Consider the peptide: H2N - Asp – Thr – Phe - Lys – COOH (1) (2) (3) (4) What is

ID: 197071 • Letter: C

Question

Consider the peptide:

H2N - Asp – Thr – Phe - Lys – COOH

(1) (2) (3) (4)

What is the primary sequence of the peptide above.

(1) (2) (3) (4) ---------(This is the residue #)

H2N – D -T – F – K – COOH

The questions did not provide concentration. (This question is about Isoelectric points and interaction of 20 Amino Acids)

Use the one letter amino acid code and identify from N-terminus to C-terminus.

1. Determine the PI (isoelectric point) of the peptide. (Round to 2 decimal points)

The pI (isoelectric point) value is from the textbook, Lehninger's principle of Biochemistry, 5th edition.

Table 3-1 Properties and Conventions Associated with the Common Amino Acids Found Proteins

https://www.dropbox.com/s/g3fjghh71oeac5c/Lehninger 5th Edition.pdf?dl=0

Which type of noncovalent interaction would the indicated residue sidechain make at the given PH?

(H-bond, Hydrophobic or Vander Waals, or Ionic bond or Salt bridge)

2. Residue 1 @ pH 5.0

3. Residue 2 @ pH 6.0

4. Residue 3 @ pH 11.0

5. Residue 4 @ pH 10.0

6. Calculate the fraction of the peptides C-terminus protonated at pH 2.5 (Round to 2 decimal points)

Ans 1) The isolectric point of Asp = (1.88+3.65)/2 = 2.77

The isolectric point of Thr = (2.11+9.62)/2 = 5.89

The isolectric point of Phe = (1.83+9.13) /2 = 5.48

The isolectric point of lys = (8.95+10.53)/2 = 9.74

The isolectric point of the peptide is (9.74+5.48+5.89+2.77)/4 = 5.97

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