Each type of macromolecule has a different function. In looking at the different macromolecules, some generalizations can be made. These are the main characteristics of macromolecules in nature: •
Nucleic acid—this molecule makes genetic information or participates in its transfer to make proteins.
•
Carbohydrate—these will be energy sources but will also form receptors, cell walls, and exoskeletons, and are involved as a food source.
•
Peptides or proteins—these can make enzymes and will be involved in cell structures, receptors, and in nutrient transport.
•
Lipids—these will store energy and make up membrane structures, pigments, and insulation in the organism.
LIPIDS The two main atoms in lipids are carbon and hydrogen but lipids can also have nitrogen, oxygen, phosphorus, and sulfur in them. They provide an energy source for cells, help to store carbon atoms, and are the main structural component of the cell membrane. There are different types of lipid molecules you might encounter in your study of microbiology. Fatty acids are common lipids. They contain long hydrocarbon chains that are hydrophobic because they do not like water and are not soluble in water. Fatty acids that do not have any double bonds but are considered saturated with hydrogen atoms are saturated fatty acids. Fatty acids with one or more double bonds are called unsaturated. There are monounsaturated fatty acids with one double bond and polyunsaturated fatty acids with more than one double bond. Cis-fatty acids are shaped differently than trans fatty acids. Figure 30 shows the different fatty acids:
94
