Problem 1 - Anatomy and Physiology of Animals

Question

Visit this link (http://openstaxcollege.org/l/ hormonebind) to watch an animation of the events that occur when a hormone binds to a cell membrane receptor. What is the secondary messenger made by adenylyl cyclase during the activation of liver cells by epinephrine?

Step-by-Step Solution

Answer

cAMP is the secondary messenger produced by adenylyl cyclase.

Step 1: Understand the Question

The problem requires us to identify the secondary messenger that is produced when a hormone, specifically epinephrine, binds to a liver cell membrane receptor and activates adenylyl cyclase.

Step 2: Review Hormone Activation Mechanism

When epinephrine binds to its receptor on the liver cell membrane, it activates a G protein. This activation leads to the stimulation of adenylyl cyclase, an enzyme located on the inside of the cell membrane.

Step 3: Identify Secondary Messenger

Adenylyl cyclase converts ATP to cyclic AMP (cAMP). The cAMP functions as a secondary messenger, transmitting the signal initiated by the hormone binding into the cell to exert a physiological response.

Key Concepts

cyclic AMP (cAMP)

Cyclic AMP, or cAMP, is a crucial "secondary messenger" in many biological processes. Imagine it as a messenger inside the cell that carries the instructions given by hormones. In the context of hormone-receptor interaction, once a hormone like epinephrine attaches to a receptor on a liver cell, cAMP plays a key role in conveying that signal within the cell.

When a hormone binds and triggers this cascade, adenylyl cyclase, an enzyme, converts ATP (adenosine triphosphate) into cAMP. This transformation is critical because cAMP then activates other proteins in the cell, particularly protein kinase A (PKA).

• Acts as a signal carrier within cells
  
• Produced from ATP by the action of adenylyl cyclase
  
• Activates protein kinase A, among other pathways.

cAMP's ability to amplify signals means it helps the cell respond appropriately to signals it receives from hormones, leading to necessary reactions such as glycogen breakdown in liver cells.

adenylyl cyclase

Adenylyl cyclase is an important enzyme located inside the cell membrane. It is like a "switch" that turns ATP into cAMP, the secondary messenger. When a hormone like epinephrine binds to a receptor on the cell surface, adenylyl cyclase is activated through a series of steps.

The primary function of adenylyl cyclase is to catalyze the conversion of ATP, a high-energy molecule, into cAMP. The process is crucial because without this enzyme, the signal from the hormone would not be passed on into the cell efficiently.

• Sits on the inside of the cell membrane
  
• Converts ATP to cAMP
  
• Activated by G proteins when a hormone receptor is engaged

In essence, adenylyl cyclase bridges the message from a cell's exterior to its interior, thereby initiating the necessary cellular response.

G protein activation

G protein activation is a pivotal part of how cells communicate in response to external signals. These proteins are located inside the cell and are activated when a hormone, such as epinephrine, binds to its corresponding receptor on the cell surface.

Think of G proteins as molecular "on-off switches" that transmit signals from receptors to enzymes and other proteins inside the cell. When a hormone-receptor binding triggers a G protein, it changes its structure, enabling it to activate adenylyl cyclase.

• Acts as a signal mediator between the receptor and adenylyl cyclase
  
• Changes structure upon activation
  
• Allows the production of secondary messengers like cAMP

Thanks to G protein activation, cells can respond appropriately to external stimuli by propagating the signal internally, ultimately influencing cellular functions such as metabolism, secretion, and growth.