Chapter 46, Problem 1TYK

Summary Introduction

Introduction:

Hormones are the chemical compounds found in plants and animals with different chemical and structural formulas. In animals, hormones are secreted by either endocrine or exocrine glands. These are present at different locations. Steroid hormones are of two types in animals—sex steroids and corticosteroids. Steroid hormones are long-term hormones: they are in the system for a longer period of time as compared to the other kinds of hormones.

Answer to Problem 1TYK

Correct answer:

Steroid hormones being lipid soluble can easily pass through plasma membrane (a lipid bilayer). The receptors for lipid soluble hormones exist inside the cell.

Explanation of Solution

Explanation/Justification for the correct answer:

Option (a) is given as steroid hormones being lipid soluble can cross the plasma membrane. Animal hormones are mostly amino acid derivatives, steroids, or polypeptides. Steroid hormones belong to the category of lipid-soluble hormones. They have a lipid nature, which makes it easier for them to be transported across the cell membranes and bind to receptors located in the membranes of target cells. Hence, option (a) is correct.

Explanation for incorrect answer:

Option (b) is given as that amino acid derived and polypeptide hormones are longer lived and have a greater signal amplification. However, it is the steroid hormone, which lasts longer in the circulation as compared to the given hormones in the option. So, it is a wrong answer.

Option (c) is given as that complexity of polypeptide hormones is more than steroid hormones and they induce permanent change. Polypeptide or protein hormones are short-acting in nature. Steroid hormones have a longer life period than polypeptide hormones. The complexity does not define the effect of any hormone. The effects of these hormones are not permanent. So, it is a wrong answer.

Option (d) is given as that it is the steroid hormones alone can bind to the receptors in cell surface. Polypeptide hormones are the ones that usually bind to the cell surface. Polypeptide hormones after binding to the cell surface receptors initiate a cascade of secondary reactions. The receptors for steroid hormones can be in the cytoplasm, cell membrane, or intranuclear. So, it is a wrong answer.

Hence, options (b), (c), and (d) are incorrect.

Conclusion

Steroid hormones are known to act by binding to intracellular receptors. These receptors can be inside the nucleus also. The ability to cross plasma membrane is due to hydrophobic nature of both steroid hormones and plasma membrane.