Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? a. Enzymatic activity was proportional to the amount of calcium added to a cell-free extract. b. Receptor studies indicated that epinephrine was a ligand. c. Glycogen breakdown was observed only when epinephrine was administered to intact cells. d. Glycogen breakdown was observed only when epinephrine and glycogen phosphorylase were mixed.

Verified step by step guidance

1. Step 1: Understand the question. The question is asking about the observation that led Earl W. Sutherland to propose the concept of a second messenger in the action of epinephrine on liver cells.
2. Step 2: Recall what a second messenger is. In cell biology, a second messenger is a substance whose release within a cell is promoted by a hormone and that brings about a response from the cell.
3. Step 3: Review the given options. We need to find the option that suggests the involvement of a substance other than epinephrine itself in bringing about the cell's response.
4. Step 4: Evaluate the options. Option a is about calcium, which is not directly related to epinephrine's effect. Option b is about epinephrine being a ligand, which doesn't suggest the involvement of a second messenger. Option d is about the direct interaction between epinephrine and glycogen phosphorylase, which also doesn't suggest the involvement of a second messenger.
5. Step 5: Choose the correct answer. The correct answer is option c. Glycogen breakdown was observed only when epinephrine was administered to intact cells. This suggests that something within the intact cells, a second messenger, is necessary for the effect of epinephrine.

Key Concepts

Second Messengers

Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules (first messengers) like hormones. They play a crucial role in amplifying the signal from the first messenger, leading to a physiological response. In the case of epinephrine, the involvement of second messengers is essential for mediating its effects on target cells, such as liver cells.

Epinephrine and Glycogen Breakdown

Epinephrine, also known as adrenaline, is a hormone that triggers various physiological responses, including the breakdown of glycogen into glucose in liver cells. This process is vital for providing energy during stress or 'fight or flight' situations. Understanding how epinephrine interacts with liver cells helps clarify the mechanisms behind glycogenolysis and the role of second messengers in this pathway.

Receptor-Ligand Interaction

Receptor-ligand interactions are fundamental to cellular communication, where a ligand (such as epinephrine) binds to a specific receptor on the cell surface, initiating a cascade of intracellular events. This binding can activate various signaling pathways, including those involving second messengers. The observation of epinephrine as a ligand suggests that it triggers specific responses in target cells, leading to further investigation into the signaling mechanisms involved.