Final answer:
Globular proteins are soluble due to their structured nature, characterized by hydrophobic amino acids within the core and hydrophilic ones on the surface. In contrast, intrinsically disordered proteins lack a fixed structure and have an amino acid composition that prevents stable folding. Membrane proteins have hydrophobic regions interacting with lipid bilayers.
Step-by-step explanation:
Globular proteins are typically soluble in water due to the amino acid content that dictates their tertiary and quaternary structures. On the other hand, soluble intrinsically disordered proteins lack a fixed or ordered three-dimensional structure due to the absence of certain hydrophobic amino acids that typically stabilize structured proteins.
Globular proteins, such as enzymes, hemoglobin, and serum albumin, have unique amino acid sequences that form specific secondary structures like α-helices and β-pleated sheets. These secondary structures contribute to the overall three-dimensional, folded conformation of the protein, with hydrophobic amino acids usually positioned on the interior and hydrophilic amino acids exposed on the surface, enhancing solubility. In contrast, proteins that are intrinsically disordered contain higher proportions of polar and charged amino acids, lacking significant hydrophobic cores, which contribute to the dynamic, unstructured nature.
Proteins embedded in a lipid bilayer, such as those in plasma membranes, differ by having regions with hydrophobic amino acids interfacing with the lipids, while regions that contact the intra- or extracellular environment generally are richer in hydrophilic amino acids.