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The Genetic Code

The Genetic Code. Gene -a section of DNA that codes for an amino acid sequence (on RNA), which is a building block for proteins. There are 20 different amino acids made up of three letter words (four letters to choose from-nitrogenous bases of RNA).

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The Genetic Code

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  1. The Genetic Code • Gene-a section of DNA that codes for an amino acid sequence (on RNA), which is a building block for proteins. • There are 20 different amino acids made up of three letter words (four letters to choose from-nitrogenous bases of RNA). • These three letter words are called codons • Example: Codon AUG, codes for methionine.

  2. Amino Acids and Codons

  3. Gene ExpressionProtein Synthesis

  4. Simple Summary of Gene Expression/Protein Synthesis • DNA produces an RNA strand in the nucleus • RNA single strand leaves the nucleus through a nuclear pore • RNA enters cytoplasm • RNA attaches to a ribosome • Ribosome and RNA molecule are decoded/”read” and produce a protein

  5. Three Classes of RNA • Messenger RNA (mRNA): Takes a message made from DNA in the nucleus to a ribosome in the cytoplasm

  6. Ribosomal RNA (rRNA): A part of/embedded in the ribosome and the site in which polypeptides are made. (two subunits: small and large ribosome)

  7. Transfer RNA (tRNA): Transfers amino acids to the ribosome (helps translate the message)

  8. From DNA RNA Protein • Step One: Transcription -RNA molecule is made that is complimentary to DNA molecule DNA sequence: AAGCT RNA complimentary sequence: UUCGA -RNA polymerase is the enzyme used to split apart the DNA and join the RNA nucleotides together -messengerR NA (mRNA ) is released into the cytoplasm and reaches a ribosome

  9. transcription

  10. 2. Step Two: Translation: -The information stored on the mRNA is read/translated and codes for a specific amino acid (needed to make the polypeptide protein) • Transfer RNA (tRNA)-bring amino acids to the ribosome (containing rRNA) and is where mRNA gets read/translated

  11. Steps of Translation • Initiation: • A start codon on mRNA, AUG methionine, allows translation to begin • mRNA codon pairs with the complimentary tRNAanticodon • Example codon on mRNA: ACC • Anticodon on tRNA: UGG • The tRNA codes for/attaches to an amino acid • The tRNAsynthetase (enzyme) recognizes which amino acid belongs to which tRNA molecule

  12. Amino Acid tRNAsynthetase helps bind the amino acid to the tRNA molecule tRNA Anticodon mRNA strand codon

  13. II. Elongation-polypeptide gets longer one amino acid at a time III. Termination-synthesis stops due to a stop codon • The three stop codons on the mRNA strand are: ___, ____, ____ • Refer to page 330

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