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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2:05 minutes

Problem 7

Textbook Question

Classify each of the amino acids in problem 16.5 as polar or nonpolar. If polar, indicate if the R group is neutral, acidic, or basic. Indicate if each is hydrophobic or hydrophilic.

Verified step by step guidance

Step 1: Recall the structure of amino acids. Each amino acid has a central carbon atom (α-carbon) bonded to an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a unique R group (side chain). The properties of the R group determine whether the amino acid is polar or nonpolar, and if polar, whether it is neutral, acidic, or basic.

Step 2: Classify the amino acid as polar or nonpolar based on the nature of its R group. Nonpolar amino acids have R groups that are primarily hydrocarbons (e.g., alkyl or aromatic groups), while polar amino acids have R groups containing electronegative atoms like oxygen, nitrogen, or sulfur.

Step 3: For polar amino acids, determine if the R group is neutral, acidic, or basic. Neutral polar amino acids have R groups with polar functional groups (e.g., hydroxyl, amide) but no charge at physiological pH. Acidic amino acids have R groups with carboxylic acid groups that can donate protons, while basic amino acids have R groups with amine groups that can accept protons.

Step 4: Assess whether the amino acid is hydrophobic or hydrophilic. Nonpolar amino acids are generally hydrophobic because their R groups do not interact well with water. Polar amino acids are hydrophilic because their R groups can form hydrogen bonds or ionic interactions with water.

Step 5: Apply these classifications to each amino acid in problem 16.5. For each amino acid, identify the R group, classify it as polar or nonpolar, determine if it is neutral, acidic, or basic (if polar), and indicate whether it is hydrophobic or hydrophilic.

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Key Concepts

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

Amino Acid Classification

Amino acids can be classified based on the properties of their side chains (R groups). They are categorized as polar or nonpolar, which affects their interactions with water. Polar amino acids tend to be hydrophilic, while nonpolar amino acids are generally hydrophobic. Understanding this classification is essential for predicting the behavior of proteins in different environments.

Polar vs. Nonpolar

Polar amino acids have side chains that can form hydrogen bonds with water, making them soluble in aqueous environments. Nonpolar amino acids, on the other hand, have hydrophobic side chains that do not interact favorably with water. This distinction is crucial for understanding protein folding and function, as the distribution of polar and nonpolar residues influences the overall structure of proteins.

Acidic, Basic, and Neutral R Groups

The R groups of polar amino acids can be further classified as acidic, basic, or neutral. Acidic amino acids have side chains that can donate protons (H+), while basic amino acids can accept protons. Neutral amino acids do not have a charge at physiological pH. This classification impacts the amino acids' roles in enzyme activity, protein stability, and interactions with other biomolecules.

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Textbook Question

List the amino acids with side chains that are capable of hydrogen bonding. Draw an example of two of these amino acids hydrogen bonding to one another. For each one, draw a hydrogen bond to water in a separate sketch. Refer to Section 8.2 for help with drawing hydrogen bonds.

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