Question

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 downaldosterone.

(D) only in target cells is aldosterone able to initiate thephosphorylation cascade that turns genes on.

Short answer

(A) The statement “only target cells retain the appropriate DNA segments” is false.

(B) The statement “intracellular receptors are present only in target cells” is true.

(C) The statement “only target cells have enzymes that break down aldosterone” is false.

(D)The statement “only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on” is false.

Step-by-step solution

Step 1: Intracellular receptors

The receptor proteins are only found in the target cells in their cytoplasm and nucleus. For binding, these receptors signal molecules to cross the plasma membrane to reach them. So, these signaling molecules are small and hydrophobic. Their binding with the receptor can turn on or off the genes in the nucleus.

Explanation of option ‘(A)’

Lipid soluble compounds, like the steroid hormone aldosterone, can cross the plasma membrane of all cells but affect only target cells by intracellular binding receptors present inside them. So, the presence of these receptors is specific for binding with such hydrophobic molecules in the target cells.

DNA segments in all cells are similar and affected by the binding of these molecules with intracellular receptors.

Thus,target cells contain similar DNA segments to other cells.

Therefore, the given statement is false.

Explanation of option ‘(B)’

Target cells contain some intracellular receptors that make them specific for binding with lipid-soluble molecules like steroid hormones. For example, the hormone aldosterone travels through the blood and reaches each cell of the body but responds only in kidney cells because these cells contain receptor molecules for this hormone.

Thus,intracellular receptors have the primary role in giving specificity to the target cells for recognizing lipid-soluble molecules like steroid hormones.

Therefore, the given statement is true.

Explanation of option ‘(C)’

The target cells for aldosterone are kidney cells because they have intra-cellular receptors for this hormone. A hormone-receptor complex is formed, and it activates the genes present in the nucleus.

Thus,target cells have no specific enzymes to break the aldosterone.

Therefore, the given statement is false.

Explanation of option ‘(D)’

In target cells, hormones bind with the intracellular receptors present inside them, rather than the presence of a phosphorylation cascade that involves protein kinases.

Thus, target cells for steroid hormones like aldosterone do not have a phosphorylation cascade.

Therefore, the given statement is false.