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Protein Synthesis - Canton Public Schools.ppt

VIEWS: 4 PAGES: 44

									 PROTEIN
SYNTHESIS

   copyright cmassengale   1
DNA
 and
Genes

    copyright cmassengale   2
               DNA
• DNA contains genes,
  sequences of nucleotide
  bases
• These Genes code for
  polypeptides (proteins)
• Proteins are used to build
  cells and do much of the
  work inside cells
       copyright cmassengale   3
  Genes & Proteins
§ Proteins are made of
  amino acids linked
  together by peptide
  bonds
§ Amino acid chains are
  called polypeptides
§ 20 different amino acids
  exist
      copyright cmassengale   4
DNA Begins the Process
  • DNA is found inside the
    nucleus
  • DNA DOES NOT LEAVE THE
    NUCLEUS
  • Proteins by ribosomes
  • Ribosomes may be free in the
    cytosol or attached to the
    surface of rough ER
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 Starting with DNA
• DNA ‘s code must be copied
  and taken to the cytosol
• In the cytoplasm, this code
  must be read so amino acids
  can be assembled to make
  polypeptides (proteins)
• This process is called
  PROTEIN SYNTHESIS
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RNA


      copyright cmassengale   7
 RNA Differs from DNA
• RNA has a sugar ribose
  DNA has a sugar deoxyribose




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      Other Differences
•   RNA contains the
    base uracil (U)
    DNA has thymine
    (T)
•   RNA molecule is
    single-stranded
    DNA is double-
    stranded
          copyright cmassengale   DNA   9
        Three Types of RNA
.


    •   Messenger RNA (mRNA)
    •   Ribosomal RNA (rRNA),
    •   Transfer RNA (tRNA)




               copyright cmassengale   10
   Messenger RNA
• Single stranded chain
  of RNA Nucleotides
• Made in the Nucleus
• Copies DNA & leaves
  through nuclear
  pores
• Contains the
  Nitrogen Bases A, G,
  C, U ( no T )

         copyright cmassengale   11
Messenger RNA (mRNA)
  • Carries the information for a
    specific protein
  • Sequence of 3 bases called
    codon
  • AUG – methionine or start
    codon
  • UAA, UAG, or UGA – stop
    codons

          copyright cmassengale     12
Ribosomal RNA (rRNA)
• Associates with
  proteins to form
  ribosomes
• Site of protein
  Synthesis




            copyright cmassengale   13
Transfer RNA (tRNA)
 • Single stranded molecule with
   attachment site at one end
   for an amino acid
 • Opposite end has three
   nucleotide bases called the
   anticodon


         copyright cmassengale   14
  Transfer RNA
   amino acid
attachment site




                         U A C
                    anticodon
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Transcription
    and
 Translation


  http://www.youtube.com/watch?v=983lhh20rGY
                 copyright cmassengale         16
Pathway to Making a
      Protein
             DNA

           mRNA

  tRNA (ribosomes)

          Protein
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    Protein Synthesis
§ The production of proteins
§ Two phases:
   Transcription & Translation
§ DNA must be copied into
  mRNA
§ DNA DOES NOT LEAVE
  THE NUCLEUS.
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   DNA ® RNA ® Protein
                                               Nuclear
                                       DNA     membrane



             Transcription
                                        Pre-mRNA
Eukaryotic   RNA Processing
   Cell                                 mRNA

                                             Ribosome

             Translation

                                         Protein
               copyright cmassengale                      19
http://www.youtube.com/watch?v=ztPkv7wc3yU

            Transcription
   • The process of copying
     the sequence of one
     strand of DNA, the
     template strand
   • mRNA copies the template
     strand
   • Requires the enzyme RNA
     Polymerase
              copyright cmassengale          20
Template Strand




  copyright cmassengale   21
           Question:
§ What would be the
  complementary RNA strand
  for the following DNA
  sequence?

   DNA 5’-GCGTATG-3’
          copyright cmassengale   22
        Answer:
• DNA 5’-GCGTATG-3’
• RNA 3’-CGCAUAC-5’



      copyright cmassengale   23
      Transcription
• During transcription, RNA
  polymerase binds to DNA and
  separates the DNA strands
• RNA Polymerase then uses
  one strand of DNA as a
  template to assemble
  nucleotides into RNA

       copyright cmassengale   24
RNA Polymerase




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     mRNA Transcript
•mRNA leaves the nucleus
through its pores and goes to
the ribosomes




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       Translation
• Translation is the process
  of decoding the mRNA
  into a polypeptide chain
• tRNA within Ribosomes
  read mRNA three bases
  or 1 codon at a time and
  construct the proteins
       copyright cmassengale   27
  The Genetic Code
• A codon designates an amino
  acid and is found on the
  mRNA
• An amino acid may have more
  than one codon
• There are 20 amino acids,
  but 64 possible codons
• Some codons tell the
  ribosome to stop translating
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     Codons and Anticodons

• The 3 bases of an
  anticodon are
  complementary to
  the 3 bases of a
                                      UGA
  codon
• Example: Codon ACU
                                      ACU
        Anticodon UGA


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Transcription



  Translation




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    Ribosomes
• Site of protein synthesis-
  translation




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   Step 1- Initiation
• mRNA transcript
  start codon AUG
  attaches to the
  Ribosome
  (sandwhiched
  between two
  subunits)

       mRNA transcript
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              Ribosomes

 Large
subunit
            P                 A
           Site              Site


                                     mRNA
           A U G         C U A C U U C G
  Small
 subunit     copyright cmassengale   33
       Step 2 - Elongation
• As ribosome moves, tRNA with their
  amino acids move into position along the
  mRNA
• Peptide bonds join the amino acids




              copyright cmassengale     34
                Initiation
                                               aa2
               aa1




                                             2-tRNA
            1-tRNA
                                             G A U
anticodon   U A C
 hydrogen   A U G        C U A C U U C G A
  bonds      codon                           mRNA
                     copyright cmassengale       35
                Elongation
                     peptide bond
                                                aa3
               aa1                 aa2




                                             3-tRNA

            1-tRNA          2-tRNA           G A A
anticodon   U A C        G A U
 hydrogen   A U G        C U A C U U C G A
 bonds       codon                           mRNA
                     copyright cmassengale       36
                     aa1                  peptide bond
                                                         aa3
                                     aa2


1-tRNA

U A C                                                3-tRNA
(leaves)
                              2-tRNA                 G A A

                           G A U
               A U G       C U A C U U C G A
                                                     mRNA
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           Ribosomes move over one codon
             peptide bonds
    aa1                                       aa4

             aa2                    aa3



                                           4-tRNA

          2-tRNA           3-tRNA          G C U

        G A U G A A
A U G   C U A C U U C G A A C U
                                           mRNA
                   copyright cmassengale       38
                     peptide bonds
             aa1                                 aa4
                    aa2

                                       aa3



2-tRNA
                                              4-tRNA
G A U
(leaves)                      3-tRNA          G C U

                     G A A
   A U G       C U A C U U C G A A C U
                                              mRNA
                      copyright cmassengale       39
           Ribosomes move over one codon
        peptide bonds                          aa5
aa1
      aa2
                                   aa4
               aa3


                                             5-tRNA

                                             U G A
            3-tRNA           4-tRNA

        G A A G C U
G C U A C U U C G A A C U
                                             mRNA
                     copyright cmassengale       40
    aa1           peptide bonds                aa5
            aa2
                   aa3
                                  aa4



                                             5-tRNA

3-tRNA                                       U G A
G A A                        4-tRNA

              G C U
G C U A C U U C G A A C U
                                             mRNA
                     copyright cmassengale       41
         Ribosomes move over one codon
            aa5
      aa4            aa199                    Termination
 aa3 primary                       aa200
     structure
aa2 of a protein


aa1
                                              terminator
                           200-tRNA
                                               or stop
                                               codon
A C U             C A U G U U U A G
 mRNA
                      copyright cmassengale                42
 End Product –The Protein!
      • The end products of protein
        synthesis is a primary structure
        of a protein
      • A sequence of amino acid
        bonded together by peptide
        bonds
                                         aa5
          aa3      aa4
aa2                                            aa199

aa1              copyright cmassengale                 aa200
                                                        43
                             Messenger RNA
                                (mRNA)
          start
                                    http://www.youtube.com/watch?v=D3fOXt4MrOM
          codon

mRNA    A U G G G C U C C A U C G G C G C A U A A

        codon 1      codon 2     codon 3     codon 4      codon 5    codon 6     codon 7

protein methionine    glycine       serine   isoleucine    glycine    alanine     stop
                                                                                  codon



                  Primary structure of a protein
       aa1           aa2           aa3            aa4          aa5              aa6

                                    bonds
                           peptidecopyright cmassengale                               44

								
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