Chapter 17 Water Soluble Hormone Action

Summary

This video explains how hydrophilic hormones communicate with cells via a signaling pathway. Since they cannot cross the cell membrane, they bind to receptors on the cell's surface, activating a G-protein. The G-protein then activates adenylate cyclase, which produces cyclic AMP (cAMP), the second messenger. cAMP triggers protein kinases, which phosphorylate enzymes to alter cellular activity. For example, glucagon raises blood sugar by stimulating glycogen breakdown. The process is terminated by phosphodiesterase, which deactivates cAMP, ensuring the response is temporary and controlled.

Takeaways

• 😀 Hormones are chemical messengers that regulate cellular activities by binding to specific receptors.
• 😀 Hydrophilic (water-soluble) hormones cannot cross the cell membrane and must bind to receptors on the cell surface.
• 😀 These hormone receptors are transmembrane proteins embedded in the cell membrane.
• 😀 When a hormone binds to its receptor, it activates a series of intracellular reactions, leading to the desired cellular effect.
• 😀 The hormone itself is called the 'first messenger,' and it triggers the production of a 'second messenger' inside the cell.
• 😀 A key second messenger in this process is cyclic AMP (cAMP), which is formed from ATP by the enzyme adenylate cyclase.
• 😀 cAMP activates protein kinases (e.g., protein kinase A), which add phosphate groups to other proteins in a process called phosphorylation.
• 😀 Phosphorylation can activate or deactivate enzymes, influencing various metabolic pathways within the cell.
• 😀 An example of this process is glucagon, a hormone that increases blood sugar by promoting glycogen breakdown in the liver.
• 😀 The activity of cAMP is regulated by phosphodiesterase, which deactivates cAMP to prevent continuous signaling in the absence of the hormone.

Q & A

What are hormones and how do they function in the body?

Hormones are chemical messengers sent by one cell to another to trigger specific actions. They regulate various bodily functions by binding to receptors on target cells, signaling them to act or stop acting.

Why can't hydrophilic or water-soluble hormones cross the cell membrane?

Hydrophilic or water-soluble hormones cannot cross the phospholipid bilayer of the cell membrane because they are not able to pass through the lipid layer, which acts as a barrier to water-soluble substances.

Where are the receptors for hydrophilic hormones located?

The receptors for hydrophilic hormones are located on the cell membrane as transmembrane proteins. These proteins span the cell membrane to facilitate communication between the hormone and the inside of the cell.

What role do second messengers play in hormone signaling?

Second messengers, such as cyclic AMP (cAMP), are molecules inside the cell that relay signals from the hormone-receptor complex. They help initiate a cascade of reactions that result in the desired cellular response.

How is a G-protein involved in hormone signaling?

When a hormone binds to its receptor, it activates a G-protein on the cytosol side of the plasma membrane. This G-protein then triggers further downstream reactions, including the activation of enzymes like adenylate cyclase.

What is the function of adenylate cyclase in the signaling process?

Adenylate cyclase is an enzyme that catalyzes the conversion of ATP into cyclic AMP (cAMP), which acts as a second messenger in the signaling pathway.

What is cyclic AMP and how does it affect the cell?

Cyclic AMP (cAMP) is a second messenger produced by adenylate cyclase. It activates protein kinases, which phosphorylate other enzymes, thereby regulating various cellular processes such as metabolism.

What is the role of protein kinase A in hormone signaling?

Protein kinase A (PKA) is an enzyme that gets activated by cAMP. It adds phosphate groups to other enzymes in a process called phosphorylation, which either activates or deactivates these enzymes to produce the desired cellular effects.

How does glucagon influence blood sugar levels?

Glucagon raises blood sugar levels by activating enzymes that break down glycogen (the storage form of glucose) into glucose, which is then released into the bloodstream.

Why is phosphodiesterase important in regulating hormone signaling?

Phosphodiesterase inactivates cyclic AMP (cAMP) to ensure that the hormone signaling process does not continue indefinitely. It breaks down cAMP, stopping the cascade of reactions once the hormone is no longer present.