Recording-2025-02-10T21:15:25.439Z

Cell Signaling Overview

• Cell signaling involves the release of signaling molecules that convey information to target cells.

• When a cell releases a signaling molecule that affects itself, this is known as autocrine signaling.

Types of Ligands

• Ligands are molecules that bind to specific receptors to elicit a response and can include:

  • Growth Factors: Proteins that stimulate cell growth and division.

  • Hormones: Chemical messengers that regulate various physiological processes.

  • Neurotransmitters: Chemicals that transmit signals across a synapse from one neuron to another.

Types of Receptors

• In this course, we will focus on four main types of receptors:

  • G Protein-coupled Receptors (GPCRs)

  • Tyrosine Kinase Receptors

  • Ion Channel Receptors

  • Intracellular Receptors

G Protein-coupled Receptors (GPCRs)

• GPCRs are complex proteins that span the cell membrane multiple times, typically seven times.

• Their structure includes:

  • Alpha Helices: Formed by hydrophobic amino acids that interact with the lipid bilayer of the membrane.

  • Hydrophobic and Hydrophilic Regions: The arrangement allows for interaction with the membrane and signaling molecules.

Activation of GPCRs

• When a ligand binds to a GPCR, it activates the receptor and promotes a conformational change.

• G Protein Functionality:

  • G proteins are inactive when bound to GDP.

  • Upon ligand binding, GDP is exchanged for GTP, activating the G protein.

Signaling Cascade via GPCRs

1. Activation of G Protein: The ligand-promoted conformation of the GPCR leads to the activation of the G protein.

2. G Protein Activation:

   • The GTP-bound form of the G protein interacts with and activates target enzymes (e.g., adenylyl cyclase).

3. Production of Second Messengers:

   • Adenylyl cyclase converts ATP into cyclic AMP (cAMP), which serves as a secondary messenger.

4. Activation of Protein Kinase:

   • cAMP activates Protein Kinase A (PKA), which initiates a cascade of further reactions.

Example of GPCR Functionality

• Adrenaline Release: Upon danger (e.g., camping scenario where one sees a bear), adrenaline is released:

  • It binds to GPCRs in liver cells.

  • The signaling pathway activates the conversion of glycogen into glucose, increasing blood sugar levels and providing energy for muscular response.

  • The process illustrates the importance of GPCRs in responding to physiological stimuli.

Importance of GPCR Signaling

• GPCRs are crucial for various physiological responses, including metabolism, sensory perception, and immune response.

• The ability to switch signaling on and off efficiently is vital for maintaining homeostasis in the body.