Intercellular Signaling part 3

Summary

This transcript delves into cellular signaling mechanisms, focusing on cyclic AMP (cAMP) and calcium ions. It explores how the activation of adenylate cyclase converts ATP into cAMP, leading to the activation of protein kinase A (PKA). Additionally, it highlights the role of calcium ions as second messengers, their regulation by phospholipase C, and their impact on cellular processes like fertilization and enzyme activation. The script also discusses how calcium influences protein kinase C (PKC) and cam kinase, contributing to cellular memory and learning. Finally, it describes the termination of signaling pathways, ensuring controlled cellular responses.

Takeaways

• 😀 Adenosine monophosphate (AMP) is formed from ATP through the action of the enzyme adenylate cyclase, which is activated by certain proteins called G-proteins.
• 😀 Cyclic AMP (cAMP) plays a key role in cellular signaling by activating protein kinases like protein kinase A (PKA).
• 😀 PKA is activated when cAMP binds to its regulatory subunits, causing a structural change that releases its catalytic subunits, making them active.
• 😀 PKA activation triggers the activation of transcription factors such as CREB (cAMP response element-binding protein), influencing gene expression.
• 😀 Gene expression regulated by CREB involves target genes like somatostatin and corticotropin-releasing hormone, which impact hormone release and biological processes.
• 😀 Calcium ions serve as another important second messenger in cellular signaling, influencing processes like fertilization, development, and gene expression.
• 😀 Calcium influx during fertilization in sea star eggs prevents polyspermy, which ensures that only one sperm enters the egg.
• 😀 Calcium ion concentration within cells is regulated by transporters, which help maintain low cytosolic calcium levels compared to the extracellular space or intracellular compartments.
• 😀 Phospholipase C, found in sperm cells, helps generate inositol trisphosphate (IP3), which triggers calcium release from intracellular stores like the endoplasmic reticulum.
• 😀 Several types of calcium channels, such as IP3 receptors and ryanodine receptors, regulate calcium flow within cells, essential for maintaining cellular processes like muscle contraction and neurotransmission.
• 😀 Calmodulin is a calcium-binding protein that activates enzymes like calmodulin-dependent kinase (CaMK), which is involved in learning and memory processes by modulating cellular activity.

Q & A

What is the role of adenosine monophosphate (AMP) in cellular processes?

Adenosine monophosphate (AMP) plays a crucial role in various cellular processes by acting as a second messenger, which is formed from ATP by the enzyme adenylate cyclase. It helps in regulating various signaling pathways and activating proteins like protein kinase A (PKA).

How does the activation of protein kinase A (PKA) occur?

The activation of PKA occurs when cyclic AMP (cAMP) binds to the regulatory subunits of PKA, causing a conformational change that results in the release of the catalytic subunits. These catalytic subunits then become active and can initiate cellular processes.

What is the role of the CREB transcription factor in gene expression?

CREB (cAMP response element-binding protein) is a transcription factor activated by PKA. Once activated, CREB binds to DNA sequences called cAMP response elements (CRE), promoting the expression of genes involved in processes like cell growth and metabolism.

What are the main targets of CREB activation?

One of the main targets of CREB activation is the somatostatin gene, which regulates the secretion of growth hormone. Another target is the corticotropin-releasing hormone gene, which is involved in the regulation of cortisol secretion.

What is the role of calcium ions in cellular signaling?

Calcium ions act as another important second messenger in cellular signaling. They regulate various processes such as fertilization, cell development, and gene expression by triggering enzymes and altering cellular activities.

How does calcium concentration change during fertilization in sea stars?

During fertilization in sea stars, calcium ions increase in concentration in response to the entry of sperm. This change in calcium levels helps prevent polyspermy (entry of multiple sperm) and initiates the development of the embryo.

What is the role of phospholipase C in calcium signaling?

Phospholipase C is an enzyme that breaks down phosphatidylinositol in the membrane, producing inositol trisphosphate (IP3). IP3 then activates calcium channels on the endoplasmic reticulum, leading to the release of calcium ions into the cytosol.

What are the key transporters involved in regulating calcium levels inside the cell?

Key transporters involved in calcium regulation include antiporters like Na+/Ca2+ exchangers and uniporters that pump calcium into or out of the endoplasmic reticulum or mitochondria. These transporters help maintain low cytosolic calcium concentrations.

How does calmodulin interact with calcium in cellular signaling?

Calmodulin is a calcium-binding protein that, upon binding to calcium ions, undergoes a conformational change and activates various enzymes like calmodulin-dependent protein kinases. This activation plays a role in processes such as memory and learning.

How is cellular signaling terminated when no longer needed?

Cellular signaling is terminated by processes such as the phosphorylation of G-protein-coupled receptors (GPCRs). This prevents further activation of signaling pathways, effectively shutting down the cellular response once it is no longer needed.