1a)Determine the net charge of the following tetrapeptide at pH 4 that contains

Question

1a)Determine the net charge of the following tetrapeptide at pH 4 that contains the amino acids represented by the single letters “KILT”, such that K is at the amino-terminal end of the peptide and T is at the carboy-terminal end.

A. +2

B. +1

C. 0

D. -1

E. -2

1b)What is the isoelectric point of the following tetrapetide that contains the amino acids represented by the single letters “TLIK”, such that T is at the amino-terminal end of the peptide and K is at the carboy-terminal end.

A. 9.51

B. 10.00

C. 10.07

D. 9.11

E. 10.61

A. +2

B. +1

C. 0

D. -1

E. -2

1b)What is the isoelectric point of the following tetrapetide that contains the amino acids represented by the single letters “TLIK”, such that T is at the amino-terminal end of the peptide and K is at the carboy-terminal end.

A. 9.51

B. 10.00

C. 10.07

D. 9.11

E. 10.61

Explanation / Answer

Amino acids

1a) The net charge on the tetrapeptide, KILT,

looking at the pKa values for theamino acids forming the peptide we can calculate net charge on peptide

So at pH 4.00, all -NH2 will be in -NH3+ state and -COOH would be in -COO- state

net charge,

B. +1

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1b) Isoelectric point is the point when the net charge on the species is zero.

For the given tetrapeptide TLIK,

the isoelectric point can be calculated by pKa of the side chains and the -NH2 of T, and -COOH of K,

isoelectric point for peptide = 1/2(9.10 + 10.53) = 10.00 (rounded off)

B. 10.00

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