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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Problem 8

Textbook Question

Which amino acid is hydrophilic (dissolves in aqueous solutions)? Why?
a. isoleucine
b. phenylalanine
c. aspartic acid

Verified step by step guidance

Identify the chemical properties of each amino acid listed in the options. Amino acids can be classified as hydrophilic (water-loving) or hydrophobic (water-fearing) based on the nature of their side chains (R groups).

Examine isoleucine: Isoleucine has a nonpolar, aliphatic side chain. Nonpolar side chains are hydrophobic because they do not interact well with water molecules.

Examine phenylalanine: Phenylalanine has a nonpolar, aromatic side chain. Aromatic side chains are generally hydrophobic because they lack polar groups that can form hydrogen bonds with water.

Examine aspartic acid: Aspartic acid has a polar, negatively charged side chain due to the presence of a carboxylate group (-COO⁻). Charged and polar side chains are hydrophilic because they can form hydrogen bonds and interact with water molecules.

Conclude that aspartic acid is hydrophilic because its negatively charged side chain allows it to dissolve in aqueous solutions, while isoleucine and phenylalanine are hydrophobic due to their nonpolar side chains.

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Key Concepts

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

Hydrophilicity

Hydrophilicity refers to the property of a molecule that allows it to interact favorably with water. Hydrophilic substances tend to be polar or charged, enabling them to form hydrogen bonds with water molecules, which facilitates their dissolution in aqueous solutions. This property is crucial in biological systems, as it influences the solubility and transport of molecules within cells.

Amino Acid Structure

Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid consists of a central carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group) that determines its properties. The nature of the side chain influences whether the amino acid is hydrophilic or hydrophobic, impacting protein structure and function.

Polar vs. Nonpolar Side Chains

Amino acids can be classified based on the characteristics of their side chains as polar (hydrophilic) or nonpolar (hydrophobic). Polar side chains contain functional groups that can form hydrogen bonds with water, making them soluble in aqueous environments. In contrast, nonpolar side chains are hydrophobic and tend to aggregate away from water, which is essential for the folding and stability of proteins.

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Related Practice

Textbook Question

Which form of aspartic acid in Problem 18.54 is the zwitterion? What is the pI for the zwitterion?

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Open Question

Classify each amino acid as polar, nonpolar, acidic, or basic.

a) Glu

b) Val

c) Pro

d) Lys

e) Gln

f) Arg

828

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Multiple Choice

Provide one letter codes for amino acids with neutral hydrophilic R groups that participate in H bonding.

562

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Textbook Question

Valine is an amino acid with a nonpolar side chain and serine is one with a polar side chain. Draw the two amino acids.

a. Why is the side chain for valine nonpolar, whereas the side chain for serine is polar?

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Textbook Question

Cell membranes are studded with proteins. Some of these proteins, involved in the transport of molecules across the membrane into the cell, span the entire membrane and are called transmembrane proteins. The interior of the cell membrane is hydrophobic and nonpolar, whereas both the extracellular and intracellular fluids are water-based.

a. List three amino acids you would expect to find in the part of a transmembrane protein that lies within the cell membrane.

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Textbook Question

Four of the most abundant amino acids in proteins are leucine, alanine, glycine, and valine. What do these amino acids have in common? Would you expect these amino acids to be found on the interior or on the exterior of the protein?

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Textbook Question

Is phenylalanine hydrophilic or hydrophobic? Explain why.

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Textbook Question

Which of the following amino acids is most likely to be found on the outside of a soluble protein, and which of them is more likely to be found on the inside? Explain each answer. (Hint: Consider the effect of the amino acid side chain in each case and that the protein is folded up into its globular form.)

a. Valine

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