14 Genetic Transcription Translation and Regulation

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					                    Genetic Transcription, 
 Translation, and Regulation
Gene expression
    In order for a cell to carry on its normal business (including division), it must have the
       proper proteins in the proper amounts

    Information to make proteins is stored in DNA
    Genes carry the genetic information to produce a polypeptide

14.1 The Structure of Proteins
    Amino acids are the monomers of proteins
    A string of amino acids is a polypeptide chain
    The polypeptide may be modified or combine with other polypeptides to give a functional
       protein

14.2 Protein Synthesis in Overview
    Transcription and translation
           o     Genes are transcribed to give mRNA copies in the nucleus
           o     mRNA is translated to give the polypeptide on ribosomes in the cytoplasm

14.3 A Closer Look at Transcription
    Transcription
           o     Complementary base pairing occurs between the template DNA strand and the
               new RNA molecule
           o     RNA polymerase is the enzyme
           o     The RNA polymerase recognizes signals present in the DNA sequence (promoter)
           o     This is the site of unwinding of the DNA helix and the initiation of transcription
           o     Since the promoter sequences are near each gene, this allows transcription to
               produce gene-length RNA molecules

    In all eukaryotes, the initial primary transcript is not the finished mRNA
           o     It must undergo RNA processing
           o     One major step in processing is RNA splicing - removal of non-coding introns -
               putting the coding exons together

14.4 A Closer Look at Translation
    Translation takes place on ribosomes and involves three different types of RNA
           o     The mRNA carries the code for a particular amino acid sequence
           o     rRNAs join with ribosomal proteins to give ribosomes
           o     tRNAs are unique adaptor molecules acting as bridges by binding amino acids
               and mRNAs

    During translation, every 3 mRNA nucleotides specifies 1 amino acid
         o     Each 3 nucleotides is a codon
         o     Each tRNA with a particular anticodon will have the same amino acid attached
    Ribosomes are composed of ribosomal proteins and rRNA molecules
          o    Each ribosome is composed of a large and a small subunit
          o    The two subunits come together to initiate translation on a mRNA
    The ribosome has three important sites - A, P, and E
          o    The mRNA moves through the different sites
          o    When the A site is unoccupied, a tRNA with the appropriate anticodon brings the
             next amino acid to add to the chain

    Termination
         o     Occurs when a stop codon is present in the A site
         o     The polypeptide is released
         o     The ribosome splits into its subunits

    Multiple ribosomes can bind to and translate a single mRNA at the same time
          o     This can increase the rate of translation

14.5 Genetic Regulation
   o Gene expression (protein production) is carefully regulated
   o Most genes are not simply “on”, but instead are transcribed when needed

   o Less than 2% of the human genome actually codes for protein
   o What about the other 98%?
          o     Some might be “junk” without any real function
          o     Some may have played a role in generating greater biodiversity
          o     Some are involved in gene regulation

   o What is needed to initiate transcription?
         o     Located within the vicinity of most promoters are enhancers
         o     Transcription factors (proteins) recognize the sequences of the promoters and
             enhancers facilitating the binding of the RNA polymerase

   o Alternative splicing

14.6 Genetics and Life
   o Life depends on the incredible ability of genetic systems to store, use, and pass on
       information

				
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posted:9/29/2012
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