1. a. For the following two peptides, draw the chemical structure of both peptides,indicating where...

Question

1. a. For the following two peptides, draw the chemical structure of both peptides,indicating where the peptide bonds are.
(i) Pro-Lys-Phe-Asp (ii) His-Tyr-Arg-Trp
b. Draw a titration curve for both of these peptides. Be sure to label the axesproperly, indicate the pKa values, the equivalence points and the bufferingregions.
c. What is the pI value of the peptides. Show how you determine your answer.

David · Accepted Answer

PI of the polypeptide can be determined from the Pka of amino and carboxylic groups of the 
amino acids.  
Pka 1 (Pka of carboxylic group of aspartic acid) = 2.09 
Pka2 (Pka of carboxylic group of side chain of aspartic acid) = 3.86 
Pka 3 (Pka of side chain of lysine) = 10.53 
Pka 4 (Pka of amino group of proline) = 10.64 
When pH is below 2, proton of carboxylic group of aspartate will release and charge of amino 
acid would be +1. 
When pH is below 3, proton from the side chain carboxyl group of the aspartate will be 
discharged and the charge of polypeptide would be 0 
When pH is above 11,

1. a. For the following two peptides, draw the chemical structure of both peptides,indicating where the peptide bonds are. (i) Pro-Lys-Phe-Asp (ii) His-Tyr-Arg-Trp b. Draw a titration curve for both...

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