Eukaryotic Test 3 Lecture 8

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Marcusje3
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49651
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Eukaryotic Test 3 Lecture 8
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2010-11-15 01:10:03
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Eukaryotic Test
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Powerpoint 30 (11.10.10)
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  1. RNAs
    Messenger RNAs (mRNAs): RNAs that include mucleotic code info for polypeptide synthesis

    Ribosomal RNAs (rRNA): RNA components of ribosomes

    Transfer RNAs (tRNAS): RNAs that translate the info in the mRNA nucleotide code into AA order of a polypeptide

    Other RNAs: snRNA, snoRNA, siRNA, miRNA
  2. Transcription
    DNA-dependent RNA polymerase (RNA polymerases): Enzymes responsible for transcription in both pro- & eukaryotic

    Template: DNA strand whose sequence is complementary to RNA molecule synthesized from it

    Promoter: the site on DNA to which an RNA polymerase molecule binds prior to initiating transcription

    Transcription factors: Proteins that are required to help RNA polymerases to recognize promoters
  3. Transcription in Prokaryotes
    A single type of RNA polymerase composed of 5 subunits that are tightly associated to form a core enzyme

    Core enzyme can attach to random sites in the DNA to synthesize RNA

    Sigma factor: Accessory polypeptide that increases core enzyme's affinity for promoter sites and decreases its affinity for DNA

    Complete Enzyme (holoenzyme): Associates w/DNA at proper sites and initiates RNA synthesis

    Once 10-12 nt are incorporated into a growing transcript, enzyme will be transformed into a transcriptional elongation complex, followed by release of sigma factor
  4. Transcription and RNA processing in eukaryotic cells
    RNA Polymerase I: Synthesizes larger ribosomal RNAs

    RNA Polymerase II: Synthesizes mRNA and most small nuclear RNAs

    RNA Pol. III: synthesizes various low-molecular-weight RNAs including TRANSFER RNAS
  5. Ribosomal makeup
    More than 80% of RNA in most cells consists of rRNA

    rRNAs and dozens of ribosomal proteins form ribosomes.
  6. Nucleoli (15)
    Nucleoli Function in producing ribosomes

    Bulk of nucleolus is composed of ribosomal subunits that give nucleolus a granular appearance

    • Fc: Contains rDNA
    • dFC: Contains nascent pre-RNA transcripts and associated proteins
    • GC: Contains ribosomal subunits in various stages of assembly
  7. Modifications of pre-RNAs (19)
    100's of methyl gropus are addeds to ribose groups and 95+ Uridine residues are chemically convereted to pseudouridine by the time pre-RNA is 1st cleaved.

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