Cell junctions and extracellular matrix

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Matrix metalloproteinases (MMPs) are a family of zinc-dependent proteolytic enzymes that cleave extracellular-matrix (ECM) proteins and other extracellular or cell-associated substrates. They are major regulators of: MMPs are not simply “matrix-destroying enzymes”; they are regulated molecular remodeling enzymes that alter the biochemical and mechanical information contained within the ECM. 2. Basic Reaction At a simplified level: MMP-mediated cleavage can therefore alter both structure and cell signaling. 3. Why Are They Called Metalloproteinases? The term has three components: Matrix Many substrates are components of the extracellular matrix. Metallo Their catalytic activity requires a metal ion, primarilyRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Extracellular matrix (ECM) remodeling is the continuous, regulated process of degradation, modification, synthesis, reorganization, and mechanical restructuring of extracellular-matrix components. It allows tissues to change their: ECM remodeling is not simply ECM degradation; it is a dynamic balance between matrix deposition, degradation, cross-linking, reorganization, and cell-mediated mechanical forces. 2. Major Components of the ECM The ECM consists broadly of: Fibrous proteins Adhesive glycoproteins Proteoglycans and glycosaminoglycans 3. Why Is ECM Remodeling Necessary? ECM remodeling is required for: It also contributes to pathological processes such as: 4. Basic Concept The ECM exists in a dynamic equilibrium.Read More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Laminins are large, multifunctional extracellular matrix glycoproteins that are major structural and signaling components of basement membranes. They regulate: Laminins are major basement-membrane organizers that connect extracellular matrix architecture with cell-surface receptors and intracellular signaling. 2. Basic Structure Laminins are heterotrimeric glycoproteins composed of three genetically distinct chains: These chains associate to form a characteristic cross-shaped molecule. A laminin molecule therefore contains: 1 α + 1 β + 1 γ chain 3. Laminin Gene Families Humans possess multiple laminin chain genes: These can combine to form numerous laminin heterotrimers. Examples: The numbering indicates: αβγ chainRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Fibronectin (FN) is a large, multifunctional extracellular matrix glycoprotein that plays a central role in: Fibronectin acts as a molecular bridge between cells and the extracellular matrix. Fibronectin links ECM components such as collagen to cell-surface integrins, thereby connecting extracellular matrix organization with intracellular cytoskeletal signaling. 2. Basic Structure Fibronectin is composed of two similar polypeptide subunits linked near their C-termini by disulfide bonds. It is therefore a disulfide-linked dimer. Each subunit contains multiple functional domains. 3. Fibronectin as a Modular Protein Fibronectin is a modular multidomain protein. It contains repeating structural modules known as:Read More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Collagen is the major structural protein of the extracellular matrix (ECM) and is the most abundant protein in the human body. It provides: Collagen is particularly important in: Collagen is not simply a structural scaffold; it is a dynamic signaling and mechanobiological component of the extracellular matrix. 2. Basic Molecular Organization The fundamental structural unit of fibrillar collagen is the triple helix. It consists of three polypeptide α-chains wound around each other. Each chain has a characteristic repeating sequence: Gly–X–Y where: 3. Why Glycine Is Essential The repeating sequence is approximately: Gly–X–Y–Gly–X–Y–… Glycine is theRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Integrins are heterodimeric cell-surface adhesion receptors that mediate interactions between cells and the extracellular matrix (ECM) and, in some cases, between cells and other cells. They are composed of two non-covalently associated transmembrane subunits: The α and β subunits combine to form a functional integrin receptor. Integrins are the major molecular bridges connecting the extracellular matrix to the intracellular cytoskeleton and signaling machinery. 2. Basic Structure A typical integrin spans the plasma membrane. 3. Integrin Heterodimers The functional receptor is an αβ heterodimer. Different combinations of α and β subunits produce integrins with different ligandRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Gap junctions are specialized intercellular communication channels that directly connect the cytoplasm of adjacent cells. They permit the passage of: between neighboring cells. Unlike desmosomes and adherens junctions, their primary function is not mechanical adhesion but direct intercellular communication. Core concept Gap junctions allow adjacent cells to communicate directly without releasing signals into the extracellular space. 2. Basic Structure A gap junction channel is formed by the interaction of two connexons, one contributed by each adjacent cell. The complete intercellular channel is: Connexon A + Connexon B → Gap-junction channel 3. Connexins The individual proteinsRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Hemidesmosomes are specialized cell–extracellular matrix (ECM) adhesion complexes located primarily on the basal surface of epithelial cells. They anchor the cell’s intermediate filament cytoskeleton to the basement membrane, thereby providing strong mechanical attachment between the epithelium and underlying extracellular matrix. The basic organization is: Core concept Hemidesmosomes anchor epithelial cells to the basement membrane through integrins and intermediate filaments. 2. Why Are They Called “Hemidesmosomes”? The name literally means “half desmosome.” They were originally thought to resemble half of a desmosome morphologically. However, molecularly they are quite different. Desmosome Cell → Cell Hemidesmosome Cell →Read More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Desmosomes are specialized cell–cell adhesion junctions that provide strong mechanical attachment between neighboring cells by linking desmosomal cadherins in the plasma membrane to the intermediate filament cytoskeleton. They are especially abundant in tissues exposed to mechanical stress, such as: The fundamental arrangement is: Core concept Desmosomes mechanically couple the intermediate-filament networks of neighboring cells. 2. Major Function The principal function of desmosomes is to provide high mechanical strength to tissues. They prevent cells from separating when tissues experience: 3. Location Desmosomes occur along the lateral surfaces of cells. They are particularly prominent in: Skin TheRead More →

Master’s-Level Cell Biology & Advanced Molecular Biology Notes 1. Definition Adherens junctions (AJs) are specialized cell–cell adhesion complexes that mechanically connect neighboring cells through cadherin proteins linked intracellularly to the actin cytoskeleton. They are particularly important in: The basic molecular arrangement is: 2. Core Principle The fundamental structural pathway is: Thus: Adherens junctions convert cell–cell adhesion into mechanical coupling between the actin cytoskeletons of neighboring cells. 3. Location In many epithelial tissues, adherens junctions are located below the tight-junction region. A simplified epithelial junctional arrangement is: The exact organization differs among tissues. 4. Major Functions Function Role Cell adhesion Holds neighboring cells together Mechanical couplingRead More →