Problem 3 - Campbell Biology

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

Step-by-Step Solution

Answer

Option (B) is correct because only target cells have intracellular receptors for aldosterone.

Step 1: Understand the Question

Determine why lipid-soluble molecules like aldosterone can cross the membranes of all cells but only affect target cells.

Step 2: Analyze Each Option

Evaluate each answer choice to see which best explains why aldosterone only affects target cells: (A) Evaluate if only target cells retain the appropriate DNA segments. (B) Evaluate if intracellular receptors are present only in target cells. (C) Evaluate if only target cells have enzymes that break down aldosterone. (D) Evaluate if only in target cells aldosterone initiates the phosphorylation cascade.

Step 3: Rule Out Incorrect Options

Review why options (A), (C), and (D) are incorrect: (A) All cells have the same DNA. (C) This does not explain selective response, as enzymes do not discriminate signal transduction. (D) This is an effect, not the initiating cause.

Step 4: Confirm the Correct Answer

Option (B) is correct because intracellular receptors, which aldosterone must bind to in order to exert an effect, are present only in target cells.

Key Concepts

lipid-soluble signaling molecules

Lipid-soluble signaling molecules like aldosterone play a crucial role in cellular communication. They can easily pass through the lipid bilayer of cell membranes due to their solubility in lipids.

These molecules can affect a wide range of physiological processes, such as metabolism, growth, and reproduction. Their lipid-soluble nature allows them to cross the membranes of all cells in the body. However, not all cells respond to these molecules. The response is highly specific, depending on the presence of intracellular receptors in certain cells.

To summarize:

• Lipid-soluble signaling molecules can cross cell membranes easily due to their lipid solubility.
• They impact various physiological processes.
• Not all cells respond to these molecules, making the communication highly targeted.

intracellular receptors

Intracellular receptors are specialized proteins located inside the cell, either in the cytoplasm or the nucleus. They are essential for lipid-soluble signaling molecules like aldosterone.

When lipid-soluble molecules like aldosterone enter a cell, they bind to these receptors to form a receptor-ligand complex. This complex can then move to the cell nucleus, where it can influence gene expression directly.

The specificity of the intracellular receptors is what makes only certain cells, called target cells, respond to the signaling molecules.

• Located inside the cell, often in the cytoplasm or nucleus.
• Bind with lipid-soluble signaling molecules to form a receptor-ligand complex.
• Affects gene expression directly.
• Only present in specific target cells.

target cells

Target cells are the specific cells that respond to signaling molecules like aldosterone. While all cells might come into contact with aldosterone, only target cells have the right intracellular receptors to bind with it.

This interaction between aldosterone and its receptors in target cells leads to specific physiological changes within those cells. For example, in the kidneys, aldosterone affects sodium and water balance by changing gene expression related to ion channels and transporters.

The presence of intracellular receptors in target cells is what makes these cells responsive to lipid-soluble signaling molecules.

• Have specific intracellular receptors to bind signaling molecules.
• Respond to these molecules with particular physiological changes.
• Example: Aldosterone affects kidney function by altering gene expression.

aldosterone

Aldosterone is a lipid-soluble signaling molecule that plays a significant role in regulating sodium and potassium balance in the body.

As a hormone, it is produced in the adrenal glands and travels through the bloodstream to reach its target cells, primarily in the kidneys. Once it enters the target cells, aldosterone binds to intracellular receptors, forming a receptor-ligand complex.

This complex then influences the expression of genes responsible for sodium and potassium transport, ultimately affecting the overall fluid balance in the body.

• Lipid-soluble hormone produced by adrenal glands.
• Regulates sodium and potassium balance.
• Travels through the bloodstream to target cells, mostly in the kidneys.
• Forms a receptor-ligand complex that influences gene expression.