UMass Amherst BIOLOGY 285 - Bio 285 SI Before Quiz 6 (2 pages)

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Bio 285 SI Before Quiz 6



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Bio 285 SI Before Quiz 6

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2
School:
University of Massachusetts Amherst
Course:
Biology 285 - Cellular & Molecular Biology

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Bio 285 SI Before Quiz 6 The End Replication Problem Basically when newly replicated DNA strand becomes shorter and shorter Happens because the primer is removed so cannot replicate the end of DNA o From lagging strand Primers from lagging strand get taken off except for very last one o Doesn t have anything to be attached to o This creates a gap at 5 end of newly replicated strand That s how cells die and we age Cancer cells don t have this problem why they don t die and they re cancerous At the end of each strand there s a region of DNA called telomere Telomere Coiled at end of DNA being replicated Still part of DNA If telomere didn t exist would think of end of DNA as breakage so would get fixed even though it doesn t need it Consists of repeated DNA sequence In order to prevent telomere from getting shorter cells express telomerase Telomere is part of DNA at the end and telomerase is protein that prevents telomeres from getting shorter How cells solve the end replication problem Telomerase Telomerase is a protein that has an RNA template Job is to extend the parent strand using an RNA template Attaches to the parent strand right before the gap and uses RNA as a template Basically takes that strand and extends it Why want to extend parent strand To attach a primer Need a primer to use as a base to be able to build DNA Gap no primer to replicate to fill gap So need a primer to fill gap need to extend parent strand to get a primer so need telomerase Reverse transcriptase what this process is called use RNA template to make DNA Once you get parent strand get primase to add a primer and then get whole machinery to attach then fill gap and end of replication problem RNA sequence already part of telomerase itself Adding new nucleotides to 3 end of parent strand Using RNA Pro vs Eu how to tell parents from daughters In E coli old strand is methylated how to tell for prokaryotes o Labeling parent strand In eukaryotes don t know how the cell tells o Cell creates a nick in the backbone of the DNA of the newly synthesized strand while replicating o Labeling new strand o Nick becomes fixed after replication over Nick in the DNA Found a mismatch o Parent strand at bottom nick at top because nick on top o Bunch of proteins come in and cleave off mismatch part of newly synthesized strand to cleave off mismatch section and replace it o Need a DNA polymerase need a helicase need a ligase need an endonuclease need an exonuclease need a clamp clamp loader need an ssDNA single stranded DNA binding protein don t need a primase have a 3 end so don t need a primase to build off of already have a base You get a mismatch and recognize



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