptide)
• NOTE They assumed the mutants were all
  single-gene mutants. Didnt know for sure!

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2. Overview From Gene to Protein

• RNA serves several functions in the process of
  building proteins from the DNA blueprint (Fig.
  10-2)
• mRNA
• rRNA
• tRNA

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• RNA differs from DNA
• Single strand
• Different sugar (ribose rather than deoxyribose)
• Uracil replaces Thymine (RNA has no thymine)
• Uracil pairs with Adenine!

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2. Overview From Gene to Protein

• Two major steps from DNA to protein

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2. Overview From Gene to Protein (cont.)

• The genetic code
• Every three bases codes for an amino acid
• Remember that a protein is just a long chain of
  them!
• 64 combinations
• Start and stop sequences also coded
• Redundancy
• Artificial mRNA allowed Francis Crick and
  co-workers to crack the code
• Code is written based on mRNA triplets, called
  codons

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The genetic code (mRNA!)
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3. Focus on first major part Transcription

• Initiation of transcription
• RNA polymerase binds to promotor region on the
  DNA molecule
• Forces local unwinding of the double helix (Fig.
  10-4)

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3. Transcription (cont.)

• Elongation (building the mRNA strand)
• RNA polymerase travels in one direction along
  only one strand--the template strand--of the DNA
• RNA polymerase facilitates pairing of nucleotides
  (complementary base pairing (Fig. 10-4)
• Note free end of mRNA

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Transcription (cont.)

• Termination
• RNA polymerase reaches termnation signal on DNA ?
  mRNA released

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Further modification of RNA

• Introns are cut out, leaving only exons
• What is the function of introns, if they are not
  needed for making the protein?
• Gene can be cut different ways to make different
  proteins
• Mechanism for rapid evolution?