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BIOL 2020
K Wheaton

sAll mRNA’s are? Genes in euk are? Spliced , discontinuous RNA pol I transcription results in? single precursor that encodes three RNA components of the ribosome (18S, 28S, 5.8S) What are tRNAs Most processed of all RNA pol III transcripts. Prok-nucleotides from 5’ end (leader) on the precursor cleaved by RNase P, 3’ end removed, CCA nucleotides added by CCA adding enzyme. Euk-heavily modified on base and ribose moieties, pre-tRNAs are splieced by endonuclease and ligase Introns vs. Extrons Intragenic (inside area of DNA that doesn’t code for protein), expressed (code for protein) Describe the mRNA cap and how it contributes 5’ triphosphate end of nascent RNA chain is to stability modified, phphoryl group released (hydrolysis), diphosphate 5’ end attacks phosphorus atom of GTP, forms 5’-5’ triphosphate linkage. CAP. N7 atom of terminal G, methylated by S- adenosylmethionine to form cap0. Adjacent riboses can form cap 1 or 2. Enhance translation Describe the polyA tail DNA does not encode this, primary transcripts contain hundreds of nucleotides beyond 3’ end that are removed before polyA tail is added. The end is generated by endonuclease that recognizes AAUAAA, it is present in the mature mRNA. Adds 250 adenylate residues on teh 3’ end, use ATP as donor, added after cap Describe splicing Introns excised and exons linked Exon-intron boundaries Introns begin with GU and end with AG. Sequence at 5’ splice site AGGUAAGU, 3’ end of intron 10 pyrimidines (U/C) polypyrimidine tract, followed by any base and then C ending with AG, internal site between 20-50 nucleotides (3 splice site) introns length (50- 10000 nucleotides) Mutations in splicing causes? Genetic disorders, hemoglobin (3 exons and 2 introns) cis-acting mutations can occur at 5’ or 3’. Premature termination signal, defective mRNA usually degraded, 15% of all genetic diseases come from splicing Alternate splicing Different combos of exons, selected by trans- acting splicing factors to cis-acting sequences in pre-mRNA, leads to changes in coding sequence, different proteins, expands versatility of genomic sequences Genetic disease caused by splicing defect Breast cancer, hemophilia..... Describe acute intermittent porphyria and Low levels of porphobilinogen deaminase symptoms that occur after a change such as (PGBD)enzyme involved in heme biosynthesis diet symptoms: abdominal pain, urinary sumptoms, peripheral neuropathy, motor weajness, electrolyte abnormalities Molecular biology of acute intermittent Two isoforms (from promoters) transcribed porphyria ---dont have to know specifics (exons 1, 3-15) and (exons 2-15) 149 mutations that result in this disease, deletions, insertions, frame shifts RNA functioning as a catalyst Called ribozymes, came from knowledge of tetrahymena (ciliated protozoan), 414- nucleotide intron is removed. Can function as an enzyle....catalyzes splicing Self splicing Group I intron, requires added guanosine or guanine nucleotide, serves as energy source incorporated into RNA, attacks 5’ splice site
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