Summary 5.3

Lipids play an important role in our bodies. In more detail, lipids are also compounds that avoid water. The term used for water-avoiding molecules is hydrophobic (water-fearing). Lipids surround and contain the watery contents of our cells, circulate in our bodies and send chemical signals to cells, and store energy in our bodies.

A fat is made up of a three-carbon backbone, glycerol, which is attached to three fatty acids (long hydrocarbon chains). A saturated fat is a fat in which all its three fatty acid chains have the maximum number of hydrogen atoms. In contrast, an unsaturated fat has one or more fatty acid chains with molecules that don't bond with the maximum possible number of hydrogen atoms.

• diets high in saturated fat could be unhealthy
• lipid containing deposits may form (plaques), attaching to blood vessels walls, which may reduce the blood flow and cause heart disease

Steroids are another type of lipid. Steroid molecules are formed from carbon skeletons which make four fused rings. Although steroids are classified as lipids (since they are hydrophobic), they are very different in structure and function from fats. Certain steroids circulate around the body as chemical signs. A commonly known steroid is cholesterol. This steroid is an essential molecule as it is part of the membranes that surround your cells. Cholesterol often has a bad image, since high levels of specific cholesterol-containing substances are linked to cardiovascular disease.

Concept Check

1.What property do lipids share? The property that lipids share is that they are hydrophobic.

2.What are the parts of a fat molecule? The parts of a fat molecule are the glycerol (three-carbon backbone), and the three fatty acids attached to it.

3.Describe two ways that steroids differ from fat.
a)steroids differ from fats in the way they are structured in a four fused ring, while fats are structured with a three-carbon backbone, with three fatty acids attached to it.
b)steroids differ from fats in that steroids circulate in our bodies as chemical signals.

4.What does the term unsaturated fat on a food label mean? The term unsaturated fat on a food label means that the fat within the food have less than the maximum possible number of hydrogen atoms. Unsaturated fat foods are probably more healthy than saturated fat foods.