Question

Steroid hormones are steroids that: I. have specific high-affinity receptors. II. travel in the bloodstream from endocrine glands to distant sites. III. affect gene transcription by binding directly to DNA (A) I only (B) III only (C) I and II only (D) I and III only

Short answer

The correct answer is (C) I and II only.

Step-by-step solution

Understand the Characteristics of Steroid Hormones

Steroid hormones are a type of hormone that can pass through cell membranes because they are lipid-soluble. They typically have specific high-affinity receptors, travel through the bloodstream from endocrine glands to distant sites, and their primary mode of action involves affecting gene transcription.

Evaluate Statement I

Statement I mentions that steroid hormones have specific high-affinity receptors. This is true, as steroid hormones bind to intracellular receptors with high specificity and affinity.

Evaluate Statement II

Statement II states that steroid hormones travel in the bloodstream from endocrine glands to distant sites. This is correct because steroid hormones are released by endocrine glands and circulate through the bloodstream to reach target tissues or organs.

Evaluate Statement III

Statement III asserts that steroid hormones affect gene transcription by binding directly to DNA. This is incorrect. Steroid hormones bind to their receptors, and the hormone-receptor complex then binds to DNA to affect gene transcription.

Determine the Correct Answer

Based on the evaluations: I and II are correct, while III is incorrect. Therefore, the correct choice is (C) I and II only.

Key concepts

Endocrine System

The endocrine system is a network of glands that produce and release hormones to regulate various body functions. Unlike the nervous system, which uses electrical signals, the endocrine system relies on chemical messengers known as hormones. These hormones travel through the bloodstream to target cells and organs.

Central to the endocrine system are the endocrine glands, such as the pituitary gland, thyroid gland, adrenal glands, and endocrine pancreas. These glands release hormones into the bloodstream, allowing them to reach distant parts of the body.

The endocrine system plays a critical role in growth and development, metabolism, and maintaining homeostasis. Through its hormones, it orchestrates a wide range of physiological activities, ensuring the body's internal environment remains stable and balanced.

High-Affinity Receptors

High-affinity receptors are specialized proteins located typically on the cell membrane or within the cell that bind to hormones with a high degree of specificity. This tight binding ensures that even low concentrations of hormones can exert their effects by activating these receptors.

In the case of steroid hormones, these receptors are found within the cell's cytoplasm or nucleus. When a steroid hormone enters a cell, it binds to its specific high-affinity receptor. This binding is so precise that each receptor will only interact with its corresponding hormone.

Once the hormone binds to its high-affinity receptor, the complex undergoes a conformational change, activating it. This hormone-receptor complex can then move into the nucleus to interact with DNA or other cellular components, triggering responses that regulate various cellular functions.

Gene Transcription Regulation

Gene transcription regulation is the process by which cells control the conversion of DNA to RNA, dictating which genes are expressed at any given time. This regulation is critical for maintaining cellular function, growth, and adaptation to varying conditions.

Steroid hormones play an essential role in gene transcription regulation. After a steroid hormone binds to its high-affinity receptor, the resulting hormone-receptor complex translocates to the cell nucleus. There, it binds to specific DNA sequences known as response elements.

By attaching to these response elements, the hormone-receptor complex can either promote or inhibit the transcription of particular genes. This regulation of gene transcription is a key mechanism by which steroid hormones influence cellular processes such as metabolism, growth, and differentiation.

Lipid-Soluble Hormones

Lipid-soluble hormones, such as steroid hormones, can easily pass through the lipid bilayer of cell membranes due to their solubility in lipids. This characteristic sets them apart from water-soluble hormones, which cannot diffuse through cell membranes and must bind to surface receptors.

Because they are lipid-soluble, steroid hormones like cortisol, estrogen, and testosterone enter cells by diffusing across the cell membrane. Inside the cell, they bind to intracellular high-affinity receptors, forming a hormone-receptor complex.

This complex can then travel into the cell's nucleus, where it influences gene transcription by binding to specific DNA sequences. This direct involvement in gene transcription allows lipid-soluble hormones to exert long-lasting and profound effects on cellular activities and overall physiological processes.