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Biology MCQs




Question;1) Find kcat for a reaction in which Vmax is 8 x 10-3 mol/min and the reaction mixture contains two microgram of enzyme (the molecular weight of the enzyme is 100,000 D).2) An enzyme is considered to have evolved to its most efficient form ifA) kcat is a large numberB) kcat/KM is near the diffusion-controlled limitC) KM is a large numberD) kcat/KM is a very small numberE) KM is a small number3) Determine the subunit composition of this protein from the following information:Molecular mass of the native protein by gel filtration is 400 kDMolecular mass by SDS-PAGE is 200 kDMolecular mass by SDS-PAGE with 2-mercaptoethanol is 100 kD, 60 kD, and 40 kD4) Treatment of a short peptide with trypsin gives four fragments with sequences:Leu-ArgTyr-Thr-Ser-Val-Trp-Trp-Gly-LysGln-Leu-Phe-Phe-Thr-Leu-ArgAla-Asp-Glu-Asn-LysCleavage of the same peptide with chymotrypsin gives six fragments with the sequences:Thr-Leu-Arg-Leu-Arg-Ala-Asp-Glu-Asn-Lys-TyrThr-Ser-Val-TrpGln-Leu-PheGly-LysPheTrpWhat is the sequence of the intact peptide?5) Treatment of a polypeptide with 2-mercaptoethanol yields two polypeptides:(A) Val-Met-Cys-Arg-Gly-Gly-Phe-Arg-Cys-Leu-Ser(B) Gly-Gln-Asp-Cys-Tyr-Val-Ile-Lys-Glu-Cys-ThrTreatment with trypsin yields fragments with the following amino acid compositions:Cys2, Glu, Leu, Ser, ThrArg, Gly2, PheArg, Asp, Cys2, Gln, Gly, Ile, Lys, Met, Tyr, Val2Using the two polypeptides above (A and B), indicate the positions of the disulfide bonds in the intact polypeptide.Analysis of a peptide indicates that there is NO free animo terminal group. Digestion with trypsin yields three peptides with the sequences Ile-Cys-Met-Lys, Asp-Gln-Trp-Asp-Thr-Phe-Lys, and Ser-Gly-Tyr-Arg. Digestion with chymotrypsin yields three peptides with the sequences Arg-Asp-Gln-Trp, Asp-Thr-Phe, Lys-Ile-Cys-Met-Lys-Ser-Gly-Tyr. Draw a diagram of the original peptide.


Paper#63168 | Written in 18-Jul-2015

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