Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

18. Amino Acids and Proteins

Amino Acid Classifications

GOB Chemistry

18. Amino Acids and Proteins

Amino Acid Classifications

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2:26 minutes

Problem 12b

Textbook Question

Glycine has the zwitterion structure shown. Draw the structure and give the net charge of glycine that will predominate at the indicated pH values (pI = 6.0).
b. pH 12.0

Verified step by step guidance

Understand the concept of a zwitterion: A zwitterion is a molecule that has both positive and negative charges but is overall electrically neutral. Glycine, an amino acid, exists as a zwitterion at its isoelectric point (pI), which is pH 6.0 in this case.

At pH values above the pI (e.g., pH 12.0), the environment is basic, meaning there is a low concentration of H⁺ ions. This will affect the protonation state of glycine's functional groups.

Identify the functional groups in glycine: Glycine has an amino group (-NH₃⁺ in its protonated form) and a carboxylic acid group (-COO⁻ in its deprotonated form). At pH 12.0, the amino group will lose a proton, becoming -NH₂, while the carboxylic acid group remains deprotonated as -COO⁻.

Determine the net charge: At pH 12.0, the amino group (-NH₂) is neutral, and the carboxylate group (-COO⁻) carries a negative charge. Therefore, the net charge of glycine at pH 12.0 is -1.

Draw the structure: The structure of glycine at pH 12.0 will have the central carbon atom bonded to a hydrogen atom, a -CH₂ group, a neutral -NH₂ group, and a negatively charged -COO⁻ group. This reflects the deprotonated state of glycine in a basic environment.

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Key Concepts

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

Zwitterion Structure

A zwitterion is a molecule that has both positive and negative charges but is overall neutral. In the case of amino acids like glycine, the amino group (-NH3+) carries a positive charge, while the carboxyl group (-COO-) carries a negative charge. This dual charge allows zwitterions to exist in a stable form in solution, particularly at physiological pH levels.

Isoelectric Point (pI)

The isoelectric point (pI) is the pH at which a molecule, such as an amino acid, carries no net electrical charge. For glycine, the pI is 6.0, meaning that at this pH, the positive and negative charges balance out. Understanding the pI is crucial for predicting the charge of glycine at different pH levels, which influences its solubility and interactions in biological systems.

pH and Charge Relationship

The pH of a solution affects the ionization state of amino acids. At pH values below the pI, glycine will predominantly exist in its positively charged form, while at pH values above the pI, it will exist in its negatively charged form. At pH 12.0, which is significantly above the pI, glycine will predominantly be negatively charged due to the deprotonation of the amino group.

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Textbook Question

Give the three-letter and one-letter abbreviations and identify the functional group in the side chain for each amino acid in Problem 10.1.

a. alanine

b. lysine

c. tryptophan

d. aspartate

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Textbook Question

Draw the structure for each of the following amino acids and put an asterisk (*) next to any chiral carbon centers in your structure:

c. methionine

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Textbook Question

Classify each amino acid in Problem 10.4 as polar (neutral, acidic, or basic) or nonpolar and as hydrophobic or hydrophilic.

a. leucine

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c. methionine

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Textbook Question

Isoleucine has the zwitterion structure shown. Draw the structure and give the net charge of isoleucine that will predominate at the indicated pH values (pI = 6.0).

b. pH 6.0

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Textbook Question

Consult Table 18.3 and draw alanine. Label the functional groups and give the three-letter abbreviation and the one-letter abbreviation. What group does the side chain fall into?

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Draw the structure of glutamic acid at low pH, at high pH, and at the two forms that exist between low pH and high pH. Which of these structures represents the zwitterion?

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Name and draw the structures of the amino acids that fit the following descriptions:

a. Contains an isopropyl group

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Name and draw the structures of the amino acids that fit the following descriptions:

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Glycine has the zwitterion structure shown. Draw the structure and give the net charge of glycine that will predominate at the indicated pH values (pI = 6.0).b. pH 12.0

Key Concepts

Zwitterion Structure

Isoelectric Point (pI)

pH and Charge Relationship

Watch next

Glycine has the zwitterion structure shown. Draw the structure and give the net charge of glycine that will predominate at the indicated pH values (pI = 6.0).
b. pH 12.0