Lipids

Cholesterol

Cholesterol adds firmness to prevent it from becoming overly fluid, and it also helps maintain its fluidity. All steroid hormones are derived from cholesterol. Cholesterol can be converted into pregnenolone, a 'master hormone', by enzymes. Pregnenolone can then be converted into other numerous vital hormones such as estrogen and testosterone.

Saturated Fat

In a fatty acid chain, there are only single bonds between neighboring carbons in the hydrocarbon chain--this tight packing results in fats that are solid at room temperature. (The thing that fatty acids are saturated with is hydrogen; in a saturated fat, as many hydrogen atoms as possible are attached to the carbon skeleton.)

Unsaturated Fat

There is at least one double bond in the hydrocarbon chain, so there are fewer hydrogens. If there is just one double bond in a fatty acid, it's monounsaturated, while if there are multiple double bonds, it's polyunsaturated. There are two types of unsaturated fat: trans and cis.

Triglycerides

Triglycerides are a type of fat (lipid) found in your blood. If your bloodstream contains more glucose than your body can store as glycogen, your body stores excess glucose as fat cells. Like glycogen, fat is stored for future energy; however, glucose storage as fat can contribute to weight gain and obesity. They are made up of one unit of glycerol and three fatty acids, and can be either saturated or unsaturated.

Phospholipids

are another type of lipid that are major components of the plasma membrane. Like triglycerides, they are typically composed of fatty acid chains attached to a backbone of glycerol. Instead having three fatty acid tails, however, phospholipids generally have just two, and the third carbon of the glycerol backbone is occupied by a modified phosphate group. Fatty acid chains are hydrophobic, whereas the phosphate-containing group is hydrophilic (because of its charge) and interacts readily with water.

Steroids

are the third type of lipids. They are lipids because they are hydrophobic and insoluble in water, but they do not resemble other lipids since they have a structure composed of four fused carbon rings. Steroids include cholesterol, sex hormones (progesterone, estrogen, and testosterone).

Trans Fats

are very rare, with the majority of trans fats being artificially created. They are unsaturated fats with at least one double bond, but unlike "normal" unsaturated fats, trans fats still have a nice, linear structure which makes them a solid. They are artificially created as a by-product of partial hydrogenation.

Hydrogenation

can be either partial or full. Unsaturated fats are hydrogenated to increase their stability so they have a longer shelf-life. Essentially, hydrogenation adds hydrogens to a fatty acid to turn them into a solid. In fully hydrogenated fats, the chains have enough hydrogen added to them to become saturated fats—therefore fully hydrogenated fats cannot be trans fats (which are unsaturated). In partial hydrogenation, however, there are still some double bonds present. Some of these double bonds are of "cis" configuration (normal configuration characteristic for unsaturated fatty acids) and some have been damaged in the process forming a "trans" configuration, where one of the hydrogens at the carbon double bond has been removed and another placed on the opposite side of the chain.

Cis fats

two hydrogens associated with the double bond are on the same side, which generates a kink or bend in the fatty acid that cannot pack together well. So, fats with unsaturated tails tend to be liquid at room temperature (oil).