Which of the following groups of amino acid residues would likely be found in the portion that crosses the lipid bilayer?
a. Acidic
b. Basic
c. Polar uncharged
d. Nonpolar

Verified step by step guidance

1. Understand that the lipid bilayer is a hydrophobic environment, meaning it repels water and is composed mainly of nonpolar molecules.
2. Recognize that amino acids with nonpolar side chains are more likely to be found in the hydrophobic core of the lipid bilayer because they do not interact with water.
3. Identify the nonpolar amino acids from the image: Glycine (Gly), Alanine (Ala), Valine (Val), Leucine (Leu), Isoleucine (Ile), Methionine (Met), Cysteine (Cys), Phenylalanine (Phe), Tryptophan (Trp), and Proline (Pro).
4. Consider that polar, acidic, and basic amino acids are more likely to be found on the exterior of the protein or in aqueous environments because they can form hydrogen bonds or ionic interactions with water.
5. Conclude that the group of amino acid residues most likely to be found in the portion that crosses the lipid bilayer is the nonpolar group.

Key Concepts

Lipid Bilayer Structure

The lipid bilayer is a fundamental component of cell membranes, composed of two layers of phospholipids. The hydrophobic (water-repelling) tails face inward, while the hydrophilic (water-attracting) heads face outward. This arrangement creates a barrier that separates the interior of the cell from the external environment, influencing which molecules can pass through.

Amino Acid Properties

Amino acids can be classified based on their side chains (R groups) into categories such as polar, nonpolar, acidic, and basic. Nonpolar amino acids have hydrophobic side chains that do not interact favorably with water, making them more likely to be found in the lipid bilayer, while polar and charged amino acids tend to be hydrophilic and interact with the aqueous environment.

Transmembrane Proteins

Transmembrane proteins span the lipid bilayer and often contain regions that interact with both the hydrophobic core of the membrane and the aqueous environments on either side. The portions of these proteins that cross the bilayer typically consist of nonpolar amino acids, allowing them to stabilize within the hydrophobic environment of the membrane.