Textbook Question
For each of the following proteins, note whether the main secondary structure feature is α helix, β-pleated sheet, or both.
a. collagen
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18. Amino Acids and Proteins
Secondary Protein Structure
Problem 102a
Textbook Question
Globular proteins are water-soluble, whereas fibrous proteins are insoluble in water. Indicate whether you expect the following amino acids to be on the surface of a globular protein or on the surface of a fibrous protein.
a. Ala
Verified step by step guidance1
Understand the difference between globular and fibrous proteins: Globular proteins are water-soluble and typically have hydrophilic (water-attracting) amino acids on their surface, while fibrous proteins are water-insoluble and often have hydrophobic (water-repelling) amino acids on their surface.
Analyze the properties of alanine (Ala): Alanine is a nonpolar amino acid with a methyl group (-CH₃) as its side chain. Nonpolar side chains are hydrophobic, meaning they do not interact well with water.
Determine the likely location of alanine in a globular protein: Since alanine is hydrophobic, it is more likely to be found in the interior of a globular protein, away from the aqueous environment, rather than on the surface.
Determine the likely location of alanine in a fibrous protein: In fibrous proteins, which are typically insoluble in water, hydrophobic amino acids like alanine are often found on the surface, as these proteins are not exposed to a water-soluble environment.
Conclude the placement: Alanine is expected to be on the surface of a fibrous protein due to its hydrophobic nature, but it would likely be buried in the interior of a globular protein to avoid interaction with water.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Globular Proteins
Globular proteins are spherical in shape and are typically water-soluble due to their hydrophilic (water-attracting) side chains. This solubility allows them to function effectively in various biological processes, such as enzyme activity and transport. Their structure is stabilized by various interactions, including hydrogen bonds and hydrophobic interactions, which influence the positioning of amino acids within the protein.
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Fibrous Proteins
Fibrous proteins are elongated and insoluble in water, primarily serving structural roles in organisms. They are composed of long chains of amino acids that form strong, stable structures, such as collagen in connective tissues and keratin in hair and nails. The insolubility of fibrous proteins is due to their hydrophobic (water-repelling) side chains, which aggregate to form fibers that provide strength and support.
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Amino Acid Properties
Amino acids possess distinct properties based on their side chains (R groups), which can be classified as hydrophobic, hydrophilic, acidic, or basic. These properties determine the location of amino acids within proteins; hydrophobic amino acids tend to be buried in the interior of globular proteins, while hydrophilic amino acids are often found on the surface. Understanding these properties is crucial for predicting the behavior of specific amino acids, such as alanine (Ala), in different protein environments.
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