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Glycocalyx and its Functions

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The glycocalyx is a 10 to 100 nanometer thick mesh-like layer on the outer surface of the plasma membrane. It comprises membrane-associated carbohydrates or glycans such as glycoproteins, proteoglycans, and glycolipids.

The glycans trap water to form a viscous gel that acts as a molecular sieve, allowing smaller molecules to pass while restricting larger ones.

The glycocalyx plays different roles in cell-cell interactions, like cell recognition, adhesion, and signaling.

Carbohydrate receptors in the glycocalyx, such as lectins, can recognize specific glycan chains on the adjacent cell surface, allowing cell-cell adhesion.

During cell signaling, the proteoglycans and glycoproteins act as receptors for chemical messengers and activate the intracellular signaling cascade.

In humans, the glycocalyx has specific roles in certain cell types. For instance, in blood vessels, it protects the endothelial cell lining from the shear stress of the blood flow.

Overview

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The glycocalyx is a carbohydrate-rich, fuzzy-appearing layer on the outer surface of the cell membrane. It is highly hydrophilic, because of this it attracts large amounts of water to the cell's surface. This aids the cell's interaction with the watery environment and also helps it to obtain substances dissolved in the water. It is also important for cell identification, self/non-self determination, and embryonic development and is used in cell-to-cell attachments to form tissues.

Components of Glycocalyx

The glycocalyx is composed of glycoproteins, proteoglycans, glycolipids, and other soluble plasma components. A glycoprotein is a protein with carbohydrate molecules attached, which extend into the extracellular matrix as part of the glycocalyx. The attached carbohydrate molecules aid in cell recognition. Proteoglycans are generally considered the glycocalyx's backbone, consisting of a core protein with glycosaminoglycan chain linkages. There are five types of glycosaminoglycan chains: heparan sulfate, chondroitin sulfate, dermatan sulfate, keratan sulfate, and hyaluronan. The glycolipids are lipids with covalently attached sugar molecules. Soluble components of glycocalyx include various types of proteins and soluble proteoglycans. For example, albumin and orosomucoid are some soluble components derived from the bloodstream or endothelium and play a pivotal role in preserving the charge and selectivity of the barrier.

Glycocalyx and Immune System

The glycocalyx can have various roles. For example, it may have molecules that allow the cell to bind to another cell, it may contain receptors for hormones, or it might have enzymes to break down nutrients. The type of glycocalyx found in a person's body is a product of that person's genetic makeup. It gives each of the individual's trillions of cells the "identity"of belonging in the person's body. This identity is the primary way that a person's immune defense cells "know"not to attack the person's own body cells, but it also is the reason organs donated by another person might be rejected.

A section of this text is adapted from Openstax, Anatomy and Physiology 2e, Section 3.1

A section of this text is adapted from Openstax, Biology 2e, Section 5.1

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