Difference Between Cholesterol And Fat
Cholesterol, a waxy substance synthesized by all vertebrates, is the best-known member of the sterols, a biologically important group of lipid alcohols. Cholesterol is the major sterol of vertebrate tissues and is also important in many invertebrates. Because of its role in heart disease in humans, cholesterol has been the focus of much debate over what constitutes healthy or unhealthy levels of cholesterol in the blood and how to reduce cholesterol in the diet.
Cholesterol’s major functions in higher animals are as a component of various cell membranes and as a precursor of other important sterols. The cholesterol content of a membrane varies with the tissue and with specific membrane function. For example, the lipids of human myelin membrane, a sheathlike structure that wraps, insulates, and protects nerve axons, contain 25–30% cholesterol. Outer cell (plasma) membranes are multifunctional, serving to both contain and protect the contents of a cell while also mediating critical receptor, transport, and metabolic functions. In humans, plasma membrane lipids contain about 10% cholesterol. The mitochondrion and endoplasmic reticulum, internal cellular organelles that have almost exclusively metabolic functions, contain less than 5% cholesterol in their membrane lipids.
In addition to its structural role in biomembranes, cholesterol is the precursor to four groups of steroids important in humans and most other mammals. These include sex hormones (androgens and estrogens), adrenal corticosteroids (for example, corticosterone and aldosterone), D vitamins, and the bile acids. Bile acids are predominantly found conjugated to the amino acids glycine and taurine to form bile salts. These are stored in the gallbladder and secreted into the intestine during food intake, where they aid in the digestion and absorption of dietary lipids. Although most of the secreted bile salts are reabsorbed for further use, 5–10% per day are normally lost by excretion in feces. This loss represents the only significant pathway for the removal of cholesterol from the body and is critically important for cholesterol homeostasis.
Fats are a class of energy-rich organic compounds of plant or animal origin, which are basic components of animal diets. Fats differ from oils in that they are solid or semisolid at room temperature, while oils are liquid. Fats and oils are primarily compounds of long-chain fatty acids and glycerol, which is a trihydroxy alcohol. Natural waxes, such as beeswax, which are closely related to fats and oils, also contain fatty acids; however, in wax these acids are combined with monohydroxy alcohols (although a few exceptions involve dihydroxy alcohols).
In animal metabolism fats and oils give far more energy per unit weight than either proteins or carbohydrates; they supply about 9 kilocalories per gram (kcal/gram) compared to 4 kcal/gram for proteins and sucrose. Fats and oils are also used as raw materials for the preparation of paints, soaps, detergents, cosmetics, greases, candles, and softening agents for rubber and plastics.