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

3. Amino Acids

Isoelectric Point of Amino Acids with Ionizable R-Groups

Biochemistry

3. Amino Acids

Isoelectric Point of Amino Acids with Ionizable R-Groups

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Multiple Choice

Calculate the pI of Arg. pK_a1 = 9. pK_a2 = 2.2. pK_R = 12.5.

1.9

10.75

3.6

12.5

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Verified step by step guidance

Identify the ionizable groups in arginine: the carboxyl group (pKa1 = 2.2), the amino group (pKa2 = 9.0), and the side chain guanidinium group (pKR = 12.5).

Determine the charge of arginine at different pH levels. At low pH, all groups are protonated, and as the pH increases, they lose protons in the order of their pKa values.

To find the isoelectric point (pI), identify the pH at which the molecule has a net charge of zero. For arginine, this occurs between the pKa values of the groups that lose protons to achieve a neutral charge.

Since arginine has a positively charged side chain, the pI is calculated using the average of the pKa values of the amino group and the side chain guanidinium group, which are the two groups that will be neutral at the pI.

Calculate the pI using the formula: pI = (pKa2 + pKR) / 2. Substitute the given values: pI = (9.0 + 12.5) / 2.