Question

What are lipoproteins?

Answer 1

A lipoprotein is a biochemical assembly whose purpose is to transport hydrophobic lipid (a.k.a. fat) molecules in water, as in blood or extracellular fluid. They have a single-layer phospholipid and cholesterol outer shell, with the hydrophilic portions oriented outward toward the surrounding water and lipophilic portions of each molecule oriented inwards toward the lipids molecules within the particles. Apolipoproteins are embedded in the membrane, both stabilising the complex and giving it functional identity determining its fate. Thus the complex serves to emulsify the fats. Many enzymes, transporters, structural proteins, antigens, adhesions, and toxins are lipoproteins. Examples include the plasma lipoprotein particles classified as HDL, LDL, IDL, VLDL and ULDL (a.k.a. chylomicrons) lipoproteins, according to density / size (an inverse relationship), compared with the surrounding plasma water. These complex protein capsules enable fats to be carried in all extracellular water, including the blood stream (an example of emulsification), subgroups of which are primary drivers / modulators of atherosclerosis,[1] the transmembrane proteins of mitochondrion, chloroplast, and bacterial lipoproteins.