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Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
Genetic code
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Genetic code

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  • 1. Nucleic AcidsRNA and Transcription The Genetic Code Protein Synthesis Mutations 1
  • 2. Types of RNA• Messenger RNA (mRNA) Carries genetic information for protein synthesis from DNA in nucleus to the ribosomes• Transfer RNA (tRNA) Small molecules of 20 types that recognize and transfer amino acids for protein synthesis• Ribosomal RNA (rRNA) Makes up 2/3 of ribosomes (1/3 protein) where protein synthesis takes place 2
  • 3. Transcription• Genetic information contained in nucleus• One strand of DNA is copied• Complementary bases build mRNA DNA(1 strand) mRNA• In mRNA uracil (U) complements A (DNA)• New mRNA moves out of nucleus to ribosomes in cytoplasm 3
  • 4. Genetic Code• Needed to build a particular protein• The sequence of amino acids is coded by the mRNA• Each triplet of bases along mRNA codes for an amino acid• The triplet are called codons• Codons are known for all 20 amino acids• Some codons signal the “start” and “end” of a polypeptide chain 4
  • 5. Codons and Amino AcidsSuppose that a section of a mRNA has thefollowing series of bases. CCU–AGC –GGA –CUUUse a codon reference to determine the order ofamino acids CCU = Proline AGC = Serine GGA = Glycine CUU = LeucineThe mRNA codes for the peptide chain of Pro –Ser –Gly –Leu 5
  • 6. Learning Check G1What is the order of amino acids coded for bya section of RNA with the base sequence GCC–GUA –GAC ?GGC = Glycine GAC = Aspartic acidCUC = Leucine GUA =ValineGCC = Alanine CGC = Arginine 6
  • 7. Solution G1GGC = Glycine GAC = Aspartic acidCUC = Leucine GUA =ValineGCC = Alanine CGC = Arginine GCC –GUA –GAC Ala – Val – Asp 7
  • 8. Activation of tRNAEach tRNA binds to its specific amino acid Pro Pro GGG GGG 8
  • 9. Anticodons on tRNA• A three-base sequence on each tRNA• Complements a triplet on mRNA Pro anticodon GGG CCC codon on mRNA 9
  • 10. Initiation and Elongation• mRNA attaches to a ribosome• tRNA with anticodon UAC binds to first codon (AUG) to initiate synthesis• The second codon picks up a tRNA with the proper anticodon.• A peptide bond forms between the amino acids at the first and second codons.• The first tRNA detaches and the ribosome shifts to the next codon on the mRNA 10
  • 11. Peptide Formation Peptide starts to form MetMet Ser Ser LeuUAC AGA AGA GAG• •• • •• • • • •• •AUG UCU CUC UCU CUC UUU 11
  • 12. Termination• Protein grows as tRNAs bring amino acids to the codons on the mRNA• When all amino acids for a protein are linked the next codon is “stop”• There is no tRNA for the “stop” codon• Protein synthesis ends• Protein released from ribosome 12
  • 13. Learning Check G2 Match the following processes in protein synthesis with the statements: (1) Activation (2) Initiation (3) Elongation (4) TerminationA. Ribosome moves along mRNA to add new amino acids to a growing peptide chainB. Completed peptide chain releasedC. A tRNA attaches to its specific amino acidD. tRNA binds to the AUG codon of the mRNA on the ribosome 13
  • 14. Solution G2 Match the following processes in protein synthesis with the statements: (1) Activation (2) Initiation (3) Elongation (4) TerminationA. (3) Ribosome moves along mRNA to add new amino acids to a growing peptide chainB. (4) Completed peptide chain releasedC. (1) A tRNA attaches to its specific amino acidD. (2) tRNA binds to the AUG codon of the mRNA on the ribosome 14
  • 15. Learning Check G3The following section of DNA is used to builda mRNA for a protein. GAA-CCC-TTTA. What is the corresponding base sequence on mRNA?B. What are the anticodons for the tRNAs?C. What is the amino acid order in the peptide? 15
  • 16. Solution G3 GAA-CCC-TTTA. What is the corresponding base sequence on mRNA? CUU-GGG-AAAB. What are the anticodons for the tRNAs? GAA CCC UUUC. What is the amino acid order in the peptide? Leu-Gly-Lys 16
  • 17. Mutations• Caused by mutagens such as radiation and chemicals• Alter the nucleotide sequence of DNA• Produce an incorrect series of codons in the mRNA from the altered DNA• A different codon binds with a different tRNA• The protein has one or more wrong amino acids in the peptide sequence• Can result in a defective protein or enzyme 17
  • 18. Examples of Genetic DiseasesGalactosemiaCystic fibrosisDowns syndromeMuscular dystrophyHuntington’s diseaseSickle-cell anemiaHemophiliaTay-Sachs disease 18

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