Several segments of the polypeptide chain of integral membrane proteins usually span the lipid bilayer. These segments frequently (NOT RELATED)
**Core Concept**
The polypeptide chain of integral membrane proteins spans the lipid bilayer through hydrophobic segments, which are rich in nonpolar amino acids. These nonpolar segments interact with the hydrophobic tails of phospholipid molecules, allowing the protein to anchor itself within the lipid bilayer.
**Why the Correct Answer is Right**
The hydrophobic segments of integral membrane proteins, also known as transmembrane domains, are crucial for their integration into the lipid bilayer. These segments are formed by a specific arrangement of nonpolar amino acids, such as alanine, valine, and leucine, which create a hydrophobic environment. This environment enables the transmembrane domains to interact with the hydrophobic tails of phospholipid molecules, thereby stabilizing the protein within the lipid bilayer. The transmembrane domains are typically 20-25 amino acids in length and have a specific secondary structure, such as alpha-helices, which facilitate their integration into the lipid bilayer.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify the hydrophobic nature of the segments that span the lipid bilayer.
**Option B:** This option is incorrect because it does not provide a clear description of the segments that span the lipid bilayer.
**Option C:** This option is incorrect because it is a distractor that does not relate to the correct answer.
**Clinical Pearl / High-Yield Fact**
The arrangement of nonpolar amino acids in transmembrane domains is crucial for their integration into the lipid bilayer. A common mnemonic to remember the nonpolar amino acids that form transmembrane domains is "AVL" (alanine, valine, and leucine).
**Correct Answer:** A. Hydrophobic segments.