The type of receptor site it has, determines what type of hormone or neurotransmitter can affect it. If insulin is secreted by an endocrine cell (the beta cell of the pancreatic islets), this hormone will go out of the blood stream and if a cell doesn’t have any insulin receptor sites, the insulin will have not affect it. Membranes are composed of lipids and proteins. The lipids form a bilayer, with the hydrophilic portion of the lipids facing the aqueous environment, and the hydrophobic portions clustering together inside the membrane. The majority of membrane proteins are involved in moving small molecules across the membrane or in energy generation. Lipids: Fatty acids and their derivatives are very important for two reasons, firstly lipids like lecithin, phosphotidyl ethanolamine, sphingolipids, glycolipids, steroids and others are part of the cellular membranes; thus they contribute to the structure of the membranes. Secondly lipids also act as food reserve and provide energy by oxidation. Sep 30, 2017 · Lipids are organic compounds (chemicals built of the element carbon). In addition to carbon atoms, they consist mostly hydrogen, with a relatively low content of oxygen, nitrogen and other elements, as compared to other compounds found in biology. They are hydrophobic, meaning insoluble in water.