Question

Q1) Based on your understanding of amino acid and protein topic answer the following questions. [20 points A) For the following tripeptide: Ala-Gly-Phe O Od -CH -OH CH CH Ala Gly Phe pKI 234 2.34 1.83 pK2 9.67 9.60 9.13 1. Draw separate structures for the three amino acids in this tripeptide at pH=7. 9 points) 2. Calculate the pl for this tripeptide (show your work and your answer should has two decimal points) (6 points) 3. What is the overall charge of this tripeptide at the following pH values: (5 points) PH 1.5 5.0 7.0 9.5 12 Overall charge

Answer 1

Answer 1: The separate structures of Ala, Gly, and Phe at pH 7.0.

COO HUN-C-H CH COO- COO- HIN-C-H СН3 HN-C-H H Alanine Glycine Phenylalanine

Answer 2:

pI = ½ (pK₁+pK₂)

pI of Ala = ½ (2.34+9.67) = 6.00

pI of Gly = ½ (2.34+9.60) = 5.97

pI of Phe = ½ (1.83+9.13) = 5.48

The average of pI for the tripeptide= 1/3 (6.00+5.97+5.48) = 5.81

Answer 3: The pI of the tripeptide is 5.81. If the pH goes below than it pI then peptide will be positively charges and if the pH goes above than pI then it will be negatively charged.

pH	1.5	5	7	9.5	12
Overall charges	Positive	Positive	Positive	Negative	Negative