Genetic Transcription, Translation,

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Chapter 14

• Genetic Transcription, Translation, Regulation

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Protein Review

• Proteins
• Made of amino acids linked together in a
  polypeptide chain and folded over in a 3-D shape
• Specific order of amino acids determines
  different proteins
• Only 20 amino acids
• Parts of amino acid
• Amino group hydrogen carboxyl group R-group

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How are proteins made?

• Simple
• DNA unwinds and a message is read by mRNA
  (transcription)
• mRNA takes the message to a ribosome
• tRNA reads message and bring the appropriate
  amino acid to the ribosome (translation)
• Amino acids link together to form a protein

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3 types of RNA

• mRNA
• Messenger RNA
• Single stranded chain
• Carries genetic info from nucleus to cytosol
• tRNA
• Transfer RNA
• Single stranded chain near 80 nucleotides
• Hair-pin shaped
• rRNA
• Ribosomal RNA
• Most abundant form
• Globular formation

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Differences between RNA DNA

• DNA
• Deoxyribose
• Double helix
• Contains thymine
• RNA
• Ribose
• Single stranded
• Contain uracil instead of thymine

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Transcription

• mRNA unwinds a portion of the DNA molecule and
  makes a RNA copy called a primary transcript
• Accomplished by RNA polymerase
• Promoter where RNA polymerase binds
• Termination signal stops transcription
• mRNA has to be edited because DNA is not a
  continuous code for amino acids
• Non-coded sections need to be cut out pushing
  coded sections together

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• Introns
• Cut out portions removed
• Exons
• coded portion retained
• Triplets
• 3 bases specify a single amino acid
• Sydney Brenner
• Codon triplet of mRNA bases
• Genetic code resulted from finding the various
  amino acids and triplet codes

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Translation

• Structure of tRNA
• Shaped like a hairpin
• One end links with a specific amino acid
• One end bonds with the codon
• Anticodon sequence of triplet tRNA bases
• Structure of ribosomes
• Composed of 2 subunits (large small)
• rRNA
• When subunits join, 3 binding sites appear (E, P,
  A)
• Free-floating makes proteins that stay in cell
• Attached makes proteins that will leave cell

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Steps of Translation

• mRNA molecule binds to ribosomes small subunit
• start codon is found AUG
• tRNA adds appropriate anticodon
• Large subunit binds and provides the 3 binding
  sites
• tRNA molecule brings corresponding anticodons to
  ribosomes binding sites

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• First anticodon is at P site second anticodon
  binds at A site
• These two amino acids form a peptide bond
• Ribosome shifts down to E site (exit site)
• tRNA molecule has no amino acid attached to it
  and exits the ribosome
• Process continues until stop codon is reached
  UAA UAG UGA
• Polypeptide chain is released forming a protein

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Speed of the Process

• Very fast
• E. coli ? 40 amino acids/second
• Gene segment of DNA that brings about the
  transcription of a segment of RNA
• RNA is made in the nucleus
• rRNA is made in nucleolus
• tRNA mRNA are made from specific segments of DNA

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Genetic Regulation What turns them on and off?

• Jacques Monod Francois Jacob (1950s)
• Lac operon system
• Regulator gene codes for repressor protein
• Promoter site where RNA polymerase binds
• Operator can allow protein to be made or block
  protein from being made
• If a certain substance (inducer) is present, the
  regulator gene does not allow the repressor
  protein to bind to the operator which does allow
  RNA polymerase to bind and the proteins are made
• If a certain substance is not present, the
  regulator genes sends a message to the repressor
  protein which binds to operator site and does not
  allow RNA polymerase to begin making the protein

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Alternate Splicing

• Upon discovery of the human genome
• 30,000 genes
• Humans contain more multifunctional genes genes
  capable of coding for more than one protein
• Figure 14.14 on pg. 277
• 60 of human undergo alternate splicing

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Useful Websites

• http//bhs.smuhsd.org/science-dept/bhsbiology/bhsb
  ioframe.html
• http//www.lewport.wnyric.org/jwanamaker/animation
  s/Protein20Synthesis20-20long.html
• http//www.wisc-online.com/objects/index_tj.asp?ob
  jidAP1302
• http//www.ncc.gmu.edu/dna/ANIMPROT.htm
• http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
  BioBookPROTSYn.html
• http//gslc.genetics.utah.edu/units/basics/transcr
  ibe/
• http//www.wiley.com/legacy/college/boyer/04700037
  90/animations/animations.htm