A fatty acid with one or more double or triple bonds is known as a unsaturated fatty acid. When this occurs, the fatty acid can absorb additional hydrogen atoms. They may also exhibit cis or trans conformations depending on which side of the double bond adjacent hydrogen atoms appear.
Cis conformations have adjacent hydrogen atoms on the same side of the carbon-carbon double bond. Trans conformations have adjacent hydrogen atoms on opposite sides of the double bond. Differences in the conformation of the molecules affect biological structures and processes. Fatty acids may also be categorized as monosaturated or polyunsaturated. Unsaturated fatty acids can undergo addition and substitution reactions.