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Translation and the Genetic Code

Translation and the Genetic Code. Review:. DNA codes for_______________  PROTEINS! Proteins = chains of_________=________  Amino Acids  Polypeptides 20 Different Amino Acids!.

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Translation and the Genetic Code

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  1. Translation and the Genetic Code

  2. Review: • DNA codes for_______________ PROTEINS! • Proteins = chains of_________=________ Amino Acids Polypeptides • 20 Different Amino Acids!

  3. But...Can a particular order of Nitrogenous bases in DNA & RNA be translated into a particular order of amino acids in a polypeptide?

  4. YES! With the GENETIC CODE! • Language = mRNA • Letters = A, U, C, G • Words = codons = 3 bases long

  5. Codon • 3 consecutive nucleotides on mRNA that specify a single amino acid to be added to the polypeptide • 64 possible codons

  6. The Genetic Code

  7. Special Codons: • AUG = Start (methionine) • UGA, UAA, UAG = Stop (no amino acid) • TO USE THE GENETIC WHEEL, START AT THE MIDDLE OF THE WHEEL, AND THEN WORK YOUR WAY OUTWARDS!

  8. Practice: • Using the strand of mRNA below AND the genetic code wheel, determine the codons and their corresponding amino acids. AUG UCC GAU GGC UAC GUU CCC UAA

  9. So, we know that the sequence of nucleotide bases in mRNA serves as instructions for the order of amino acids in the construction of proteins, but… how does the protein get “put together”?

  10. Translation! • decoding of mRNA message into a polypeptide chain • takes place on ribosomes in cytoplasm • also called protein synthesis

  11. Process of Translation: • Before translation, mRNA is transcribed from DNA in the nucleus, then released into cytoplasm. • mRNA then attaches to a ribosome in the cytoplasm. • mRNA moves through ribosome. As it moves, the proper amino acid (the one that matches the codon) is brought to the ribosome by the tRNA.

  12. Messenger RNA Messenger RNA is transcribed in the nucleus. Nucleus Lysine Phenylalanine tRNA Methionine Transfer RNA The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. Ribosome Start codon mRNA

  13. Notes: • Translation always starts at AUG codon. • Each tRNA molecule carries one type of amino acid and has three unpaired bases that are complementary to one mRNA codon. • tRNA bases = anticodon

  14. Process of Translation (Continued): • Ribosome forms peptide bonds between amino acids, then breaks the bond between tRNA and amino acid so tRNA is released. • The ribosome moves down mRNA strand, matching tRNA anticodons to mRNA codons. • Translation continues (polypeptide gets bigger) until ribosome reaches STOP codon on mRNA.

  15. The Polypeptide “Assembly Line” The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids. Growing polypeptide chain Ribosome tRNA Lysine tRNA mRNA Completing the Polypeptide The process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain. Translation direction Ribosome

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