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Translation Translation

Translation Translation

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Translation Translation

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  1. Translation Translation • – The Next Step • The next step is for the mRNA to leave the nucleus and move into the cytoplasm to be translated

  2. More on Ribosomes • Ribosomes are made up of two subunits – 60s – large and 40s Small • The two subunits bind to the mRNA much like a clamp – mRNA is between them. • The ribosome moves along the mRNA in the 5’ to 3’ direction adding a new amino acid each time it reads a codon. • The large ribosome unit contains two sites the A site (acceptor) and the P site (peptide)

  3. tRNA – Bob the Builder • This unique clover shaped structure brings the amino acids to the ribosome to the P site where the polypeptide chain is being built.

  4. What it looks like

  5. mRNA – tRNA – Working together • The recognition of mRNA codon by tRNA anticodon • Anticodon – group of three complementary bases that recognizes and pairs with a codon on mRNA

  6. Eg. mRNA UAU the sequence on the anticodon of tRNA is AUA • This means that the a.a. being carried by this tRNA is tyrosine – each tRNA carries one specific amino acid.

  7. How the tRNA move the a.a. • tRNA can exist in two states • – charged – carrying the amino acid - uncharged – lacks amino acid • An enzyme is responsible for adding the appropriate a.a. called aminoacyl – tRNA synthases. • 20 different enzymes for the 20 different amino acids.

  8. tRNA - versatility • They think that because there is more than one codon that tRNA can still bind if 2 of the 3 bases match up - can also be UAC for tyrosine • They call this the wobble hypothesis.

  9. Building the Protein • Three step process • Initiation • Elongation • Termination

  10. Initiation • Ribosome moves along the mRNA, reading the code in triplets – codons. • Translation does not occur until it reads the triplet…..AUG start codon – corresponds to the aa methionine – this means that the initial protein always starts with methionine. • When the start codon is in the P site it delivers the amino acid methionine. tRNA recognizes the codon because of the complimentary anti-codon

  11. Elongation • The second codon is now in the A site – the appropriate tRNA delivers the next amino acid in the sequence. • A peptide bond is formed and the ribosome moves to the next codon. • The first tRNA is released to pick up another a.a. • Again another tRNA moves into the A site to continue building the peptide.

  12. Termination • This continues until the stop codon is read in the A site UAG, UGA, UAA causes the ribosome to stall. • A protein known as a release factor recognizes the stall and causes the ribosomal unit to disassemble releasing the mRNA and the new protein.

  13. Put it together http://www.tvdsb.on.ca/westmin/science/sbioac/genetics/translat.htm

  14. Additional changes • The protein is folded and modified and then targeted to the area of the cell that it is required. • In some cases parts of the polypeptide are cleaved, including the methionine that started the process. • Sugars or phosphates can be added in a process known as glycosylation and phosphorylation. • These modifications occur in the Endoplasmic Reticulum