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Proteins, Proteins, Proteins!

What is the connection between genes (DNA) & phenotype? IOW, how, exactly, do genes determine who we are?. Proteins, Proteins, Proteins! Many are structural in nature, but most traits are determined by enzymes (or lack thereof!) Transcription & translation link genes to proteins

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Proteins, Proteins, Proteins!

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  1. What is the connection between genes (DNA) & phenotype?IOW, how, exactly, do genes determine who we are? Proteins, Proteins, Proteins! • Many are structural in nature, but most traits are determined by enzymes (or lack thereof!) • Transcription & translation link genes to proteins DNA  RNA  protein transcription translation

  2. One gene, one-enzyme hypothesis • Proposed by Garod, 1909 • Confirmed by Beadle & Tatum, 1930 • Worked w/ neurospora (bread mold) mutants • Modified to one gene, one polypeptide

  3. Overview

  4. The Triplet Code • 3 bases on DNA specify a particular amino acid • A gene contains enough triplet codes to specify a particular polypeptide chain,along with regulatory DNA

  5. The genetic code • Refers specifically to mRNA codons • Complementary to DNA triplets • Universal • Degenerate • Wobble DNA- CCA/GGT/TTT/CGA RNA- GGU/CCA/AAA/GCU Aminos - gly/pro/lys/ala

  6. DNA- CCA/GGT/TTT/CGA m RNA- GGU/CCA/AAA/GCU tRNA- CCA/GGU/UUU/CGA Aminos - gly/ pro/ lys/ ala Aminos - gly/pro/lys/ala

  7. Transcription-mRNA synthesis • 3 stages-initiation, elongation, termination • Catalyzed by RNA polymerase(synthesizes 5’  3’) • DNA is organized into Transcription units (genes) • Initiation sequence, triplet codes for polypeptide, termination • Per gene, only one strand of DNA is transcribed(template, anti-sense) • Which strand may vary from gene to gene

  8. initiation • RNA pol binds to promoter • Promoter includes binding site & • initiation site • RNA pol unzips DNA & begins • Putting Complementary bases in place

  9. elongation New strand is built in 3’ to 5’ direction Uracil instead of thymine Uses nucleoside triphosphates

  10. termination • Terminator sequence (DNA) • Signals end of polypeptide • RNA pol dissociates, DNA • zips up, mRNA released

  11. In nucleus Promoter includes the TATA box (for transcription factors) Transcription units only contain info for1 polypeptide chain mRNA must be processed before translation In cytoplasm No TATA box or transcription factors Transcription units may contain info for several different polypeptide chains, but have 1 set of regulators No mRNA processing Translation can take place simultaneously w/ transcription Eukaryotes vs prokaryotes

  12. RNA processing • Methylguanosine “cap” added to 5’end • Protection,Ribosomal attachment • Poly-A tail added to 3’ end • Protection,Transport to cytoplasm • INTRONS (intervening sequences) cut out • EXONS left & spliced together • Spliceosomes-proteins (enzymes) & RNA • Alternative RNA processing

  13. RNAi (interference) • Post-transcriptional gene silencing • Short Double-stranded RNA (siRNA) triggers degradation of homologous mRNA • May be protective (proofreading) • research

  14. The Anti-Codon • Complementary to codons • Found on tRNA • “cloverleaf” shape • Attachment site for amino acid • Anti codon at opposite end • 1 tRNA per amino acid • Aminoacyl tRNA synthetase • Inosine (U,C, or A)

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