Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

29. Amino Acids

Acid-Base Properties of Amino Acids

Organic Chemistry

29. Amino Acids

Acid-Base Properties of Amino Acids

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5:57 minutes

Problem 8b

Textbook Question

Draw the predominant form for glutamate in a solution with the following
pH: b. 3

Verified step by step guidance

Determine the pKa values of the functional groups in glutamate. Glutamate has three ionizable groups: the α-carboxyl group (pKa ≈ 2.1), the α-amino group (pKa ≈ 9.5), and the side-chain carboxyl group (pKa ≈ 4.1).

Compare the pH of the solution (pH = 3) to the pKa of each functional group to determine their protonation states. If pH < pKa, the group will be protonated; if pH > pKa, the group will be deprotonated.

Analyze the α-carboxyl group (pKa ≈ 2.1): Since pH (3) > pKa (2.1), the α-carboxyl group will be deprotonated, forming a carboxylate ion (\( \text{COO}^- \)).

Analyze the side-chain carboxyl group (pKa ≈ 4.1): Since pH (3) < pKa (4.1), the side-chain carboxyl group will remain protonated as \( \text{COOH} \).

Analyze the α-amino group (pKa ≈ 9.5): Since pH (3) < pKa (9.5), the α-amino group will remain protonated as \( \text{NH}_3^+ \). Combine these observations to draw the predominant form of glutamate at pH 3.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Amino Acid Structure

Amino acids, the building blocks of proteins, consist of a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable R group. Glutamate, specifically, has a side chain that contains a carboxyl group, making it an acidic amino acid. Understanding the structure of glutamate is essential for predicting its behavior in different pH environments.

pH and Protonation States

pH is a measure of the acidity or basicity of a solution, influencing the protonation state of molecules. At low pH (like 3), amino acids can exist in their protonated forms, where the carboxyl group is likely to be protonated (–COOH) and the amino group remains protonated (–NH3+). This affects the overall charge and predominant form of glutamate in solution.

Zwitterions

Zwitterions are molecules that have both positive and negative charges but are overall neutral. In the context of amino acids, at physiological pH, they often exist as zwitterions. However, at a low pH like 3, glutamate will predominantly exist in a protonated form, which is crucial for understanding its behavior in biochemical processes and interactions.

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d. pH=12

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Draw the form of aspartate that predominates at the following pH values:

d. pH=11.0

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Draw the form of aspartate that predominates at the following pH values: c. pH=6.0

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Draw the predominant form for glutamate in a solution with the following pH:

a. 0

Textbook Question

c. Which amino acid has the greatest amount of negative charge at pH = 6.20?

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Draw the pH–activity profile for an enzyme that has one catalytic group at the active site:

a. the catalytic group is a general-acid catalyst with a pK_a = 5.6.

Textbook Question

Draw the pH–activity profile for an enzyme that has one catalytic group at the active site:

b. the catalytic group is a general-base catalyst with a pKa = 7.2.

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Draw the predominant form for glutamate in a solution with the following pH: b. 3

Key Concepts

Amino Acid Structure

pH and Protonation States

Zwitterions

Watch next

Draw the predominant form for glutamate in a solution with the following
pH: b. 3