Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because a. only target cells retain the appropriate DNA segments. b. intracellular receptors are present only in target cells. c. only target cells have enzymes that break down aldosterone. d. only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on.

Verified step by step guidance

1. Understand the nature of lipid-soluble signaling molecules: Lipid-soluble molecules like aldosterone can diffuse directly through the lipid bilayer of cell membranes due to their hydrophobic nature.
2. Recognize the role of intracellular receptors: Once inside the cell, lipid-soluble signaling molecules bind to specific intracellular receptors that are present in the cytoplasm or nucleus.
3. Identify the specificity of receptor presence: The presence of these specific receptors varies from cell to cell. Only target cells contain these specific receptors that can bind to the signaling molecule like aldosterone.
4. Connect receptor-signal complex to gene expression: Upon binding to the signaling molecule, the receptor-signal complex translocates to the nucleus where it can directly influence gene expression by acting as a transcription factor.
5. Conclude the correct answer: Since the presence of intracellular receptors that can bind to aldosterone and influence gene expression is unique to target cells, the correct answer is 'b. intracellular receptors are present only in target cells.'

Key Concepts

Lipid-Soluble Signaling Molecules

Lipid-soluble signaling molecules, like aldosterone, can easily cross cell membranes due to their hydrophobic nature. Once inside the cell, they bind to specific intracellular receptors, which then translocate to the nucleus to influence gene expression. This mechanism is crucial for regulating various physiological processes, including metabolism and immune response.

Intracellular Receptors

Intracellular receptors are proteins located within the cell that specifically bind to signaling molecules that have crossed the cell membrane. These receptors are essential for the action of lipid-soluble hormones, as they initiate a cascade of events leading to changes in gene expression. The presence of these receptors in target cells is what allows them to respond to specific hormones like aldosterone.

Phosphorylation Cascade

A phosphorylation cascade is a series of biochemical events where one enzyme activates another through the addition of phosphate groups, often leading to a significant cellular response. In the context of aldosterone, this cascade can activate transcription factors that turn on specific genes, ultimately resulting in physiological changes. This process is vital for the regulation of various cellular functions and responses.