Table of contents

1. Introduction to Biochemistry4h 34m
2. Water3h 23m
3. Amino Acids8h 10m
4. Protein Structure10h 4m
5. Protein Techniques14h 5m
6. Enzymes and Enzyme Kinetics13h 38m
7. Enzyme Inhibition and Regulation 8h 42m
8. Protein Function 9h 41m
9. Carbohydrates7h 49m
10. Lipids5h 49m
11. Biological Membranes and Transport 6h 37m
12. Biosignaling9h 45m
Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m

4. Protein Structure

Isoelectric Point of a Peptide

Biochemistry

4. Protein Structure

Isoelectric Point of a Peptide

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Multiple Choice

Estimate the isoelectric point of the following dipeptide in the figure.

4.75

9.5

10.5

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Verified step by step guidance

Identify the amino acids in the dipeptide. The structure shows a dipeptide composed of cysteine and histidine.

Determine the pKa values for the ionizable groups in the dipeptide. Cysteine has a side chain pKa around 8.3, and histidine has a side chain pKa around 6.0. The amino group has a pKa around 9.0, and the carboxyl group has a pKa around 2.0.

List all the pKa values: pKa1 (carboxyl group) = 2.0, pKa2 (histidine side chain) = 6.0, pKa3 (cysteine side chain) = 8.3, pKa4 (amino group) = 9.0.

To find the isoelectric point (pI), identify the pKa values that correspond to the zwitterionic form of the dipeptide. This is typically between the pKa of the side chain of histidine and the amino group.

Calculate the isoelectric point (pI) by averaging the pKa values that flank the zwitterionic form: pI = (pKa2 + pKa4) / 2.