Description
This comprehensive academic presentation on signal transduction provides a detailed exploration of cellular communication mechanisms, receptor types, and associated pathways crucial for understanding molecular biology and disease processes. The material explains how cells coordinate through chemical signals, detailing extracellular receptors such as G protein-coupled receptors (GPCRs), receptor tyrosine kinases (RTKs), integrins, toll-like receptors, and ligand-gated ion channels, alongside intracellular receptors for hormones like steroids and thyroid hormones. Key signaling pathways, including cAMP-dependent and MAP kinase cascades, are outlined, with emphasis on their roles in regulating cell growth, differentiation, and immune responses. The presentation also highlights the relevance of signal transduction dysregulation in diseases, particularly cancer, where mutations in pathways involving RAS, JAK-STAT, and PI3K contribute to oncogenesis and drug resistance. This resource is essential for medical students, molecular biology trainees, and researchers in Zambia, offering structured, exam-focused content for mastering cellular signaling concepts within a tertiary medical education context. Download these detailed notes for thorough preparation and clinical insights.
What's inside
SIGNAL TRANSDUCTION JAMES KAPIYA 6TH YEAR MEDICAL STUDENT UNZA-SOM INTRODUCTION •In human body, numerous processes are required for coordinating individual cells to support the entire body. •At the cellular level, Sensing of environments and cell communication for coordination relies on signal transduction; modeling signal transduction systems as self-organizing allows one to explain how equilibria are maintained. • Many disease processes, such as diabetes and heart disease arise from defects or dysregulations in these pathways, highlighting the importance of these processes in human biology and medicine •Cell communication occurs through chemical signals and cellular receptors by either the •1)direct contact of molecules on two cells surfaces or the •2)release of a "chemical signal" recognized by another cell (near or far). •Hormones are carried by the circulatory systems to many sites. •Growth factors are released to act on nearby tissues •Ligands are signals that bind cell surface receptors or that can pass into the cell and bind an internal receptor. SIGNAL TRANSDUCTION •Any process occurring within cells that convert one kind of signal/stimulus into another type. •It also known as cell signaling in which the transmission of molecular signal from a cell's exterior to its interior. •Signal received by cells must be transmitted effectively into the cell to ensure an appropriate response. This step is initiated by cell-surface receptors which triggers a biochemical chain of events inside the cell, creating a response. •It is also defined as the ability of a cell to change behavior in response to a receptor-ligand interaction.(signal) •The ligand is the primary messenger and as the result of binding the receptor, other molecules or second messengers are produced within the target cell. •Second messengers relay the signal from one location to another (such as from plasma membrane to nucleus) leading to cascade of events/changes within a cell Pictorial • Messenger molecules may be amino acids, peptides, proteins, fatty acids, lipids, nucleosides or nucleotides. • Hydrophilic messengers bind to cell membrane receptors • Hydrophobic messengers bind to intracellular receptors which regulate expression of specific genes. • A ligand binds its receptor through a number of specific weak non-covalent bonds by fitting into a specific binding site or "pocket" • In situations where even low concentrations of a ligand will result in binding of most of the corresponding receptors, the receptor affinity is considered to be high. • Low receptor affinity occurs when a high concentration of the ligand is required for most receptors to be occupied. • The dissociation constant (Kd) is the concentration of ligand required to occupy one half of the total available receptors. • With prolonged exposure to a ligand cells often become desensitized. • Desensitization of the cell to a ligand depends upon receptor down-regulation. • Desensitization may lead to tolerance, a phenomenon that results in the loss of medicinal effectiveness of some medicines that are over prescribed. RECEPTORS • Receptors can be roughly divided into two major classes: intracellular receptors and extracellular receptors. 1. EXTRACELLULAR RECEPTORS •Extracellular receptors are integral transmembrane proteins and make up most receptors. •They span the plasma membrane of the cell, with one part of the receptor on the outside of the cell and the other on the inside. •Signal transduction occurs as a result of a ligand binding to the outside region of the receptor (the ligand does not pass through the membrane). Various Extracellular Receptors • G protein-coupled receptors • Receptors with Kinase activity. • Integrin receptors. • Toll gate receptors. • Ligand-gated ion channel receptors G PROTEIN-COUPLED RECEPTORS (GPCRs) Also known as seven-transmembrane domain receptors, 7TM receptors, heptahelical receptors, and G protein-linked receptors (GPLR). • These constitute a large protein family of receptors that sense molecules outside the cell and activate inside signal transduction pathways and, ultimately, cellular responses. • Coupling with G proteins, they are called seven-transmembrane receptors because they pass through the cell membrane seven times. • The ligands that bind and activate these receptors include light- sensitive compounds, odors, pheromones, hormones, and neurotransmitters, and vary in size from small molecules to peptides to large proteins. • G protein coupled receptors are involved in many diseases, and are also the target of approximately 40% of all modern medicinal drugs. • G proteins, also known as …
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