Advanced Placement (AP) Biology Practice Exam

What are isomers?

1. Molecules with different molecular formulas

2. Molecules with the same molecular formula but different structures

3. Molecules that cannot form stable bonds

4. Molecules with the same structure and properties

The correct answer is: Molecules with the same molecular formula but different structures

Isomers are defined as molecules that share the same molecular formula but have different structures or arrangements of their atoms. This difference in structure can lead to variations in their physical and chemical properties, making isomers an important concept in understanding molecular biology and chemistry. There are various types of isomers, specifically structural isomers and stereoisomers, that illustrate how slight changes in connectivity or spatial orientation can create distinct compounds. For instance, structural isomers differ in the connectivity of their atoms, while stereoisomers have the same connectivity but differ in their three-dimensional arrangement. The existence of isomers is fundamental in various biological processes, as the specific structure of a molecule often determines its function and interaction with other biological molecules, such as enzymes and receptors. This concept is crucial in fields like drug design, where the activity of a compound can be heavily influenced by its isomeric form.