Glycosaminoglycans: Overview, Questions, Preparation

Polysaccharides are carbohydrates that yield a large number of monosaccharide units on hydrolysis. These monosaccharides consist of glycosidic linkages. Hence, they are called glycans. 

Glycosaminoglycans (also called GAGs) are long, chained polysaccharides. They have multiple, repeating disaccharide units. GAGs are also called mucopolysaccharides, as they are viscous and have lubricating properties similar to various mucous secretions.

Glycosaminoglycans are generally linear units of polysaccharides. They are negatively charged and may or may not contain sulfate ions. They possess molecular weights anywhere between 10 and 100 kilodalton.

Based on their structure and linkages between two units, they can be classified into the following two types:

• Non-sulfated GAGs: GAGs that do not contain sulfate. For example, hyaluronic acid is a non-sulfated GAG.

• Sulfated GAGs: GAGs that contain sulfate. For example, chondroitin sulfate (CS), heparin sulfate (HS), and keratan sulfate (KS).

The disaccharide repeating regions present in GAGs consist of uronic acids and amino sugars.

All the glycosaminoglycans may exhibit different types of geometry and linkages between their units. The type of hexosamine or hexuronic acid unit they contain may also be dissimilar.

Some of the functions of GAGs are as follows:

• Proteoglycans are regularly monitored and regulated by glycosaminoglycans (GAGs), helping them to actively engage in the biological processes of the body.

• They help in the discovery of new drugs due to their structural diversity. This  makes them fit for biochemical and structural modelling.

• Ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) are major molecules that are GAGs. RNA and DNA serve various bodily functions and help in the transfer of genetic information.

• They occur on the surface of animal cells and help the cells interact with other extracellular molecules. 

• The complexity in their structure has made them the most information-dense biopolymer in nature. These biopolymers are transgenic and consist of old animal data that can be used as a piece of evidence for research.

• They also have various functions inside and outside of the animal cell. For example, heparin has the highest negative charge and serves as an anticoagulant.

The various applications of glycosaminoglycans are as follows:

• Various activators and inhibitors that are GAG based are used in the regulation of the fibroblast growth factor (FGF/FGFR) signalling cancer.

• Hyaluronic acid (HA) negatively influences cancer progression and is used to protect cartilages.

• GAGs also act as lubricators and space fillers between joints.

• They are also used as a wetting agent, and as a barrier to the flow in the synovium.

The chapter biomolecules in class 12 defines various biomolecules like carbohydrates, proteins, and nucleic acids. It also explains the characteristics and functions of these biomolecules.

It further classifies and states the structures of various mono, di, and polysaccharides. Glycosaminoglycan is one such polysaccharide whose structure and functions are mentioned in this chapter. 

Biomolecules hold a good weightage in class 12 exams and one or two questions on glycosaminoglycans may be asked.

Q: Where are glycosaminoglycans found in the human body?

Q: Which of the glycosaminoglycans is not linked to a protein core?

Q: In a repeating unit of glycosaminoglycan, how many sulfation positions are present?

Q: Why are GAGs negatively charged?

Q: What is the most abundant glycosaminoglycan found in nature?