Final answer:
Hydrophobic membrane-spanning regions of integral membrane proteins are mainly exposed to the hydrophobic core of the lipid bilayer. These regions consist of 20-25 amino acids and enable the protein to integrate into the membrane, with hydrophilic parts protruding for interaction with aqueous environments.
Step-by-step explanation:
The portion of a membrane protein that is exposed to the hydrophobic core of the lipid bilayer is primarily constituted by hydrophobic membrane-spanning regions. Integral membrane proteins, also known as integrins, contain these regions that integrate seamlessly within the membrane, allowing them to interact with the hydrophobic interior formed by the fatty acid tails of the phospholipids. These proteins often have single-pass hydrophobic transmembrane segments which can be composed of 20-25 amino acids and span from one side of the membrane to the other. Complex membrane proteins can consist of multiple such segments, making them capable of extensive folding and integration into the membrane.
The arrangement of the protein's regions positions the hydrophobic sections adjacent to the phospholipid tails and the hydrophilic regions protruding from the membrane. This alignment allows the protein to interact with both the cytosol and extracellular fluid with its hydrophilic parts while remaining anchored in the membrane due to its hydrophobic traits.