Glycocalyx
Encyclopedia
Glycocalyx is a general term referring to extracellular polymer
ic material (glycoprotein
) produced by some bacteria
, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide
matrix excreted by epithelial cells forming a coating on the surface of epithelial tissue. External to the plasma membrane, all animal cells have a fuzzy coat called the glycocalyx. This coat consists of the carbohydrate moieties of membrane glycolipids and glycoproteins. Only identical twins have chemically identical glycocalices; everyone else is unique. The glycocalyx is a type of identification that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, and invading organisms. The glycocalyx also includes the cell-adhesion molecules that enable cells to adhere to each other and guide the movement of cells during embryonic development. Studies have shown that the glycocalyx plays a role in modulating red blood cell filling in capillaries and it is also believed to be important in many other functions of the vascular system, but studies are ongoing.
s that project from cellular surfaces, e.g. those of bacteria. It serves to protect the bacterium by creating capsules, or allows the bacterium to attach itself to inert surfaces (like teeth or rocks; e.g. Streptococcus pneumoniae
attaches itself to lung cells), prokaryotes, or other bacteria (their glycocalyxes can fuse to envelop the colony).
The glycocalyx can be found just outside the cell wall of a bacterium. A distinct, gelatinous glycocalyx is called a Bacterial capsule, while an irregular, diffuse layer is called a slime layer
. Glycocalyx can help protect bacteria from phagocyte
s. It also helps in the formation of biofilm
s such as a coating on inert surfaces such as catheters, teeth or rocks.
plasma membrane of epithelial absorptive cells. It provides additional surface for adsorption
and includes enzyme
s secreted by the absorptive cells that are essential for the final steps of digestion of proteins and sugars.
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic material (glycoprotein
Glycoprotein
Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as glycosylation. In proteins that have segments extending...
) produced by some bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, epithelia and other cells. The slime on the outside of a fish is considered a glycocalyx. The term was initially applied to the polysaccharide
Polysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
matrix excreted by epithelial cells forming a coating on the surface of epithelial tissue. External to the plasma membrane, all animal cells have a fuzzy coat called the glycocalyx. This coat consists of the carbohydrate moieties of membrane glycolipids and glycoproteins. Only identical twins have chemically identical glycocalices; everyone else is unique. The glycocalyx is a type of identification that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, and invading organisms. The glycocalyx also includes the cell-adhesion molecules that enable cells to adhere to each other and guide the movement of cells during embryonic development. Studies have shown that the glycocalyx plays a role in modulating red blood cell filling in capillaries and it is also believed to be important in many other functions of the vascular system, but studies are ongoing.
Glycocalyx of bacteria
A glycocalyx, literally "sugar coat", is a network of polysaccharidePolysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
s that project from cellular surfaces, e.g. those of bacteria. It serves to protect the bacterium by creating capsules, or allows the bacterium to attach itself to inert surfaces (like teeth or rocks; e.g. Streptococcus pneumoniae
Streptococcus pneumoniae
Streptococcus pneumoniae, or pneumococcus, is Gram-positive, alpha-hemolytic, aerotolerant anaerobic member of the genus Streptococcus. A significant human pathogenic bacterium, S...
attaches itself to lung cells), prokaryotes, or other bacteria (their glycocalyxes can fuse to envelop the colony).
The glycocalyx can be found just outside the cell wall of a bacterium. A distinct, gelatinous glycocalyx is called a Bacterial capsule, while an irregular, diffuse layer is called a slime layer
Slime layer
A slime layer in bacteria is an easily removed, diffuse, unorganized layer of extracellular material that surrounds bacteria cells. Specifically, this consists mostly of exopolysaccharides, glycoproteins, and glycolipids....
. Glycocalyx can help protect bacteria from phagocyte
Phagocyte
Phagocytes are the white blood cells that protect the body by ingesting harmful foreign particles, bacteria, and dead or dying cells. Their name comes from the Greek phagein, "to eat" or "devour", and "-cyte", the suffix in biology denoting "cell", from the Greek kutos, "hollow vessel". They are...
s. It also helps in the formation of biofilm
Biofilm
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance...
s such as a coating on inert surfaces such as catheters, teeth or rocks.
Glycocalyx in the digestive tract
A glycocalyx can also be found on the apical portion of microvilli within the digestive tract, especially within the small intestine. It creates a meshwork 0.3 micrometers thick and consists of acidic mucopolysaccharides and glycoproteins that project from the apicalApical
Apical, from the Latin apex meaning to be at the apex or tip, may refer to:*Apical , an anatomical term of location for features associated with the base of an organism or structure...
plasma membrane of epithelial absorptive cells. It provides additional surface for adsorption
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
and includes enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s secreted by the absorptive cells that are essential for the final steps of digestion of proteins and sugars.
Functions
- Protection: Cushions the plasma membrane and protects it from chemical injury
- Immunity to infection: Enables the immune systemImmune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
to recognize and selectively attack foreign organismOrganismIn biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...
s - Defense against cancer: Changes in the glycocalyx of cancerCancerCancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
ous cells enable the immune systemImmune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
to recognize and destroy them - Transplant compatibility: Forms the basis for compatibility of blood transfusions, tissue grafts, and organ transplantOrgan transplantOrgan transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
s - Cell adhesion: Binds cells together so that tissues do not fall apart
- Inflammation regulation: Glycocalyx coating on endothelial walls in blood vessels prevents leukocytes from rolling/binding in healthy states
- Fertilization: Enables spermSpermThe term sperm is derived from the Greek word sperma and refers to the male reproductive cells. In the types of sexual reproduction known as anisogamy and oogamy, there is a marked difference in the size of the gametes with the smaller one being termed the "male" or sperm cell...
to recognize and bind to eggs - Embryonic development: Guides embryonic cells to their destinations in the body