Ch17-18 trans-bac4-10-06

Ch17-18 trans-bac4-10-06 - What we will cover: 1. How...

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What we will cover: 1. How eukaryotic genes are modified 1. Overview of translation 1. Structure of tRNA 1. Structure of ribosomes
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1. How eukaryotic genes are modified
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Eukaryotic RNA is modified -initial RNA has sequences cut out and ends are modified How are ends modified? -RNA is not stable in cell- enzymes degrade transcript -5’ end has a modified guanine (G) nucleotide -required for export from nucleus and prevents degradation
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-3’ end is cut and 50 to 250 adenine nucleotides added -non-template derived addition- poly-A tail -additions provide: 1. protection from degradation 2. enable export from nucleus to cytoplasm 3. help ribosomes attach to transcript for translation -regions in anterior and posterior are referred to as untranslated regions (UTR)
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RNAs are spliced -eukaryotic RNAs have large portions that are cut out -remaining sequence is put back together- RNA splicing -transcripts average 8000 nucleotides but only 1200 nucleotides to code for average protein -long regions of non-coding are interspersed between coding regions -DNA coding region is not continuous
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-sequences removed are introns -sequences spliced back together are exons -RNA polymerase II transcribes entire region- introns and exons -introns removed and exons spliced together before RNA exits the nucleus
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How is splicing done? -introns contain short sequences recognized by complex of protein and RNA- spliceosome - spliceosome comprised of small nuclear ribonucleoproteins (snRNPs) - RNA and proteins -RNAs recognize the intron sequence for splicing -RNAs also function in catalysis and snRNP assembly
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Ribozymes -some introns are spliced using only RNA -no proteins involved -secondary structure of intron RNA enables catalytic function -intron is able to splice itself out of transcript -proteins are not only catalyst
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What are introns used for? -introns contain control regions- determine when gene is expressed -transcript can code for more than one protein -exons contain domains of proteins -addition or deletions of domains creates related protein with similar but different function - alternative RNA splicing - inclusion or deletion of specific exons
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-alternative splicing enables organism to use less genes -create multiple related proteins from same gene -while proteins are related- may have opposite effects -can produce wide range of proteins from single gene
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2. Overview of translation
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Translation of RNA into peptide -mRNA is read into a polypeptide - transfer RNA (tRNA) reads the codons- use anticodon -individual tRNA for each amino acid- specific amino acid attached to tRNA - ribosome facilitates entry of tRNAs and catalysis of polypeptide elongation
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3. Structure of tRNA
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Transfer RNA structure -transcribed from DNA template -transcribed in nucleus and transported to cytoplasm -in cytoplasm not translated into protein- functional unit is RNA -folding and hydrogen binding creates specific shape to tRNA
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-three dimensional structure is L-shaped -loop at one end is anticodon -other end of L is the amino acid attachment site - 3’ end of molecule
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Ch17-18 trans-bac4-10-06 - What we will cover: 1. How...

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