Cell Signalling Flashcards
Q1: What is the purpose of cell signaling in multicellular organisms?
Development, homeostasis, immune defense, and prevention of disorders.
What are the four types of signaling and their characteristics?
Endocrine: Hormones released into the bloodstream to distant target cells.
• Paracrine: Local mediators diffuse to nearby target cells.
• Neuronal: Action potentials transfer signals.
• Contact-dependent: Signal molecules in the signaling cell membrane interact with receptors on adjacent target cells.
What are examples of signaling factors?
Hormones, growth factors, metabolic regulators, migratory cues, cell death factors, neurotransmitters, and developmental patterning factors.
Why are receptors necessary for signaling?
They recognize hydrophilic signal molecules to trigger cascades in the target cell.
What are the properties of receptors?
They bind ligands with high selectivity and affinity.
How do intracellular receptors function?
Hydrophobic signal molecules diffuse into the cell and bind to receptors in the cytoplasm or nucleus, e.g., transcription factors.
What are the major membrane receptor families?
Ion Channels: Voltage-gated or neurotransmitter-gated.
- Enzyme Receptors: Often initiate phosphorylation cascades.
- GPCRs: 7 transmembrane domains with extracellular N-terminus and intracellular C-terminus.
How do GPCRs initiate signaling?
Signal binds to receptor → conformational change.
- Heterotrimeric G-protein dissociates:
• Gα exchanges GDP for GTP.
• Gα-GTP and Gβγ subunits activate downstream signaling.
How is GPCR signaling terminated?
Gα hydrolyzes GTP to GDP, and the G-protein re-associates to terminate the signal.
What is a second messenger, and how does cAMP function?
Second messengers amplify the primary signal.
• cAMP: Generated from ATP, activates Protein Kinase A (PKA), which phosphorylates proteins on serine and threonine residues.
How does Protein Kinase C (PKC) function?
PKC is activated by phospholipase C in a cascade, phosphorylating target proteins to regulate cellular processes.
How do β-adrenergic and α1-adrenergic receptors differ?
β-adrenergic (striated muscle): Activated by Gs protein for gluconeogenesis and lipolysis.
• α1-adrenergic (smooth muscle): Activated by Gq protein for smooth muscle contraction.
