Optometry Admission Test (OAT) Practice

What role do peptides play in the endocrine system?

1. They are responsible for hormone synthesis

2. They act as secondary messengers

3. They bind to DNA

4. They stimulate muscle contraction

The correct answer is: They act as secondary messengers

Peptides have a significant role in the endocrine system primarily as signaling molecules, particularly as hormones that can act through secondary messenger pathways. Certain peptides, known as peptide hormones, are released by endocrine glands and bind to specific receptors on target cells. Unlike steroid hormones that can pass through the cell membrane and directly alter gene expression, peptide hormones typically interact with receptors that are linked to secondary messenger systems. When a peptide hormone binds to its receptor on the cell surface, it activates a cascade of intracellular processes through secondary messengers, such as cyclic AMP (cAMP) or inositol triphosphate (IP3). These secondary messengers amplify the signal and initiate various cellular responses, including metabolic changes, gene expression, or the secretion of other hormones. In contrast, the other options refer to different processes or elements that do not accurately describe the function of peptides in the context of the endocrine system. Hormone synthesis is primarily the role of endocrine glands, while binding to DNA is characteristic of steroid hormones. The stimulation of muscle contraction is associated more with other types of signaling molecules such as neurotransmitters and not specifically with peptide hormones in general. Thus, understanding the role of peptides as signaling substances that utilize secondary messenger systems is essential in grasping their function