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  • 1. Protein Synthesis Section 3.5Thank you Mr. Taylor for the use of several slides
  • 2. Gene Expression RNA (ribonucleic acid)
  • 3. Gene Expression Three Classes of RNA – Messenger RNA (mRNA)  Takes a message from DNA to the ribosomes  Codon  Transcription – Ribosomal RNA (rRNA)  Makes up ribosomes (along with proteins) – Transfer RNA (tRNA)  Transfers amino acids to ribosomes  Anticodon  Translation
  • 4. Gene Expression Gene Expression Requires Two Steps: – Transcription – Translation
  • 5. Overview: the roles of transcription and translation in the flow of genetic information (Layer 1)
  • 6. Overview: the roles of transcription and translation in the flow of genetic information (Layer 2)
  • 7. Overview: the roles of transcription and translation in the flow of genetic information (Layer 3)
  • 8. Overview: the roles of transcription and translation in the flow of genetic information (Layer 4)
  • 9. Overview: the roles of transcription and translation in the flow of genetic information (Layer 5)
  • 10. IT’S ANN’Y TIME
  • 11. Transcription
  • 12. Gene Expression Transcription – During transcription, a segment of the DNA serves as a template for the production of an RNA molecule – Formation of Messenger RNA (mRNA)  RNA polymerase binds to a promoter  DNA helix is opened so complementary base pairing can occur – HELICASE!  RNA polymerase joins new RNA nucleotides in a sequence complementary to that on the DNA – Messenger RNA formed - CODON  Strand carries code for protein  Is complementary to the section of DNA
  • 13. Transcription of DNA to form mRNA
  • 14. Translation
  • 15. ANNY TIME
  • 16. Gene Expression Transfer RNA - ANTICODON – tRNA transports amino acids to the ribosomes – Single stranded nucleic acid that correlates a specific nucleotide sequence with a specific amino acid – Amino acid binds to one end, the opposite end has an anticodon – the order of mRNA codons determines the order in which tRNA brings in amino acids
  • 17. Transfer RNA: Amino Acid Carrier
  • 18. Gene Expression Translation (overview) – In cytoplasm/ribosome – mRNA - Triplet codon: AUG initiates translation – tRNA – attached to certain amino acids – corresponds to anticodon --- complementary to codon – mRNA bonds to tRNA – H bonds – 20 different enzymes for each amino acid – Needs ATP – 2 amino acids make peptide bond – continues – Stop codon: UAA, UAG, UGA – nonsense codon – mRNA fragment – returns to nucleus
  • 19. Translation
  • 20. Translation
  • 21. Translation
  • 22. The Genetic Code
  • 23. Overview of Gene Expression
  • 24. Genetic Code- The Genetic Code  Triplet code- each 3-nucleotide unit of a mRNA molecule is called a CODON  There are 64 different mRNA codons – 61 code for particular amino acids  Redundant code-some amino acids have numerous code words  Provides some protection against mutations – 1 start codon – AUG – also codes for a.a. - MET – 3 are stop codons signal polypeptide termination
  • 25. Messenger RNA Codons
  • 26. Gene ExpressionDegenerate – two or more codons code for the same amino acidUniversal – all living organisms use the same code (including viruses)(Transcribe and Translate a Gene)
  • 27. One Gene, One Polypeptide 1940’s (Beadle and Tatum) – one gene will always make one enzyme. Became – One Gene, One Polypeptide Hypothesis Really One Allele, One Protein – Exceptions  Some genes do not produce polypeptides  Some genes code for RNA which does not produce a polypeptide. - (no start codon)
  • 28. Summary of Gene Expression
  • 29. END
  • 30. Gene Expression Ribosome and Ribosomal RNA – Ribosome has a binding site for mRNA and for 2 tRNAs – Facilitate complementary base pairing – Ribosome moves along mRNA and new tRNAs come in and line up in order – This brings amino acids in line in a specific order to form a polypeptide – Several ribosomes may move along the same mRNA  Multiplecopies of a polypeptide may be made  The entire complex is called a polyribosome
  • 31. Polyribosome Structure and Function
  • 32. mRNA Processing