3. Given is the primary sequence of the following pentapeptide I R T H D (Ile-Arg-Gly-His-Asp). a) Write out the peptide's structural formula at pH 1. Indicate all asymmetric carbon atoms with asterisks. What is the net charge of the peptide? b) Number protons in the order of their dissociation, and attach pKa values from the provided list on page 1. c) Indicate the charge of each ionizable group at pH 9 and determine the peptide's net charge. ionizable group pKa approx. charge at pH 9
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2. Study the following amino acid sequence and answer the questions {a, b, c, d, e, f and g}. Asp-Gln-Glu-Asn (a) Write out the complete structure (NB: attached and visible handwritten structure is accepted) with the charges that you would expect at pH 0.0. IMPORTANT: YOUR ANSWERS MUST BE IN A TABLE FORMAT FOR QUESTIONS THAT FOLLOW: b) Write out all ionisable groups in an order increasing pKa values. c) Calculate the net charge on the molecule at pH 0.0 d) Calculate the net charge on the molecule at pH 3.0 e) Calculate the net charge on the molecule at pH 7.0 f) Calculate the net charge on the molecule at pH 9.8 g) Calculate the pI of the peptide
Suman K.
What would be the approximate net charge of the peptide shown below at pH = 7.3? To facilitate answering this question, assume that the N-terminal aminium group has a pKa of 8, the C-terminal carboxyl group has a pKa of 3.5, and that the ionizable side chains have pKas as follows: Asp = 4.0, Glu = 4.0, His = 6, Cys = 8.4, Tyr = 10, Lys = 10, and Arg = 12.5. Also, assume that if the pH is at least two units above or below the pKa of a particular group, then that group is completely unprotonated or protonated, as the case may be. Report your answer to the nearest hundredth.
Supreeta N.
Who's charged? Draw the structure of the dipeptide GlyHis. What is the charge on the peptide at pH $5.5 ?$ pH $7.5 ?$
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