Biological Systems MCAT Practice Exam 2025 – The Comprehensive All-in-One Guide for Exam Success!

Insulin is classified as a peptide hormone because it is composed of chains of amino acids. Peptide hormones are typically synthesized as larger precursor proteins and then cleaved to form the active hormone. In the case of insulin, it is produced in the pancreas from a larger protein called proinsulin, which is then converted into the active form through enzymatic cleavage.

Peptide hormones are generally water-soluble, which allows them to travel freely in the bloodstream and bind to specific receptors on the surface of target cells, initiating various cellular responses. Insulin, in particular, plays a crucial role in glucose metabolism by facilitating the uptake of glucose into cells, especially muscle and fat cells, thereby lowering blood sugar levels.

In contrast, steroid hormones are derived from cholesterol and can easily pass through cell membranes, binding to intracellular receptors. Amino acid derivatives are modified forms of single amino acids and typically function in various signaling pathways, while fatty acid hormones are derived from fatty acids and usually play roles in longer-term signaling related to metabolism and inflammation. Each hormone class has unique structural characteristics and physiological roles, which help in understanding their functions in the body.