Which part of a membrane protein is typically found in contact with the interior of the lipid bilayer?

• A. Phosphate groups
• B. Carbohydrate side chains
• C. Hydrophobic regions
• D. Hydrophilic regions

Answer: (C)

Verified step by step guidance

1. Understand the structure of the lipid bilayer: The lipid bilayer is composed of amphipathic molecules, meaning they have both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions. The interior of the bilayer is hydrophobic, formed by the fatty acid tails of phospholipids.
2. Recognize the nature of membrane proteins: Membrane proteins are also amphipathic. They have hydrophilic regions that interact with the aqueous environment and hydrophobic regions that interact with the lipid bilayer's interior.
3. Identify the regions of the membrane protein: The hydrophobic regions of the protein are typically composed of nonpolar amino acids. These regions are embedded within the hydrophobic core of the lipid bilayer to maintain stability and proper orientation.
4. Eliminate incorrect options: Phosphate groups and carbohydrate side chains are hydrophilic and are found on the exterior of the bilayer, interacting with the aqueous environment. Hydrophilic regions of the protein are also exposed to the aqueous environment, not the bilayer's interior.
5. Conclude the correct answer: The hydrophobic regions of a membrane protein are in contact with the hydrophobic interior of the lipid bilayer, ensuring proper integration and function of the protein within the membrane.