An Introduction to Protein Synthesis

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An Introduction to Protein Synthesis
Biology 12 Cole Harbour District High
School Wednesday, March 21st, 2007
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George Beadle Edward Tatum

• "one gene, one enzyme hypothesis states that
  that a single gene controls the production,
  specificity, and activity of each enzyme in a
  metabolic pathway. Thus, mutation of such a gene
  changes the ability of the cell to carry out a
  particular reaction and disrupts the entire
  pathway.

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Revised

• "one gene one polypeptide hypothesis"  A revision
  of the one gene, one enzyme hypothesis. Some
  proteins are composed of different polypeptide
  chains encoded by separate genes, so the
  hypothesis now holds that mutation in a gene
  encoding a specific polypeptide can alter the
  ability of the encoded protein to function and
  thus produce an altered phenotype.

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RNA Production

• RNA occurs in the nucleus as well as in the
  cytoplasm (also remember that it occurs as part
  of the ribosomes that line the rough endoplasmic
  reticulum).
• Scientists for some time had suspected such a
  link between DNA and proteins.

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Protein Synthesis at a glance
This is what we did in the DNA lab!
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Differences between DNA and RNA
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The Delivery Route

• Messenger RNA (mRNA) is the blueprint for
  construction of a protein.
• Ribosomal RNA (rRNA) is the construction site
  where the protein is made.
• Transfer RNA (tRNA) is the truck delivering the
  proper amino acid to the site at the right time.

tRNA
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Starting Protein Synthesis

• DNA controls all the cell activities largely by
  controlling the production of thousands of
  proteins many of which are specific to each
  cell.
• Protein synthesis begins when the DNA unzips
  nucleotides of mRNA (messenger RNA) find their
  complementary base and join into a chain. A pairs
  with U and G pairs with C

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TRANSCRIPTION

• Once the chain is fused, the mRNA moves away from
  the parent DNA strand which then rejoins.
• This completes the process of transcription (the
  message of the DNA has been TRANSCRIBED into the
  mRNA.
• The mRNA now leaves the nucleus and goes out to a
  ribosome.

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Word Bird

• Transcription to transcribe means to translate
  or to copy.
• When DNA directs the duplication of another
  nucleic acid called RNA, the process is called
  transcription. Transcription is making an RNA
  copy of a DNA sequence. It is the first stage in
  Protein Synthesis! (Thanks
  Webster's!)

TRANSCRIPTION
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The Language of Genetics

• Nucleotides are arranged in a linear sequence,
  some are several thousands long.
• A single base dose not contain a code.
• Westandonguardforthee

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Reading the DNA code

• Rather three bases or TRIPLETS carry the code.
  Like a book that contains only three nucleotides
  (triplets).
• From the 4 bases (A, U, C, G) there are 64
  possibilities for triplet formation.
• These three letter codes determine the exact
  order in which amino acids will be arranged in a
  specific protein molecule.

Books containing Triplets!
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UNZIPPING DNA

• RNA polymerase (an enzyme) opens the part of the
  DNA to be transcribed.
• Only one strand of DNA (called the template
  strand) is transcribed.
• RNA nucleotides are available in the region of
  the chromatin and are linked together similar to
  the DNA process.

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Unzipping DNA
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Codons

• After RNA is transcribed it detaches itself and
  may be stored for a short time in the nucleolus
  or move immediately through the nuclear pores
  into the cytoplasm.
• The RNA has the code for specific amino acids.
• This type of RNA is called mRNA.
• Like DNA there are 64 combinations of codons in
  mRNA.

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mRNA in the Cytoplasm

• mRNA acts as the template for the assembly of
  amino acids and the production of protein
  molecules.
• mRNA gt amino acid combinations gt Translation.

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Word Bird

• Translation To change from one language to
  another.
• So here we have mRNA being read and patterned
  into amino acid sequences which combine together
  to make new proteins.
• Ribosomes help read the mRNA to determine which
  amino acids are selected.
• (Thanks again Webster's!)

TRANSLATION!
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Amino Acid trains

• Throughout the cytoplasm we find amino acids.
• The sequence which they join together during
  synthesis is determined by the mRNA codons.
• The amino acids are picked up and brought to the
  template using tRNA.

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Anticodon

• The tRNA carries the amino acids to the mRNA
  using coding that is the exact opposite of the
  code found on the mRNA known as an anticodon.
• The anticodon tells the specific amino acid to
  come to the mRNA.
• After the tRNA delivers the amino acid it moves
  to the cytoplasm.

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• Upon completion of the chain, the protein is
  released and passes into the cytoplasm where it
  is used.

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Protein Synthesis Summary
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Seat Work Due at the Start of the next class.

• 10 Vocabulary words

READINGS page 636-639 Questions 2-7 page 639