Advanced Placement (AP) Biology Practice Exam

What is the carbon skeleton structure of steroids?

1. Three fused rings

2. Four fused rings

3. A linear chain

4. Two separate chains

The correct answer is: Four fused rings

The carbon skeleton structure of steroids is characterized by four fused rings. This distinctive configuration is essential in defining the structure and function of steroid molecules, which include important biological compounds such as cholesterol, hormones like testosterone and estrogen, and various vitamins. The four-ring structure consists of three cyclohexane rings and one cyclopentane ring, which are fused together in specific orientations. This arrangement allows for a great diversity of chemical modifications that lead to different steroid functions and properties, influencing processes such as metabolism, inflammation, and immune response. Understanding this foundational structure is crucial because it highlights how variations in the functional groups attached to these rings can significantly alter the biological effects of different steroids.