Lipids

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Overview:

Lipids is a brief unit addressing classification and characteristics of the major groups: fatty acids, glycerides, non-glyderide lipids, and complex lipids. Steroid structure is included.

The ways in which lipids function in the body introduces the unit. From there, the classifications of lipids into four groups is introduced: fatty acids, glycerides, non-glyceride lipids, and complex lipids. Each of these areas is broken down, defined, described, and discussed.

The saturated and unsaturated forms of fatty acids are described and the impact of degree of unsaturation on melting points discussed. Students are encouraged to consider the geometry about the cis structure and the impact of this structure on the close packing of molecules. The student is further encouraged to discover the impact of trans orientation on close packing and to determine what the results in physical properties would be. The way in which trans fatty acids are produced through commercial hydrogenation or “hardening” is discussed.

The section on glycerides introduces glycerides as lipids containing a glycerol structure. The students are then introduced to the glyceride as nothing more than the product of esterification, a process with which they are familiar. Esters of phosphoric acid with glycerol are reviewed as well as esters of carboxylic acids with glycerol. The term “triglyceride” is introduced. The importance of the fat within the triglyceride is discussed in ways other than the concerns about saturated vs. unsaturated fats: taste and texture. The structure and function of an artificial fat that has come to the market is introduced and the way in which this fat works discussed.

Non-glyceride lipids contain sphingolipids, steroids, and waxes, each of which is addressed separately. The sphingolipids are mentioned briefly as phospholipids and the parts discussed. The structure of steroids is discussed and the numbered steroid structure given. Students are given an easy method of learning structures of important steroids such as cholesterol.

Waxes are introduced as esters of a fatty acid and a very long chain alcohol, usually having twenty-four to thirty six carbons. The structure is noted, as is the insolubility in water.
The section on complex lipids stresses the lack of solubility of lipids in polar solvents, such as water. From this, the importance of the plasma lipoprotein as a structure capable of carrying lipids from one part of the body to another is developed.

The unit concludes with a brief look at three of the important plasma lipoproteins: very low density lipoproteins, low density lipoproteins, and high density lipoproteins.