Question

How do steroid hormones induce a signaling cascade?

A) By binding to intracellular receptors and directly altering gene expression.
B) By binding to cell surface receptors and activating intracellular signaling pathways.
C) By inhibiting enzyme activity in the cytoplasm.
D) By promoting the formation of cyclic AMP (cAMP).

Answer 1

Steroid hormones induce a signaling cascade A. by binding to intracellular receptors and directly altering gene expression.

Step-by-step explanation:

Unlike water-soluble hormones, which bind to cell surface receptors and activate secondary messengers, steroid hormones are lipid-soluble and can easily cross the cell membrane to interact with intracellular receptor proteins. This receptor-hormone complex then enters the nucleus and directly alters gene expression, leading to the production of specific proteins.

For example, in response to cortisol, a steroid hormone secreted by the adrenal cortex, cortisol binds to glucocorticoid receptors on target cells. This binding causes conformational changes in the receptor, exposing a nuclear localization signal, which allows the receptor-hormone complex to enter the nucleus. In the nucleus, the complex can bind to specific DNA sequences called hormone response elements (HREs) and either enhance or repress gene transcription. This ultimately alters the expression of target genes, leading to physiological responses.

Therefore, steroid hormones induce a signaling cascade by binding to intracellular receptors and directly altering gene expression (Option A).

Answer 2

Steroid hormones initiate signaling by binding to intracellular receptors, forming a complex that directly alters gene expression. They can regulate gene transcription and modify cell structure and function by affecting protein synthesis. The complexity of hormone receptors and signaling pathways reflects the diverse mechanisms of hormone action in cells.

Step-by-step explanation:

Steroid hormones induce a signaling cascade by binding to intracellular receptors which are either in the cytoplasm or nucleus of the target cell. The correct answer to how steroid hormones induce a signaling cascade is A) By binding to intracellular receptors and directly altering gene expression. Once inside the cell, the hormones diffuse across the lipid bilayer and adhere to these receptors forming a hormone-receptor complex. This complex acts as a transcription regulator, influencing the synthesis of mRNA molecules of specific genes and thereby regulating the production of proteins that can alter the cell's structure or catalyze chemical reactions.

Lipid-derived hormones that are not steroids, including vitamin D and thyroxin, also bind to intracellular receptors to regulate gene transcription. In contrast, amino acid-derived hormones and polypeptide hormones, which are not lipid-soluble, bind to cell surface receptors and act indirectly by triggering intracellular signaling pathways that lead to cellular responses, illustrating the complex nature of hormone receptors.