i) Discuss the importin-alpha nuclear import cycle, mechanistically accounting for the key steps of nuclear transport. (Essay...

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Biology

i) Discuss the importin-alpha nuclear import cycle,mechanistically accounting for the key steps of nuclear transport.(Essay style include appropriate diagrams)
ii) Quantitative reasoning, 10 marks: During DNA replication,the genome is duplicated as chromatin. How fast does nucleartransport of histones have to take place in terms ofmolecules/pore/second in order to support S-phase in human cells?Assume the genome is 6 x 109 bp, a nucleosome spans 200 bp and that75% of the genome is replicated in the first 3 hr of S-phase.Nuclei contain 2000 nuclear pore complexes. (showwork)

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Importin are composed of a flexible Nterminalimportinbinding IBB domain and a highly structured domaincomprised of ten tandem armadillo ARM repeats The helical ARMrepeats assemble into a twisted sluglike structure whose bellyserves as the cNLSbinding groove The exportin CAS binds to thetenth ARM repeat The flexible IBB domain interacts either intrans with importin or in cis with the cNLSbindinggroove Through these interactions the IBB domain acts as acompetitive inhibitor to regulate binding of cNLS cargo to thebinding groove and when displaced it enables the binding of thecNLS to the nascent targeting See Answer

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