Final answer:
Integral membrane proteins can be incorporated into the phospholipid bilayer via alpha-helices, beta-sheets, single-pass transmembrane segments, or multiple hydrophobic regions. These proteins have secondary structures that interact with the hydrophobic core of the lipid bilayer and hydrophilic regions that interface with the cell's internal and external environments.
Step-by-step explanation:
Integral membrane proteins can be incorporated into the phospholipid bilayer using various methods, and different secondary structures are associated with them. One way is through alpha-helices that span the membrane. For example, a protein may have one or more alpha-helices consisting of hydrophobic amino acids that interact with the hydrophobic core of the phospholipid bilayer. Another way is the incorporation of beta-sheets that fold back and forth across the membrane, forming a beta-barrel structure. Such proteins might form channels or pores through the membrane.
Proteins may also associate with the membrane by having a single-pass transmembrane segment composed of 20-25 hydrophobic amino acids. Moreover, some more complex proteins embed within the membrane through multiple hydrophobic regions, potentially comprising up to 12 segments that are extensively folded and anchored in the bilayer, with hydrophilic regions remaining exposed to the cytosol or extracellular fluid.
Finally, integral membrane proteins that do not span the entire membrane may still be anchored through a hydrophobic helix, with functionality provided by their hydrophilic domains interacting with surrounding molecules, contributing to cell structure and function.