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 110a

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

Verified step by step guidance

Step 1: Understand the context of the problem. Proteins in their globular form fold in such a way that hydrophilic (water-attracting) amino acid side chains are typically found on the outside of the protein, where they can interact with water, while hydrophobic (water-repelling) side chains are usually buried on the inside, away from water.

Step 2: Analyze the amino acid in question, valine. Valine is a nonpolar amino acid with a hydrophobic side chain consisting of a branched alkyl group (isopropyl group). This makes valine less likely to interact with water.

Step 3: Apply the principle of hydrophobicity. Since valine has a hydrophobic side chain, it is more likely to be found on the inside of a soluble protein, where it can avoid contact with the aqueous environment.

Step 4: Consider the overall structure of the protein. The folding of the protein into its globular form is driven by the hydrophobic effect, which minimizes the exposure of hydrophobic residues like valine to water, stabilizing the protein structure.

Step 5: Conclude that valine is more likely to be found on the inside of a soluble protein due to its hydrophobic nature, and explain that hydrophilic amino acids (not valine) would be more likely to be found on the outside, interacting with the aqueous environment.

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Key Concepts

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

Amino Acid Properties

Amino acids have distinct properties based on their side chains (R groups), which can be classified as hydrophobic, hydrophilic, acidic, or basic. Hydrophobic amino acids, like valine, tend to avoid water and are usually found in the interior of proteins, while hydrophilic amino acids are more likely to be on the exterior, interacting with the aqueous environment.

Protein Folding

Proteins fold into specific three-dimensional shapes, a process driven by the interactions between amino acid side chains. This folding results in a globular structure where hydrophobic residues are buried inside to minimize exposure to water, while hydrophilic residues are exposed on the surface, facilitating interactions with the surrounding environment.

Solubility of Proteins

The solubility of a protein in water is influenced by the distribution of hydrophilic and hydrophobic amino acids. Soluble proteins typically have a higher proportion of hydrophilic amino acids on their surface, allowing them to interact favorably with water, while hydrophobic amino acids are sequestered within the protein's core.

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Related Practice

Textbook Question

Which amino acid is hydrophilic (dissolves in aqueous solutions)? Why?

a. isoleucine

b. phenylalanine

c. aspartic acid

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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

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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Textbook Question

What are some differences between each of the following pairs?

c. polar and nonpolar amino acids

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Textbook Question

How does the polarity of the R group in leucine compare to the R group in serine?

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Textbook Question