Genetic code

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Genetic code

  1. 1. Nucleic Acids <ul><li>RNA and Transcription </li></ul><ul><li>The Genetic Code </li></ul><ul><li>Protein Synthesis </li></ul><ul><li>Mutations </li></ul>
  2. 2. Types of RNA <ul><li>Messenger RNA (mRNA) </li></ul><ul><li>Carries genetic information for protein synthesis from DNA in nucleus to the ribosomes </li></ul><ul><li>Transfer RNA (tRNA) </li></ul><ul><li>Small molecules of 20 types that recognize and transfer amino acids for protein synthesis </li></ul><ul><li>Ribosomal RNA (rRNA) </li></ul><ul><li>Makes up 2/3 of ribosomes (1/3 protein) where protein synthesis takes place </li></ul>
  3. 3. Transcription <ul><li>Genetic information contained </li></ul><ul><li>in nucleus </li></ul><ul><li>One strand of DNA is copied </li></ul><ul><li>Complementary bases build mRNA </li></ul><ul><li>DNA(1 strand) mRNA </li></ul><ul><li>In mRNA uracil (U) complements A (DNA) </li></ul><ul><li>New mRNA moves out of nucleus to ribosomes in cytoplasm </li></ul>
  4. 4. Genetic Code <ul><li>Needed to build a particular protein </li></ul><ul><li>The sequence of amino acids is coded by the mRNA </li></ul><ul><li>Each triplet of bases along mRNA codes for an amino acid </li></ul><ul><li>The triplet are called codons </li></ul><ul><li>Codons are known for all 20 amino acids </li></ul><ul><li>Some codons signal the “start” and “end” of a polypeptide chain </li></ul>
  5. 5. Codons and Amino Acids <ul><li>Suppose that a section of a mRNA has the following series of bases. </li></ul><ul><li>CCU –AGC –GGA –CUU </li></ul><ul><li>Use a codon reference to determine the order of amino acids </li></ul><ul><li>CCU = Proline AGC = Serine </li></ul><ul><li>GGA = Glycine CUU = Leucine </li></ul><ul><li>The mRNA codes for the peptide chain of </li></ul><ul><li> Pro –Ser –Gly –Leu </li></ul>
  6. 6. Learning Check G1 <ul><li>What is the order of amino acids coded for by a section of RNA with the base sequence GCC –GUA –GAC ? </li></ul><ul><li>GGC = Glycine GAC = Aspartic acid </li></ul><ul><li>CUC = Leucine GUA =Valine </li></ul><ul><li>GCC = Alanine CGC = Arginine </li></ul>
  7. 7. Solution G1 <ul><li>GGC = Glycine GAC = Aspartic acid </li></ul><ul><li>CUC = Leucine GUA =Valine </li></ul><ul><li>GCC = Alanine CGC = Arginine </li></ul><ul><li> GCC –GUA –GAC </li></ul><ul><li> Ala – Val – Asp </li></ul>
  8. 8. Activation of tRNA <ul><li>Each tRNA binds to its specific amino acid </li></ul>GGG Pro GGG Pro
  9. 9. Anticodons on tRNA <ul><li>A three-base sequence on each tRNA </li></ul><ul><li>Complements a triplet on mRNA </li></ul><ul><li>anticodon </li></ul><ul><li> </li></ul><ul><li>codon on mRNA </li></ul>GGG CCC Pro
  10. 10. Initiation and Elongation <ul><li>mRNA attaches to a ribosome </li></ul><ul><li>tRNA with anticodon UAC binds to first codon (AUG) to initiate synthesis </li></ul><ul><li>The second codon picks up a tRNA with the proper anticodon. </li></ul><ul><li>A peptide bond forms between the amino acids at the first and second codons. </li></ul><ul><li>The first tRNA detaches and the ribosome shifts to the next codon on the mRNA </li></ul>
  11. 11. Peptide Formation <ul><li> Peptide starts to form </li></ul><ul><li>UAC AGA AGA GAG </li></ul><ul><li>• • • • • • • • • • • • </li></ul><ul><li>AUG UCU CUC UCU CUC UUU </li></ul>Met Ser Met Ser Leu
  12. 12. Termination <ul><li>Protein grows as tRNAs bring amino acids to the codons on the mRNA </li></ul><ul><li>When all amino acids for a protein are linked the next codon is “stop” </li></ul><ul><li>There is no tRNA for the “stop” codon </li></ul><ul><li>Protein synthesis ends </li></ul><ul><li>Protein released from ribosome </li></ul>
  13. 13. Learning Check G2 <ul><li>Match the following processes in protein synthesis with the statements: </li></ul><ul><li>(1) Activation (2) Initiation </li></ul><ul><li>(3) Elongation (4) Termination </li></ul><ul><li>A. Ribosome moves along mRNA to add new amino acids to a growing peptide chain </li></ul><ul><li>B. Completed peptide chain released </li></ul><ul><li>C. A tRNA attaches to its specific amino acid </li></ul><ul><li>D. tRNA binds to the AUG codon of the mRNA on the ribosome </li></ul>
  14. 14. Solution G2 <ul><li>Match the following processes in protein synthesis with the statements: </li></ul><ul><li>(1) Activation (2) Initiation </li></ul><ul><li>(3) Elongation (4) Termination </li></ul><ul><li>A. (3) Ribosome moves along mRNA to add new amino acids to a growing peptide chain </li></ul><ul><li>B. (4) Completed peptide chain released </li></ul><ul><li>C. (1) A tRNA attaches to its specific amino acid </li></ul><ul><li>D. (2) tRNA binds to the AUG codon of the mRNA on the ribosome </li></ul>
  15. 15. Learning Check G3 <ul><li>The following section of DNA is used to build a mRNA for a protein. </li></ul><ul><li>GAA-CCC-TTT </li></ul><ul><li>A. What is the corresponding base sequence </li></ul><ul><li>on mRNA? </li></ul><ul><li>B. What are the anticodons for the tRNAs? </li></ul><ul><li>C. What is the amino acid order in the </li></ul><ul><li>peptide? </li></ul>
  16. 16. Solution G3 <ul><li>GAA-CCC-TTT </li></ul><ul><li>A. What is the corresponding base sequence </li></ul><ul><li>on mRNA? </li></ul><ul><li> CUU-GGG-AAA </li></ul><ul><li>B. What are the anticodons for the tRNAs? </li></ul><ul><li>GAA CCC UUU </li></ul><ul><li>C. What is the amino acid order in the </li></ul><ul><li>peptide? </li></ul><ul><li>Leu-Gly-Lys </li></ul>
  17. 17. Mutations <ul><li>Caused by mutagens such as radiation and chemicals </li></ul><ul><li>Alter the nucleotide sequence of DNA </li></ul><ul><li>Produce an incorrect series of codons in the mRNA from the altered DNA </li></ul><ul><li>A different codon binds with a different tRNA </li></ul><ul><li>The protein has one or more wrong amino acids in the peptide sequence </li></ul><ul><li>Can result in a defective protein or enzyme </li></ul>
  18. 18. Examples of Genetic Diseases <ul><li>Galactosemia </li></ul><ul><li>Cystic fibrosis </li></ul><ul><li>Downs syndrome </li></ul><ul><li>Muscular dystrophy </li></ul><ul><li>Huntington’s disease </li></ul><ul><li>Sickle-cell anemia </li></ul><ul><li>Hemophilia </li></ul><ul><li>Tay-Sachs disease </li></ul>

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