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Protein Synthesis

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					Unit Objectives (Chapter 12-3)
By the end of this unit you will:
 know what transcription is
 know what translation is
 understand how proteins are made.
Transcription
• Transcribing or copying the coded message
  of DNA onto a single stranded nucleic acid
  called mRNA
• DNA’s code is contained in groups of 3
  nitrogen bases called DNA triplets
• One side of DNA is considered the coding
  side, or template, and the other side is
  considered the complimentary side.
• Left side – coding side
• Right side – complimentary strand
 To begin transcription, Helicase causes the
  molecule to split or “unzip”.
 This exposes the nitrogen bases of the
  coding side
 Free floating mRNA nucleotides attach to the
  coding side of DNA
 The whole mRNA strand is removed from the
  coding side of DNA
 The mRNA strand then moves out of the
  nucleus and heads for a ribosome.
 The DNA strand then can re-attach with the
  complementary side of DNA
Transcription




     Transcription and the TATA's
mRNA
   Each group of 3 nitrogen bases of mRNA are
    called codons.
Codon Wheel
Here is how we will “do it”!
 DNA Coding Triplet:
                ATA CGA
 mRNA Codons that would be
  transcribed:
                UAU GCU
 Amino Acids:
            Tyrosine + Alanine
Summary
 Transcription is copying the DNA code onto
  a mRNA molecule.
 mRNA leaves the nucleus and moves to
  the ribosome where the message is
  translated
 AUG is called the “Initiation Codon” . It
  begins the process and always codes for
  Methionine
 “Termination Codons” indicate the end of
  the process. UAG,UAA, and UGA are
  termination codons and don’t code for any
  amino acids
Let’s try Transcription:
 Assume the sequence of nitrogen bases
  below represents the coding side of DNA.
            ACT CCC CGA TAC
 Transcribe the DNA triplets into mRNA
  codons
 Draw the mRNA molecule that would be
  produced during Transcription.
 Translate the mRNA molecule into the
  amino acids it represents. Use your codon
  wheel.
Look like this?
Transcription Review
       DNA contains the genetic code for the production of __________.
       Each group of 3 nitrogen bases in DNA is called a __________.
       The genetic code of _____ is trapped inside the nucleus because
        it is ____________ to fit through the pores in the nuclear
        envelope.
       __________ is the process of copying the genetic code of _____
        onto a single strand of _____.
       The single stranded _____ molecule falls on it’s side with it’s
        nitrogen bases pointing _____ and moves out of the nucleus to
        find a __________.
       Each group of 3 nitrogen bases in mRNA is called a __________.
       AUG is a special codon that is called an ________________. It
        always codes for the amino acid __________.
       Check you codon wheel and identify the amino acids that the
        following codons code for:
         GGC - __________
         UUU - __________
         CAU - __________
         GUA - __________
Transcription Review
   Another special codon found in mRNA stops the
    chain of amino acids and indicates the protein is
    complete. These codons are called
    ________________. There are only 3 of the codons:
    _______; ________ and _______.
   We are always going to assume that the coding side
    of DNA will be the __________ side.
   Opposite the coding side is called the __________
    side.
   Two enzymes play a role in transcription:
    ____________ unzips the DNA molecule and
    __________________ helps attach the free-floating
    mRNA nucleotides to the coding side of DNA.
Transcription Review
   DNA contains the genetic code for the production of Protein.
   Each group of 3 nitrogen bases in DNA is called a DNA triplet.
   The genetic code of DNA is trapped inside the nucleus because it
    is too big to fit through the pores in the nuclear envelope.
   Transcription is the process of copying the genetic code of DNA
    onto a single strand of mRNA.
   The single stranded mRNA molecule falls on it’s side with it’s
    nitrogen bases pointing up and moves out of the nucleus to find a
    ribosome.
   Each group of 3 nitrogen bases in mRNA is called a codon.
   AUG is a special codon that is called an Initiation codon. It always
    codes for the amino acid Methionine.
   Check you codon wheel and identify the amino acids that the
    following codons code for:
       GGC - Glycine
       UUU - Phenylalanine
       CAU - Histidine
       GUA - Valine
Transcription Review
 Another special codon found in mRNA stops the
  chain of amino acids and indicates the protein is
  complete. These codons are called Termination
  codons. There are only 3 of the codons: UGA; UAA
  and UAG.
 We are always going to assume that the coding side
  of DNA will be the left side.
 Opposite the coding side is called the complimentary
  side.
 Two enzymes play a role in transcription: Helicase
  unzips the DNA molecule and RNA polymerase helps
  attach the free-floating mRNA nucleotides to the
  coding side of DNA.
Translation
 The process where the message of
  mRNA is translated into sequences of
  amino acids.
 Translation happens on the surface of
  ribosomes.
 3 codons can fit on the ribosome at one
  time.
 Remember tRNA?
tRNA
        amino acid (specific
        to tRNA)

        tRNA molecule




        nitrogen bases
        called anticodons
tRNA cont…
• Each tRNA molecule with one specific
  anticodon sequence can carry only one
  specific amino acid.
• If the anticodon of tRNA is complimentary
  to the codon of mRNA the amino acid
  carried by that tRNA is dropped off.
• Protein Synthesis PH
• Let’s go back to our mRNA molecule. Draw
  the respective tRNA molecules that would
  be involved in Translation.
Translation Animations
 Translation
 Translation 2
 Translation 3
Activity
   Use your codon chart to complete the
    following table:

Codon         Amino Acid   Anticodon DNA
                                     triplet
AUG
(initiation
codon)
UCC
AAA
CGU
A few things we need to know…
     ← Gene A
     ← Gene B
     •   Exons – translatable segments of a
         chromosome
     •   Introns – segments of DNA that do
         NOT code for proteins
         – Nonsense DNA
     • AUG – intiation codon
     • Codes for methionine
     • UAA, UAG, and UGA are all
       termination codons
Ribosome Structure
                     “A” Site
                     • Arrival Site
                     • First tRNA arrives

                     “P” Site
                     •Peptidyl Site
                     •Amino Acids bond together
        “P”
        Site
                     “E” Site
                     •Exit site
                     •Naked tRNA goes to find
                     another amino acid
Protein Synthesis
Protein Synthesis
   Another look at Protein Synthesis
Quiz: Protein Synthesis
 Assume the strand of DNA nucleotides
  below represents the coding side .
            ACT CCA CGA TAC
 Draw the mRNA molecule that would be
  transcribed.(Value: 4)
 Draw the three tRNA molecules that would
  be complimentary to the mRNA molecule
  you created. Make sure the appropriate
  amino acid and anti-codon are positioned
  on the tRNA drawings. (Value: 3)
 Using you amino acid chart, draw the
  polypeptide that would be created.
  (Value:3)
Mutations
•   Point Mutation: A change in one nitrogen
    base in DNA.
•   EX: DNA              AAA TCT CGA
•      mRNA              UUU AGA GCU
•   Amino Acids          Phen-Arg-Ala
•   Point Mutation
•       DNA                    AAA TGT CGA
•      mRNA                   UUU ACA GCU
•   Amino Acids                Phen-Thre- Ala
``Lucky`` Point Mutation
 DNA     AAA TCT CGA
 mRNA    UUU AGA GCU
 A.A.    Phen-Arg-Ala
 DNA     AAA TCC CGA
 mRNA    UUU AGG GCU
 A.A.    Phen – Arg - Ala
Frame shift Mutations
•   - Mutation that deletes or adds a nitrogen
    base pair.
•   - The result impacts the rest of the amino
    acids in the chain
•   DNA             AAA TCT CGA
•   mRNA            UUU AGA GCU
•   A.A.            Phen – Arg- Ala
•   (Deletion)      AA ATC TCG_
•   mRNA
•   A.A.            YIKES!

				
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posted:4/23/2013
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