Protein Synthesis

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Protein Synthesis

• Using RNA to make proteins

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Going from DNA to Proteins

• Lets review what weve done so far
• We take our DNA and convert it into RNA in a
  process called ________________.
• This happens in the _____________.
• Our proteins are made from Amino Acids so we need
  a bridge to go from the RNA we just made to amino
  acids

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The Genetic Code

• The language of mRNA is called the Genetic Code
  (A, G, U, C) ? (contains only 4 letters)
• It is the matching of the RNA sequence to the
  correct amino acid to make proteins.
• It is based on codons, which are 3 bases together
  on an mRNA chain.
• Each codon codes for a specific amino acid
• There are 64 codons and 20 amino acids so several
  codons will code for the same amino acid
• NOTE The Genetic Code is Universal Most
  organisms follow this code to produce protein
  demonstrating that we are all evolutionary
  related.

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Special Codons Start/Stop Condons

• Start Codon AUG
• Signals the beginning of protein
  synthesis/translation
• Protein synthesis can only begin at this codon.
• Also codes for the Amino Acid Methionine
• Stop Codons UAA, UAG, UGA
• Signals protein synthesis to stop as soon as they
  are reached on the mRNA strand.
• Similar to the period at the end of a sentence or
  the end of a polypeptide chain.

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Genetic Code Square
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Genetic Code Circle
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What do we have after transcription?

• RNA molecules
• mRNA with the DNA code
• tRNA waiting with the amino acid
• rRNA making ribosomes for translation

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How do we get from RNA to Proteins?

• Translation!!
• Changing from the language of nucleic acids to
  the language of proteins in the RIBOSOME
• OR
• process of converting mRNA to amino acids

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All 3 types of RNA are used in protein synthesis
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tRNA and Anticodons

• Amino acids are free floating in the cytosol and
  are transferred to the ribosome by tRNA molecules
• How is tRNA able to do this job? ? it contains 4
  binding sites
• Top part of loop allows for 1 AA to bind
• Bottom part of loop is the anticodon (sequence of
  3 nucleotides) that pairs with its complementary
  matching mRNA
• Ex. If the mRNA UUU then
• anticodon AAA
• Note the pairing of a anticodon with a codon
  ensures that the Amino Acids are being joined in
  the correct order

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Setting the stage for Translation

• Weve made our mRNA and its moving into the
  ribosome
• Our tRNAs are transporting the amino acids over
  to the ribosomes
• OK. We are ready to Translate!

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Steps 1-4 of Translation

• Step 1 Ribosomes attach to the start codon (AUG)
  of the mRNA.
• Step 2 A tRNA with the anticodon of UAC and a
  methionine binds to the mRNA inside the ribosome.
• Step 3 In the 2nd binding site, the next codon
  is read and a tRNA is attached
• Step 4 When the second tRNA attaches, the amino
  acids attached to the 1st tRNA releases from the
  tRNA and binds to the new amino acid with a
  peptide bond

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Steps 5-6 of Translation

• Step 5 Then the 1st tRNA is released and the
  ribosome moves to another codon (3 nucleotides).
• Step 6 When a stop codon is reached, translation
  stops and the ribosome releases the mRNA and the
  created protein.

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Protein synthesis analogy
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Animations

• http//biology.kenyon.edu/slonc/bio3/ribo/ribo3.ht
  ml
• http//www.youtube.com/watch?vNJxobgkPEAo