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PROTEIN SYNTHESIS: TRANSLATION

PROTEIN SYNTHESIS: TRANSLATION. What is the genetic code?. the sequence of nt in mRNA the order of mRNA n.t . determines the order of amino acids that will bond to build a polypeptide the code is a triplet code: in mRNA, every 3 nucleotides codes for an aa called a CODON .

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PROTEIN SYNTHESIS: TRANSLATION

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  1. PROTEIN SYNTHESIS:TRANSLATION

  2. What is the genetic code? • the sequence of nt in mRNA • the order of mRNA n.t. determines the order of amino acids that will bond to build a polypeptide • the code is a triplet code: in mRNA, every 3 nucleotides codes for an aa • called a CODON

  3. Recall transcription: codon

  4. 64 codons and only 20 corresponding amino acids • The near-universality of the genetic code supports the idea that all organisms are evolutionarily related

  5. All about codons: • Note the chart on p. 207 • several codons code for the same amino acid • codons often differ only by the 3rd nucleotide

  6. START Codon: AUG • also codes for methionine • engages a ribosome to start translating • always found at the beginning of the mRNA transcript but can be found throughout the transcript as well

  7. STOP Codons: UAA, UAG, UGA • cause a ribosome to stop translating • do not code for any amino acids

  8. Translation Basics • Translation = the process of assembling polypeptides from info encoded in mRNA

  9. What’s needed? • mRNA • tRNA • ribosomes

  10. 1. mRNA • mRNA – it has the instructions for protein synthesis from DNA!

  11. 2. tRNA • tRNA - binds specifically to amino acids in the cytoplasm and transports them to the ribosomes • the bottom loop of tRNA has a 3 nt sequence that bonds with mRNA nt • this is the ANTICODON

  12. ANTICODON is complementary to its paired mRNA CODON • Same base pairing rules apply • pairing of anticodon with codon ensures that amino acids are added in the correct order • attachments of amino acid, ATP, and tRNA are all controlled by enzymes

  13. 3. Ribosomes • Composed of • rRNA • Proteins • Found in 2 places: • free in cytoplasm (to produce proteins used by the cell) • attached to ER (to produce exported proteins)

  14. Ribosomes have 3 binding sites that are key to translation 1. mRNA site 2. P site 3. A site • mRNA site- holds mRNA transcript so that its codons are available to bond to tRNA molecules

  15. other 2 sites = P site and A site • each holds a tRNA whose anticodons pair with mRNA codons • P site = holds tRNA with growing polypeptide chain • A site = holds tRNA that is transferring the next amino acid to be added to the chain

  16. Translation • Also called protein synthesis • Synthesis = to put together • 3 steps • Initiation • Elongation • Termination

  17. Protein Assembly1. Initiation • Begins when a ribosome attaches to the start codon (AUG) on a mRNA transcript. • This pairs with UAC on t-RNA. • Remember… AUG codes for methionine • The first amino acid in every polypeptide is initiallymethionine (it can later be removed). Translates in one direction 5’ to 3’!!!

  18. 2. Elongation • As ribosome moves along mRNA transcript, each mRNA codon is paired with its tRNAanticodon. • This causes a specific amino acid to attach to previous amino acid with a covalent bond (called a peptide bond!) • This continues until ribosome reaches a stop codon, ending translation.

  19. Dehydration Synthesis of Proteins

  20. 3. Termination • mRNA is released • the polypeptide is complete.

  21. Result of Protein Synthesis • Polypeptide chain represents the protein’s 1° structure. • As it folds and (or binds) to other polypeptides, it assumes its functional (4°) structure of a completed protein. • What organelle folds and modifies the polypeptide chain into a function protein?

  22. Other info… • Several ribosomes may simultaneously translate the same mRNA transcript = polysomes • usually about 80 nucleotides apart • 1st one starts, gets about 80 nt away from start codon before a 2nd ribosome starts at start codon and follows behind 1st • This speeds up translation of one transcript and results in larger quantities of one particular protein.

  23. https://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter3/animation__how_translation_works.htmlhttps://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter3/animation__how_translation_works.html • http://www.pbslearningmedia.org/asset/lsps07_int_celltrans/ • http://www.wisc-online.com/objects/ViewObject.aspx?ID=AP1302

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