One molecule of glycerol joins together with three fatty acid molecules to form a triglyceride molecule, in another condensation polymerisation reaction.
Phospholipids have a similar structure to triglycerides, but with a phosphate group in place of one fatty acid chain. There may also be other groups attached to the phosphate. Phospholipids have a polar hydrophilic head and two non-polar hydrophobic tails.
They may form a double-layered phospholipids bilayer. This traps a compartment of water in the middle separated from the external water by the hydrophobic sphere. This structure is called a liposome, and is similar to a membrane surrounding a cell.
Waxes are formed from fatty acids and long-chain alcohols. They are commonly found wherever waterproofing is needed, such as in leaf cuticles, insect exoskeletons, birds' feathers and mammals' fur.
Steroids are small hydrophobic molecules found mainly in animals. They include: cholesterol, which is found in animals cell membranes to increase stiffness, bile salts, which help to emulsify dietary fats, steroid hormones such as testosterone, oestrogen, progesterone and cortical and vitamin D, which aids Ca2+ uptake by bones.
Unsaturated fats are usually liquid at room temperature. They are found in most vegetable products and oils. An exception is a group of tropical oils like coconut or palm kernel oil which are highly saturated. Using foods containing "polyunsaturated" and "monounsaturated" fats does not increase our risk of heart disease. However, like all fats, unsaturated fats give us 9 calories for every gram. So eating too much of these types of fat may also make us gain weight.
We can reduce the fat and unsaturated fats in our diets by using less fat, oil, and margarine. We can also eat more low-fat foods like vegetables, fruits, breads, rice, pasta and cereals. Read and compare food labels to find foods that have less total fat.
Saturated fats are usually solid or almost solid at room temperature. All animal fats, such as those in meat, poultry, and dairy products are saturated. Processed and fast foods are also saturated. Vegetable oils also can be saturated. Palm, palm kernel and coconut oils are saturated vegetable oils. (Fats containing mostly unsaturated fat can be made more saturated through a process called "hydrogenation." See the definition for hydrogenated/partially hydrogenated.")
Saturated fats are the very unhealthy fats. They make the body produce more cholesterol, which may raise blood cholesterol levels. Excess saturated fat is related to an increased risk of cardiovascular disease. The amount of cholesterol found in foods is not as important as the amount of saturated fat. Of all the fats, saturated fat is the most potent determinant of blood cholesterol levels. Saturated fats stimulate the production of LDL cholesterol (“bad” cholesterol) and therefore increase blood cholesterol levels and the risk of heart disease. Saturated fats raise cholesterol levels and LDL-cholesterol levels more than dietary cholesterol itself.
Triglycerides are insoluble in water. They are used for storage, insulation and protection in fatty tissue (or adipose tissue) found under the skin (sub-coetaneous) or surrounding organs. They yield more energy per unit mass than other compounds so are good for energy storage. Carbohydrates can be mobilised more quickly, and glycogen is stored in muscles and liver for immediate energy requirements.
Triglycerides containing saturated fatty acids have a high melting point and tend to be found in warm-blooded animals. At room temperature they are solids (fats), e.g. butter, lard, and Triglycerides containing unsaturated fatty acids have a low melting point and tend to be found in cold-blooded animals and plants. At room temperature they are liquids (oils), e.g. fish oil, vegetable oils.
Fatty acids are long molecules with a polar, hydrophilic end and a non-polar, hydrophobic tail. The hydrocarbon chain can be from 14 to 22 CH2 units long, but it is always an even number because of the way fatty acids are made.