Cellular adhesion is the binding of a cell to another cell or to a surface or matrix. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called In Mathematics, specifically in Topology, a surface is a Two-dimensional Manifold. In Biology, the extracellular matrix ( ECM) is the Extracellular part of animal tissue that usually provides structural support to the cells Cellular adhesion is regulated by specific cell adhesion molecules that interact with molecules on the opposing cell or surface. Cell Adhesion Molecules ( CAM s are Proteins located on the cell surface involved with the Binding with other cells or with the Extracellular Such adhesion molecules are also termed "receptors" and the molecules they recognize are termed "ligands" (and sometimes "counterreceptors"). In Biochemistry, a ligand ( latin ligare = to bind is a substance that is able to bind to and form a complex with a Biomolecule
Since cells are not often found in isolation, rather they tend to stick to other cells or non-cellular components of their environment, a fundamental question is: what makes cells sticky? Cell adhesion generally involves protein molecules at the surface of cells, so the study of cell adhesion involves cell adhesion proteins and the molecules that they bind to. The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called Proteins are large Organic compounds made of Amino acids arranged in a linear chain and joined together by Peptide bonds between the Carboxyl Cell Adhesion Molecules ( CAM s are Proteins located on the cell surface involved with the Binding with other cells or with the Extracellular
For a cell adhesion protein like the one shown in the diagram, the intracellular domain binds to protein components of the cell's cytoskeleton. cytoskeleton (also CSK is a cellular " Scaffolding " or " Skeleton " contained within the Cytoplasm. This allows for very tight adhesion. Without attachment to the cytoskeleton, a cell adhesion protein that is tightly bound to a ligand would be in danger of being hydrolyzed by extracellular hydrolytic enzymes. Hydrolysis is a Chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions which may go on to participate in further reactions In Biochemistry, a hydrolase is an Enzyme that catalyzes the Hydrolysis of a Chemical bond. This will tear away the layer unneeded for molecular distibution of arion cells. Then from out of the adhesion protein from the fragile cell membrane. Often the connection between the cell adhesion proteins and the cytoskeleton is not as direct as shown in the diagram. For example, cadherin cell adhesion proteins are typically coupled to the cytoskeleton by way of special linking proteins called "catenins". Cadherins are a class of type-1 Transmembrane proteins They play important roles in Cell adhesion, ensuring that cells within tissues are bound together Catenins are Proteins found in complexes with Cadherin Cell adhesion molecules of animal cells.
Prokaryotes have adhesion molecules usually termed "adhesins". The prokaryotes (proʊˈkærioʊts singular prokaryote /proʊˈkæriət/ are a group of Organisms that lack a Cell nucleus (= karyon or any other Adherence is often an essential step in bacterial Pathogenesis or Infection, required for Colonizing a new host. Adhesins may occur on pili (fimbriae), flagellae, or the cell surface. A flagellum ( plural flagella) is a tail-like structure that projects from the Cell body of certain Prokaryotic and Eukaryotic cells and it Adhesion of bacteria is the first step in colonization and regulates tropism (tissue- or cell-specific interactions). A tropism (from Greek tropos, to turn is a biological Phenomenon, indicating growth or turning movement of a biological Organism, usually a plant
Viruses also have adhesion molecules required for viral binding to host cells. A virus (from the Latin virus meaning Toxin or Poison) is a sub-microscopic infectious agent that is unable For example, influenza virus has a hemagglutinin on its surface that is required for recognition of the sugar sialic acid on host cell surface molecules. Hemagglutinin (HA or haemagglutinin ( British English) is an Antigenic Glycoprotein found on the surface of the Influenza Viruses Sugar is a class of edible Crystalline substances mainly Sucrose, Lactose, and Fructose. Sialic acid is a generic term for the N - or O -substituted derivatives of Neuraminic acid, a Monosaccharide with a nine- Carbon backbone HIV has an adhesion molecule termed gp120 that binds to its ligand CD4, which is expressed on lymphocytes. Human immunodeficiency virus ( HIV) is a Lentivirus (a member of the Retrovirus family that can lead to acquired immunodeficiency syndrome gp120 is a Glycoprotein exposed on the surface of the HIV envelope. CD4 ( Cluster of differentiation 4 is a Glycoprotein expressed on the surface of T helper cells, Regulatory T cells, Monocytes, A lymphocyte is a type of White blood cell in the Vertebrate Immune system.
Eukaryotic protozoans also express multiple adhesion molecules. Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular An example of a pathogenic protozoan is the malarial parasite (Plasmodium falciparum), which uses one adhesion molecule called the circumsporozoite protein to bind to liver cells, and another adhesion molecule called the merozoite surface protein to bind red blood cells. Malaria is a vector -borne Infectious disease caused by Protozoan Parasites It is widespread in tropical and subtropical regions including Red blood cells are the most common type of Blood cell and the Vertebrate body's principal means of delivering Oxygen to the body tissues via the Blood In human cells, which have many different types of adhesion molecules, the major classes are named integrins, Ig superfamily members, cadherins, and selectins. Human beings, humans or man (Origin 1590–1600 L homō man OL hemō the earthly one (see Humus Integrins are Cell surface receptors that interact with the Extracellular matrix (ECM and mediate various intracellular signals. The immunoglobulin superfamily (IgSF is a large group of cell surface and soluble proteins that are involved in the recognition binding or adhesion processes of cells Cadherins are a class of type-1 Transmembrane proteins They play important roles in Cell adhesion, ensuring that cells within tissues are bound together Selectins are a family of cell adhesion Molecules (or CAMs. All selectins are single-chain transmembrane Glycoproteins that share similar properties Each of these adhesion molecules has a different function and recognizes different ligands. Defects in cell adhesion are usually attributable to defects in expression of adhesion molecules.
There are the human genetic diseases caused by inability to express a specific adhesion molecule. Genetics (from Ancient Greek grc-Latn genetikos, “genitive” and that from grc-Latn genesis, “origin” a discipline of Biology, is An example is leukocyte adhesion deficiency-I (LAD-I), where patients do not express the β2-integrin subunit precursor. Leukocyte-adhesion deficiency (abbreviated LAD is a rare Autosomal recessive disorder characterized by Immunodeficiency resulting in recurrent Infections This integrin is required for leukocytes to adhere to the blood vessel wall during inflammation in order to fight infection. Inflammation ( Latin, inflamatio, to set on fire is the complex biological response of vascular tissues to harmful stimuli such as Pathogens The leukocytes from LAD-I patients fail to adhere and patients exhibit serious episodes of infection that can be life threatening. An infection is the detrimental Colonization of a host Organism by a foreign Species.
The differential adhesion hypothesis (sometimes called the "thermodynamic hypothesis") is a theory of cell adhesion advanced by Malcolm Steinberg in 1964 to explain the mechanism by which heterotypic cells in mixed aggregates sort out into isotypic territories. A holotype is one of several possible Biological types A type is what fixes a name to a Taxon.  The DAH postulates that tissues are viscoelastic liquids, and as such possess measurable tissue surface tensions. These surface tensions have been determined for a variety of tissues, including embryonic tissues and cell lines. The surface tensions correspond to the mutual sorting behavior: the tissue type with the higher surface tension will occupy an internal position relative to a tissue with a lower surface tension (if these tissues can interact with each other through their adhesion machinery). Quantitative differences in homo and heterotypic adhesion are supposed to be sufficient to account for the phenomenon without the need to postulate cell type specific adhesion systems: fairly generally accepted, although some tissue specific cell adhesion molecules are now known to exist. Tissue is a cellular organizational level intermediate between cells and a complete organism In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by