Question

Which hormone receptors are present in cytoplasm of target cell? (a) Thyroxin (b) Oestrogen (c) Insulin (d) All

Short answer

Thyroxin and Oestrogen have receptors in the cytoplasm of a target cell, not Insulin. Therefore (d) 'All' is the incorrect option.

Step-by-step solution

Identifying the Nature and Action of Hormones

The nature and action of hormones determine their localization in the cells. There are two types of hormones based on their nature: Protein Hormones and Steroid Hormones. The protein hormones are water-soluble and thus can't pass through the cell membrane, so their receptors are located on cell surface. The steroid hormones are fat-soluble, hence can easily pass through the cell membrane and their receptors are located inside the cell, in cytoplasm or nucleus.

Classifying Given Hormones

With the understanding from the previous step, one would classify the given hormones. (a) Thyroxin: This is a hormone produced by the thyroid gland. It is lipid soluble, and thus its receptors are found inside cells, in the nucleus, near regions of DNA that control the activation and deactivation of genes.(b) Oestrogen: This is a type of steroid hormone, which means it is fat-soluble so it can pass through the cell membrane. Oestrogen receptors are located in the nucleus but can also be found in the cytoplasm.(c) Insulin: This is a peptide hormone, which is water-soluble. Its receptors are located on the surface of cells. It cannot pass through the cell membrane to reach the cytoplasm.

Selecting Correct Answer

From the classification, it can be seen that of the given hormones, Thyroxin and Oestrogen have receptors that can be found in the cytoplasm of target cells, but not Insulin. Therefore the answer isn't 'All'. However, the question asks for hormones with receptors in the cytoplasm, not specifically only those. Therefore both Thyroxin and Oestrogen have receptors present in the cytoplasm of a target cell.

Key concepts

Cytoplasm

The cytoplasm is a gel-like substance found within the cell, surrounded by the cell membrane. It plays several crucial roles in cellular functions. This is the arena where most of the cellular activities occur, including metabolic pathways and signaling.

Receptors located here, such as those for certain lipid-soluble hormones, can directly influence the cell's activities. These receptors can move about within the cytoplasm, interacting with various cellular components.

• Provides a medium for biochemical reactions
• Facilitates transport within the cell
• Supports cellular structures like organelles

Understanding the role cytoplasm plays can help explain how certain hormone receptors are positioned for effective cellular communication.

Steroid Hormones

Steroid hormones are lipid-soluble molecules made from cholesterol. Due to their solubility in fats, they can easily pass through cellular membranes, unlike water-soluble hormones that need a receptor on the cell surface. Once inside the cell, these hormones often bind to receptors in the cytoplasm or nucleus.

Upon binding, they may alter gene expression by interacting with specific DNA sites. This can lead to significant but gradual changes in the target cell.

• Key steroid hormones include estrogen, testosterone, cortisol, and progesterone.
• They can influence functions such as metabolism, immune response, and sexual characteristics.
• Their ability to cross cell membranes allows them to modulate complex cell functions directly.

Their action can be both widespread and profound, demonstrating their integral role in maintaining physiological balance.

Protein Hormones

Protein hormones, unlike steroid hormones, are not lipid-soluble, and therefore cannot cross cell membranes directly. Instead, they depend on receptors located on the cell membrane's surface to initiate their action. These receptors are specific sites that trigger cellular responses when the hormone binds to them.

The binding often activates a secondary messenger system inside the cell, leading to a cascade of intracellular reactions.

• Common protein hormones include insulin, growth hormone, and follicle-stimulating hormone (FSH).
• This mechanism allows for a quick response to changes in the body’s environment.
• They primarily regulate processes like metabolism, growth, and energy balance.

Due to their mechanisms, protein hormones are crucial in real-time physiological regulation.

Cell Membrane

The cell membrane, or plasma membrane, is the protective barrier that surrounds the cell. It is primarily composed of a lipid bilayer with embedded proteins that control the movement of substances in and out of the cell.

Its selective permeability is crucial for maintaining homeostasis. In hormone signaling, the cell membrane acts as the first point of contact for protein hormones.

• Functions as a gateway for communication with the external environment.
• Contains receptor sites for the binding of specific hormones.
• Maintains the cell's structural integrity while allowing essential substances to pass.

Understanding the dynamics of the cell membrane is vital for grasping how hormones interact with target cells.

Thyroxin

Thyroxin is a vital hormone produced by the thyroid gland, primarily responsible for regulating metabolism. It is a lipid-soluble hormone, enabling it to traverse the cell membrane and act inside cells. Unlike most steroid hormones, thyroxin exerts its influence predominantly within the nucleus rather than the cytoplasm.

It directly affects DNA activity by modulating gene expression, thus influencing protein synthesis and metabolic processes.

• Essential in growth and development.
• Regulates the body's metabolic rate, influencing how energy is used.
• Helps maintain heart function, digestive health, and more.

Thyroxin’s ability to penetrate cells and command intricate genetic functions underscores its critical role in comprehensive physiological regulation.