Advanced Placement (AP) Biology Practice Exam

Which type of isomer has distinct biological functions due to structural differences?

1. Structural isomers

2. Geometric isomers

3. Enantiomers

4. All listed types of isomers

The correct answer is: All listed types of isomers

Distinct biological functions arising from structural differences are a hallmark of various types of isomers. Structural isomers have the same molecular formula but differ in the connectivity of their atoms, leading to unique properties and functions in biological systems. For example, glucose and fructose are structural isomers that participate in different metabolic pathways despite having the same formula (C6H12O6). Geometric isomers, also known as cis-trans isomers, arise due to the arrangement of groups around a double bond. This spatial configuration can significantly influence the biological activity of molecules. For instance, the difference in configuration can affect the way a molecule interacts with enzymes or receptors, leading to varying physiological responses. Enantiomers, a specific type of stereoisomer, are non-superimposable mirror images of each other. This structural distinction can lead to drastically different biological effects. A classic case is the enantiomers of the drug thalidomide; one form was effective as a sedative, while the other caused severe birth defects. Each type of isomer—structural, geometric, and enantiomers—demonstrates how slight variations in structure can yield significant differences in biological function. This highlights the importance of molecular structure in biochemistry and pharmacology. Thus