Question

Assertion: Thyroxine is lipid soluble hormone. Reason: Receptor for thyroxine is situated in cytoplasm.

Short answer

The assertion is correct; Thyroxine is a lipid-soluble hormone but the reason is incorrect. The receptor for thyroxine is located in the cell nucleus, not in the cytoplasm.

Step-by-step solution

Understanding Solubility of Thyroxine

Confirming whether thyroxine is lipid soluble or not. Thyroxine is indeed a lipid soluble hormone. It can move across the cell membrane into the cell due to its lipid solubility.

Identifying Receptor Location for Thyroxine

Now the location of the receptor for thyroxine should be determined. The receptors for thyroxine are not located in the cytoplasm. They are actually located in the nucleus of the cell. This is because they directly influence the DNA in the nucleus to modify the cell's function.

Conclusion

Hence, while the assertion about the lipid solubility of thyroxine is correct, the reason stating that its receptor is situated in the cytoplasm is incorrect. As a lipid soluble hormone, thyroxine's receptors are located in the cell nucleus, not the cytoplasm.

Key concepts

Lipid Soluble Hormones

Lipid soluble hormones, like Thyroxine, have the ability to easily pass through cell membranes. This is due to their unique biochemical properties. Unlike their water-soluble counterparts, they do not dissolve in the blood easily and typically bind to transport proteins in the bloodstream. Once they reach their target cells, their lipid solubility allows them to directly cross the phospholipid bilayer of the cell membrane.
This attribute enables them to move freely within the cell where they interact with their specific receptors. This movement is crucial for their function, as it influences cellular activity by directly entering target cells. Understanding the nature of these hormones helps clarify how they achieve their regulatory functions within the body.

Cell Receptors

Cell receptors are specialized proteins located on or within cells, which bind to specific hormones or other molecules. For lipid-soluble hormones like Thyroxine, their receptors are typically located inside the cell. This is different from water-soluble hormones, whose receptors are usually found on the cell surface.
These internal receptors for lipid-soluble hormones are generally found either in the cytoplasm or nucleus of the cell. Upon binding, the hormone-receptor complex undergoes a change that allows it to perform its function, such as activating or repressing genes. This process is crucial as it modulates various physiological functions, thereby maintaining homeostasis in the body.

Hormone Function

Hormones play critical roles in regulating a variety of bodily functions. Thyroxine, being a thyroid hormone, is particularly important for controlling metabolism, growth, and development. It does so by entering cells and interacting with their internal receptors. This interaction typically influences the expression of genes within the nucleus, which can lead to increased metabolic activity.
Because of its ability to modulate gene expression, Thyroxine has far-reaching effects on energy levels and overall metabolic rate. This function makes it an essential component in the body's ability to adapt to changes in energy demand and maintain optimal function of various organs and tissues.

Nucleic Receptors

Nuclear receptors are a class of proteins found within cells that are responsible for sensing steroid and thyroid hormones like Thyroxine. Once a hormone like Thyroxine enters a cell, it binds to these receptors in the nucleus. Here, the hormone-receptor complex acts as a transcription factor, directly influencing gene expression by turning certain genes on or off.
This ability to directly modify gene transcription is what sets nuclear receptors apart from other types of receptors. It allows for precise control over various physiological processes, such as metabolism, immune responses, and cell differentiation. Understanding the role of nuclear receptors helps illuminate how hormones can enact widespread changes in bodily function and contribute to maintaining homeostasis.