What Is A Glycoprotein?
Glycoproteins are molecules that contain a portion of protein and at least one serving of carbohydrates. Glycoproteins are common in biology and perform various functions. Some examples of their respective functions are as structural components of cells, enzymes, or hormones.
Carbohydrates are a class of molecules in organic chemistry and biology. Classes contain many molecules, but they all contain only carbon, hydrogen, and oxygen atoms. Proteins, on the other hand, consist of different building blocks called amino acids. Amino acids contain nitrogen, which distinguishes them from carbohydrates.
Each glycoprotein contains protein and one or more additional carbohydrates. Different glycoproteins have different ratios of carbohydrates to protein, with carbohydrate mass taking under 1 percent to about 80 percent of the finished product.
O- and N- Linked Glycoproteins
Glycoproteins are categorized according to the place of attachment of carbohydrates with amino acids in proteins.
Glycoproteins associated with O are carbohydrates bound to oxygen atoms (O) of the hydroxyl group (-OH) of the R group of either the amino acid threonine or serine. O-linked carbohydrates can also bond with hydroxylysine or hydroxyproline. The process is called O-glycosylation. O-linked glycoproteins bind to sugar inside the Golgi complex.
N-linked glycoproteins have carbohydrates bound to nitrogen (N) from amino groups (-NH2) of the R-group of the amino acid asparagine. Cluster R is usually a side chain of asparagine amide. The bonding process is called N-glycosylation. N-linked glycoproteins obtain sugar from the endoplasmic reticulum membrane and are then transported to the Golgi complex for modification.
Although glycoproteins linked to O and N are the most common forms, other connections are also possible:
- P-glycoprotein glycosylation occurs when sugar is attached to phosphorus phosphoserine.
- C-Glycosylation is when sugar attaches to the carbon atoms of amino acids. An example is when mannose sugar bonds with carbon in Tryptophan.
- Glypiation is when Glycosylphosphatidylinositol (GPI) attaches to the carbon end of polypeptides.
What Is A Glycoprotein Function and Example?
- Glycoproteins function in the structure, reproduction, immune system, hormones, and protection of cells and organisms.
- Glycoproteins are found on the surface of the lipid bilayer cell membrane. Their hydrophilic properties allow them to function in aqueous environments, where they act in the introduction of cells and binding of other molecules.
- Glycoproteins surface cells are also important for cross-linking cells and proteins (e.g. Collagen) to increase tissue strength and stability.
- Glycoproteins in plant cells are what allow plants to stand upright against gravitational forces.
- Glycosylation proteins are not only important for intercellular communication. They also help organ systems communicate with each other. Glycoproteins are found in the brain’s gray matter, where they work in together with axons and synaptosome.
- Hormones may be glycoproteins. Examples include human chorionic gonadotropin (HCG) and erythropoietin (EPO).
- Blood clotting depends on glycoprotein prothrombin, thrombin, and fibrinogen.
- Cell markers may be glycoproteins. The MN blood group is due to two polymorphic forms of glycoprotein glycophorin A. Both forms differ only with two amino acid residues, but that is enough to cause problems for people receiving organs donated by someone with a different blood type. Major Histocompatibility Complex (MHC) and antigen H of the ABO blood group are distinguished by glycosylation proteins.
- Glycophorin A is also important because it is an attachment site for Plasmodium falciparum, a parasite of human blood.
- Glycoproteins are important for reproduction because they allow the binding of spe**rm cells to the surface of the ovum.
- Mucosa is a glycoprotein found in mucus. Molecules protect the sensitive surface of the epithelium, including the respiratory tract, urinary tract, digestion, and reproduction.
- The immune response depends on glycoproteins. Carbohydrate antibodies (which are glycoproteins) determine specific antigens that can be bound. B cells and T cells have glycoproteins that bind to antigens as well.
Thank you very much for reading What Is A Glycoprotein: Definition, O- and N- Linked Glycoproteins, and Functions and Example, hopefully useful.