Chapter 45, Problem 1IQ

Label the parts of the following diagrams, indicating which parts represent a water-soluble hormone and which a lipid-soluble hormone.

Summary Introduction

To label: The parts of the given diagram by indicating the parts that represent a water-soluble hormone and a lipid-soluble hormone.

Introduction: Hormones are small molecules that act as chemical messengers in the body. They regulate the body processes by binding to their specific receptors. For lipid-soluble hormones, the receptors are intracellular and for water-soluble hormones, the receptors are present on cell surface.

Answer to Problem 1IQ

Pictorial representation: Fig.1 represents the pathway of a water-soluble hormone and a lipid-soluble hormone.

Fig. 1: Pathway of a water-soluble hormone and a lipid-soluble hormone

Explanation of Solution

Water-soluble hormones bind to cell surface receptors of their target cells, which stimulate gene expression and cause cytoplasmic changes. They cannot travel inside the cells through the plasma membrane because of its insoluble nature in the lipid. Transfer of the extracellular chemical signal to intracellular response is termed as signal transduction. Peptide hormones act through signal transduction pathways. Once water-soluble hormones bind to their receptors, they activate transfer of cytoplasmic protein to the nucleus, leading to alteration in gene expression.

Lipid-soluble hormones cross the barrier of the plasma membrane and interact with receptors, which are present in the cytoplasm or nucleus. It results in the formation of the hormone­–receptor complex. The hormone receptors that bind to lipid-soluble hormone in their circulation are called as lipid-soluble hormone receptors. They are usually present in the cytoplasm or nucleus. The hormone–receptor complex is formed to initiate transcription by interaction with deoxyribonucleic acid (DNA).