Cell Adhesion and Extracellular Matrix

A set of flashcards covering key terms and concepts related to cell adhesion and the extracellular matrix.

Secretion of ECM

The process of producing extracellular matrix components such as proteins and sugars.

Multicellularity

The state of being composed of many cells, driven by adaptations to environmental and biological threats.

Key features of multicellularity

1. Formation of a cell group 2. Cooperation among cells 3. Conflict mediation 4. Increase in group size 5. Cell specialization 6. Spatial organization of specialized cells.

Extracellular Matrix (ECM)

Composed of proteins, sugars, minerals, and fluids; provides strength, flexibility, and selective filtration between cells.

Basal Lamina

A thin sheet of ECM at the basal surface of epithelial tissues and neuromuscular junctions.

Structural glycoproteins

Proteins that have carbohydrates attached and provide structural support in the ECM.

Proteoglycans

Glycoproteins that have long chains of sugars attached, playing a role in the structure and function of the ECM.

Collagen

The most abundant protein in animals, providing structural support to tissues.

Function of collagen

To provide structural support to tissues, such as bones, skin, and connective tissues.

Structure of collagen

A triple-stranded helical structure (coiled coil) made of three protein subunits.

Types of collagen

At least 29 types, with Type I accounting for 90% of body collagen.

Classes of collagen

Four main classes include fibrillar, network-forming, fibril-associated, and transmembrane collagens.

Collagen synthesis

Synthesized as procollagen, secreted by fibroblasts, and cleaved by enzymes to allow assembly.

Ehlers-Danlos syndrome

A genetic defect in collagen resulting in hyperelastic skin and joint hypermobility.

Fibronectin

A glycoprotein that connects cells to collagen matrices and organizes the cytoskeleton.

Integrins

Receptor proteins that facilitate interaction between cells and ECM.

Extracellular domain of integrins

The part that binds ECM, allowing communication with the cytoskeleton through the intracellular domain.

Laminin

An adhesive substrate for cells that provides structural support in the ECM.

Structure of laminin

A triple-helical heterotrimer with a cross-like structure for protein binding.

Function of laminin

Forms web-like networks, such as in the basal lamina.

Basement membrane

Composed of basal lamina and reticular lamina; it supports epithelial and surrounding tissues.

Role of proteoglycans in ECM

They create a hydrated gel that resists compressive forces in joints.

Types of proteoglycans

Includes decorin, aggrecan, syndecan, and glypican; differ in attachment methods.

Glycosaminoglycans (GAGs)

Negatively charged long disaccharides that bind cations and water, influencing ECM properties.

Hyaluronic acid

Does not form proteoglycans; binds water and lubricates structures such as joints.

Function of aggrecan and hyaluronic acid

Associated with cartilage, functioning in cushioning and lubrication.

Integrin structure

Heterodimers of α and β subunits that span the membrane, linking ECM to cytoskeleton.

Adhesion proteins

Proteins that bind together on adjacent cells, crucial for multicellularity.

Receptors in cell adhesion

Proteins enabling cells to adhere to each other or the ECM, forming junctions.

Types of cell junctions

Tight junctions, adherens junctions, and desmosomes that protect and segregate cells.

Tight junctions

Small lateral contacts that form selectively permeable barriers.

Transmembrane proteins involved in tight junctions

Claudins, occludins, and Junctional Adhesion Molecules (JAM).

Structural connections of occludins

Link to connexins, connecting tight junctions to gap junctions.

Paracellular transport

Movement of substances between adjacent cells through junctions.

'Molecular sieve' in tight junctions

Filtering of molecules based on size and charge across junctions.

Permeability of tight junctions

Determined by charge-selective pores controlling ion and solute flow.

Apical vs. basal domain

The apical domain faces the cavity while the basal domain contacts the ECM.

Lateral surface of cells

The sides between apical and basal domains where junctions form.

Basolateral domain

Includes basal and lateral surfaces that face ECM and adjacent cells.

Zonula adherens

The most well-known type of adherens junction that links cells.

Function of adherens junctions

Link cells together and support tissue structure, using cadherins connected to actin.

Features of cadherins in adherens junctions

Contain cadherins that form strong adhesions to resist shear stress.

Binding characteristics of cadherins

Bind to identical cadherins on adjacent cells and intracellularly to actin.

Appearance of desmosomes

Dark bands with rod-like projections; multiple present per junction.

Desmosome definition

Spot-weld connections between cells linked by fibrils and dense plaques.

Structure of desmosomes

Suspension bridge-like structures across membranes for strong adhesion.

Inner and outer dense plaques

Components that connect to intermediate filaments within cells.

Abundance of desmosomes

Common in skin and heart muscle, where mechanical stress is prevalent.

Hemidesmosomes

Junctions at the basal surface that link cells to the ECM.

Anchorage in hemidesmosomes

Mediated by integrins, especially α6β4.

Binding properties of extracellular integrins

Bind laminin; intracellular tails connect to keratin through linker proteins.

Dynamic nature of hemidesmosomes

Allow detachment and reattachment for processes such as wound healing.

Gap junction function

Direct communication channels for small molecules between cells.

Components of gap junctions

Made of connexons (hemichannels), each formed by six connexins.

Molecule exchange in gap junctions

Enables rapid ion and molecule exchange among cells for coordination.

Cadherins role in cell adhesion

Transmembrane receptor proteins essential for cell-cell adhesion.

Activities involving cadherins

Involved in adhesion, migration, and signal transduction.

Calcium binding in cadherins

Necessary for proper folding and function.

Types of cadherins

E-, P-, N-, R-, and VE-cadherins found in adherens junctions.

Structure of cadherins

Single-span transmembrane proteins with five extracellular domains and a cytoplasmic tail.

Homophilic vs. heterophilic binding

Homophilic is same cadherins binding; heterophilic is different cadherins binding.

Role of β-catenin

Binds to cadherin tails; α-catenin links β-catenin to actin.

Signal transduction in cadherins

Involves transmission of signals, with β-catenin participating when not bound.

Cadherins in organ formation

Drive shape changes, pivotal during processes such as neural tube formation.

Selectins

Expressed only on circulatory system cells for cell adhesion.

Cytokines effect on selectins

Activate endothelial selectin expression during inflammatory responses.

Function of selectins in the immune system

Help immune cells adhere to and exit blood vessels.

Rolling stop in leukocytes

Gradual slowing down of leukocytes in vessels mediated by selectins.

Purpose of rolling stop

Ensures leukocytes stop at inflamed sites before exiting blood vessels.

Selectin ligands

Proteins with specific sugars that bind to activated selectins on inflamed endothelium.

Sialyl Lewis(x) (sLeX)

The sugar on selectin ligands that binds to selectins on activated blood vessels.