5. refer to model 2 for the information relevant to this question. a sample of t

Question

5. refer to model 2 for the information relevant to this question. a sample of the peptide Lys-Glu-Ser has a net charge of zero between what two pH values? what is the pI of Lys-Glu-Ser?

Model 2 pKa 8.5 pKa 3.5 CH2 CH2 CH2 CH2 CH2 CH CH pka- 10.0 O" NH3 COOH H3N COOHHaN COOH COOH/ NH3 NH3 NH3 COO- At pH 3.5 the C terminal is half proton-At pH-4.2 the R group carboxyl is half ated and half deprotonated. At pH-1 all groups are protonated. protonated, half deprotonated. NET charge +2 NET charge = +1.5 NET charge 0.5 coo-H2N Coo H2N coo H3N H2N OH coo- coo coo NH2 NH3 /NH2 At pH#8.5 the N terminal is half protonated and half deprotonated At pH-10.0 the R group amino of lysineAt pH-12 all groups are deprotonated. is half protonated, half deprotonated. NET charge-2.0 NET charge1.5 NET charge--0.5

Explanation / Answer

pl is pH at which net charge is zero .

As given in model the between pH 4.2and 8.5 net charge is +0.5 and -0.5 respectively so between these two pH the net charge will be zero.

So pl =1/2(4.2+8.5) =1/2 ×12.7 = 6.4

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