Question

List two hormones that work through the cAMP second messenger.

Short answer

Adrenaline (epinephrine) and glucagon.

Step-by-step solution

- Understand Second Messengers

Second messengers are molecules that relay signals received at receptors on the cell surface to target molecules inside the cell. Cyclic AMP (cAMP) is an important second messenger used by many hormones.

- Identify Hormones Using cAMP

Research and identify hormones that utilize the cAMP pathway for their signaling mechanism. These hormones often activate adenylyl cyclase, an enzyme that converts ATP to cyclic AMP.

- List Two Hormones

Common examples of hormones that work through the cAMP second messenger include adrenaline (epinephrine) and glucagon.

Key concepts

Second Messengers

In cellular biology, second messengers are crucial for transmitting signals from receptors on the cell surface to their subsequent targets within the cell. When a hormone binds to its receptor, it does not enter the cell directly.
Instead, it relies on intermediary molecules to propagate the signal. These intermediaries are termed 'second messengers'. They amplify the signal, ensuring that even a small number of hormone molecules can have a large effect. Examples of second messengers include cyclic AMP (cAMP), inositol triphosphate (IP3), and calcium ions (Ca²⁺).
Understanding the role of second messengers is key to grasping how cells respond to external signals and maintain homeostasis.

Cyclic AMP

Cyclic adenosine monophosphate (cAMP) is a pivotal second messenger involved in many biological processes. It is derived from ATP and acts as a signaling molecule within many different cells.
When a hormone like adrenaline binds to its receptor on the cell surface, it activates an enzyme called adenylyl cyclase, which then converts ATP to cAMP. The rise in cAMP levels leads to the activation of protein kinase A (PKA) and other downstream signaling pathways.
This cascade effect allows for a rapid and amplified cellular response. Thus, cAMP plays a significant role in processes such as energy balance, cell division, and the regulation of metabolic pathways.

Hormone Signaling Mechanisms

Hormones communicate messages through specific signaling mechanisms to ensure proper cell and organ function. For hormones that use cAMP as a second messenger, the sequence typically involves:

• Hormone binding to receptor on cell membrane.
• Activation of a G protein.
• Stimulation of adenylyl cyclase.
• Conversion of ATP to cAMP.
• Activation of PKA and other downstream effects.

This sequence allows cells to respond to external signals efficiently and precisely.
Importantly, different hormones can share the same signaling pathway, yet produce distinct physiological outcomes depending on the cell type and context.

Adenylyl Cyclase

Adenylyl cyclase is a critical enzyme in the cAMP signaling pathway. Located on the inner side of the cell membrane, it is activated by G proteins, which in turn are activated by hormone-receptor binding.
Once activated, adenylyl cyclase catalyzes the conversion of ATP to cAMP, thus increasing cAMP levels within the cell. This rise in cAMP activates protein kinase A (PKA), initiating a cascade of cellular events.
Given its central role in generating cAMP, adenylyl cyclase is vital for processes regulated by cAMP signaling such as energy metabolism, gene transcription, and memory formation.

Adrenaline

Adrenaline, also known as epinephrine, is a hormone and neurotransmitter involved in the fight-or-flight response. When adrenaline binds to its receptors on the surface of target cells, it typically activates the cAMP signaling pathway.
This activation leads to increased levels of cAMP in the cell, stimulating processes such as the breakdown of glycogen to glucose in the liver and the release of fatty acids in adipose tissue.
Through these actions, adrenaline helps to mobilize the body’s energy reserves, preparing it to respond to stressful situations quickly.

Glucagon

Glucagon is a hormone produced by the pancreas that plays a key role in blood glucose regulation. When blood sugar levels are low, glucagon is secreted and binds to its receptors on liver cells.
Similar to adrenaline, this binding activates the cAMP signaling pathway. Elevated levels of cAMP lead to the activation of enzymes involved in glycogen breakdown and glucose synthesis.
Thus, glucagon ensures that glucose is released into the bloodstream, maintaining blood sugar levels within a healthy range, especially during fasting or between meals.