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Chapter 15.

2005-2006. Code is redundantseveral codons for each amino acid

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Chapter 15.

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    1. 2005-2006 Chapter 15.

    2. 2005-2006 Code is redundant several codons for each amino acid “wobble” in the tRNA “wobble” in the aminoacyl-tRNA synthetase enzyme that loads the tRNA Universal code Strong evidence for a single origin in evolutionary theory.Strong evidence for a single origin in evolutionary theory.

    3. 2005-2006 Mutations Point mutations single base change base-pair substitution silent mutation no amino acid change redundancy in code missense change amino acid nonsense change to stop codon

    4. 2005-2006 Point mutation leads to Sickle cell anemia What kind of mutation?

    5. 2005-2006 Sickle cell anemia

    6. 2005-2006 Mutations Frameshift shift in the reading frame changes everything “downstream” insertions adding base(s) deletions losing base(s)

    7. 2005-2006

    8. 2005-2006 Chapter 17.

    9. 2005-2006 Transcription -- another look The process of transcription includes many points of control when to start reading DNA where to start reading DNA where to stop reading DNA editing the mRNA protecting mRNA as it travels through cell

    10. 2005-2006 Primary transcript Processing mRNA protecting RNA from RNase in cytoplasm add 5’ cap add polyA tail remove introns

    11. 2005-2006 Protecting RNA 5’ cap added G trinucleoside (G-P-P-P) protects mRNA from RNase (hydrolytic enzymes) 3’ poly-A tail added 50-250 A’s protects mRNA from RNase (hydrolytic enzymes) helps export of RNA from nucleus

    12. 2005-2006 Dicing & splicing mRNA Pre-mRNA ? mRNA edit out introns intervening sequences splice together exons expressed sequences In higher eukaryotes 90% or more of gene can be intron no one knows why…yet there’s a Nobel prize waiting… average size gene (transcription unit) = 8000 bases average size primary transcript = 8000 bases average size mature RNA = 1200 bases average size protein = 400 amino acids lots of “junk DNA”average size gene (transcription unit) = 8000 bases average size primary transcript = 8000 bases average size mature RNA = 1200 bases average size protein = 400 amino acids lots of “junk DNA”

    13. 2005-2006 Discovery of Split genes

    14. 2005-2006 snRNPs small nuclear RNA RNA + proteins Spliceosome several snRNPs recognize splice site sequence cut & paste RNA as ribozyme some mRNA can splice itself RNA as enzyme Splicing enzymes

    15. 2005-2006 Ribozyme RNA as enzyme

    16. 2005-2006 Splicing details No room for mistakes! editing & splicing must be exactly accurate a single base added or lost throws off the reading frame

    17. 2005-2006 Alternative splicing Alternative mRNAs produced from same gene when is an intron not an intron… different segments treated as exons

    18. 2005-2006 Domains Modular architecture of many proteins separate functional & structural regions coded by different exons in same “gene”

    19. 2005-2006 The Transcriptional unit (gene?)

    20. 2005-2006 Any Questions??

    21. 2005-2006 The Transcriptional unit

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