Protein Synthesis: Translation

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Protein Synthesis Translation
Making the Protein from the Code.
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Overview of Translation

• 1) Messenger RNA moves from the nucleus to the
  cytoplasm and attaches to the ribosome.

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• 2) As the ribosome moves along the, mRNA, tRNAs
  with their anticodons (matching the mRNA codons)
  carry the proper amino acids to the ribosomes.
• The first codon is the start
• codon (AUG). The tRNA
• with the anticodon UAC
• carries the amino acid
• methionine.

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• 3) As two amino acids are brought side-by-side,
  they bond by a condensation reaction (dehydration
  synthesis).

Bond
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• 4) The tRNA that held the first amino acid
  leaves.

Bond
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• The ribosome continues to move along the mRNA,
  while a new tRNA brings the next amino acid into
  place.
• 6) This continues
  until the
  stop
  codon is
  
  reached.
• (The protein is
  then processed
  
  for use in, or out
  
  of the cell.)

stop codon
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Translation Animation
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A More Detailed Look at Translation
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Steps in Translation

• Initiation
• Elongation
• Termination

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The Ribosome Binding sites

• There are three
  binding sites on
  the ribosome
• One holds mRNA
  so codons are
  accessible.
• The other two
  hold tRNAs.

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• The binding sites that hold tRNAs are the A
  site and the P site.

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Initiation

• 1) The smaller ribosome unit attaches to the mRNA
  strand (at the methyl guanine MG cap.)
• Many ribosomes may bond to the same mRNA. This
  is called a polysome.)

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• 2) The first tRNA attaches at the start codon.
  Its three-base anticodon matches the mRNA codon.
  At the other end is the attachment point for the
  Amino acid.

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• 3) A transfer RNA with an amino acid is called a
  charged tRNA. (An enzyme and ATP bind to the
  correct amino acid to the transfer RNA molecule.
  At that point it is ready to carry the amino acid
  to its correct place in the growing polypeptide
  chain.)

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• 4) The larger ribosome subunit attaches to the
  smaller one (with the energy from GTP or
  guanosine triphosphate). The Ribosome is complete
  at this point and protein synthesis can proceed.

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Elongation

• 1) The amino acid-charged tRNA that corresponds
  to the next mRNA codon binds to the A site on the
  ribosome.
• 2) A peptide bond forms between two adjacent
  amino acids. (condensation reaction)

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• 3) The ribosome moves along the mRNA and the
  process continues. The previous tRNA leaves.
• The ribosome moves along so that the next tRNA
  has now moved from the A to the P site. Another
  charges tRNA brings an amino acid to the growing
  protein chain.

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Termination

• 1) Elongation continues until
  the stop codon is
  reached.
• 2) A special protein binds to
  the stop codon
  at the A site.
• 3) The newly-formed polypeptide is released. The
  tRNAs are released. The two ribosome subunits
  separate.

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Translation Animation
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Translation Animation
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Where do the Proteins Go?

• Proteins formed at the ribosomes, free in the
  cytosol, are used within the cell.
• Proteins formed at the R.E.R. (rough endoplasmic
  reticulum) are transported out of the cell.

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Transport and Modification

• The first few amino acids provide the direction
  that proteins will travel within the cell. It is
  known as the signal sequence.
• The polypeptide chain may be modified so that it
  can function properly. It may be cut into smaller
  segments, or a portion may be removed with
  special enzymes.