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1. Overview Calcium (Ca²⁺) signaling is one of the most important intracellular signaling systems in eukaryotic cells. Ca²⁺ acts as a second messenger, translating extracellular or intracellular stimuli into cellular responses. Although intracellular free Ca²⁺ concentration is normally kept very low, transient increases in cytosolic Ca²⁺ can regulate: Central principle Stimulus → Ca²⁺ entry/release → transient rise in [Ca²⁺]ᵢ → Ca²⁺ sensor/protein → cellular response → Ca²⁺ removal 2. Why Ca²⁺ Is an Effective Second Messenger Ca²⁺ is particularly suitable as a signaling molecule because: The large concentration gradient provides a powerful driving force for Ca²⁺ movement into the cytosol. 3. Cellular Ca²⁺ Distribution ApproximateRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Receptor tyrosine kinases (RTKs) are a major family of cell-surface transmembrane receptors that convert extracellular signals into intracellular responses by activating protein tyrosine kinase activity. RTKs regulate: Important RTKs include receptors for: 2. Basic RTK Structure A typical RTK contains three major regions: Major components 3. Important Difference from GPCRs RTKs differ fundamentally from GPCRs. Feature GPCR RTK Transmembrane segments 7 Usually 1 Main signaling partner Heterotrimeric G protein Protein/adaptor signaling complexes Intrinsic kinase activity No Usually yes Major phosphorylation Various downstream proteins Tyrosine residues Major pathways cAMP, IP3/DAG RAS–MAPK, PI3K–AKT, PLCγ Typical function BroadRead More →