“central dogma of molecular biologyâ€‌ central dogma - central dogma -rna chapter 7...

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  • central dogma -RNA

    chapter 7

    central dogma • “central dogma of molecular biology”

    • originally coined by Francis Crick • not actually dogma • describes how DNA replicates and codes for proteins

    • protein coding • DNA unwinds

    • strands separate • transcription • translation

    amplification • transcription

    • many RNA copies can be made • translation

    • many polypeptide copies can be made from each mRNA

    transcription • initiation

    • strands separate • promoter region

    • elongation • RNA polymerase

    • termination

  • transcription • initiation

    • strands separate • promoter region

    • elongation • RNA polymerase

    • termination

    incoming nucleoside triphosphates

    pre-mRNA transcript

    RNA POLYMERASE

    5’ 5’

    3’

    5’ 3’

    eukaryotic transcription • more complex than prokaryotes

    • 3 different polymerases • require general transcription factors • genes spread out along DNA

    • large variety of regulatory sequences

    • more compact chromatin

    eukaryotic transcription • initiation (PIC complex)

    • general transcription factors 1. TFIID

    • binds to TATA box (~25bp from start) or Inr

    2. TFIIB 3. TFIIF / RNA polymerase II 4. TFIIE - TFIIH

    eukaryotic genomes • processing of mRNAs

    • prokaryotes • mRNA immediately attaches

    to ribosome • eukaryotes

    • capping • splicing • polyadenylation

  • pre-mRNA splicing • splicing pre-mRNAs

    • introns - intervening sequences • exons - expressed sequences • RNA splicing

    • introns must be removed • introns contain splicing signals • carried out by spliceosome

    • snRNPs (small nuclear ribonucleoproteins)

    • splicing can affect protein produced

    • same gene may produce different proteins

    exporting mRNA • mRNA export

    • poly-A-binding proteins • cap-binding complex • exon junction complex

    • proteins bound to sites of connected exons • nuclear pore complex

    • properly tagged mRNA is exported

    • messenger RNA - • carries message

    about polypeptide • contains a sequence

    of codons • three base

    sequence • codes for an

    amino acid

    RNA RNA • transfer RNA

    • present in the cytoplasm • carry the 20 amino acids • charged by aminoacyl-tRNA synthetases • anticodon

  • • ribosomes • large subunit

    • 3 tRNA binding sites • 2x as big (mass)

    • small subunit • mRNA binding site

    E P A

    assembly

    G G G U U U U GC UG C

    translation • three phases

    • initiation • elongation

    • codon recognition • peptide bond formation • translocation

    • termination

    • three phases • initiation • elongation

    • codon recognition • peptide bond formation • translocation

    • termination

    translation ribosomes • polyribosomes

    • often multiple ribosomes act on mRNA • multiple copies at once

    • bound ribosomes • polypeptide signals binding