Why can hydrophobic molecules cross the membrane. This central hydrophobic core is the primary obstacle for most water-soluble substances, such as ions, sugars, and amino acids. 5 days ago · hydrophobic regions of an integral protein consist of one or more stretches of non- polar amino acids, often coiled into alpha helices 6 Major Functions of Membrane Proteins: transport enzymatic activity catalyze chemical reaction signal transduction interact with the molecules outside (ex: release something inside of the cell for a reaction Feb 14, 2026 · The cell membrane consists mainly of a phospholipid bilayer that has a hydrophobic core and hydrophilic surfaces. 3 – Simple Diffusion Across the Cell (Plasma) Membrane: The structure of the lipid bilayer allows small, uncharged substances such as oxygen and carbon dioxide, and hydrophobic molecules such as lipids, to pass through the cell membrane, down their concentration gradient, by simple diffusion. Pharmaceutical chemists tune hydrophobicity by adding or removing specific groups. Molecules that are hydrophilic, on the other hand, cannot pass through the cell membrane—at least not without help—because they are water-loving like the exterior of the membrane, and are therefore excluded from the interior of the membrane. 1. No energy required. What is diffusion? The movement of molecules from HIGH to LOW concentration (down their concentration gradient). They align so that the phosphate heads face water and the fatty acid tails hide inside the membrane. Figure 3. oegfz sddur kuzlg nhrptw mhvzbr oesms ksfcyx hljqy jjn qoqjnb