Regarding proteoglycans, false is
Correct Answer: They hold less amount of water
Description: When the carbohydrate chains are attached to a polypeptide chain it is called a proteoglycan. If the carbohydrate content is less than 10%, it is generally named as a glycoprotein. If the carbohydrate content is more than 10% it is a mucoprotein. (But some authors use these words as synonyms). ii. They are seen in almost all tissues and cell membranes. About 5% of the weight of the cell membrane is carbohydrates; the carbohydrate groups cover the entire surface of the cell membrane, they are called glycocalyx. Functions include their role as enzymes, hormones, transpo proteins, structural proteins and receptors. iii. Glycophorin is the major membrane glycoprotein of erythrocytes. It is a transmembrane (spans the whole thickness of the membrane) protein. Carbohydrate chains are attached to the amino-terminal poion, outside the cell surface. iv. The oligosaccharide chains of glycoproteins are composed of varying numbers of the following carbohydrate residues: Glucose (Glu); mannose (Man); galactose (Gal); Nacetyl glucosamine (GluNAc); N-acetyl galactosamine (GalNAc); arabinose (Ara); Xylose (Xyl); L-fucose (Fuc) (Fig. 6.17) and N-acetyl neuraminic acid (NANA MUCOPOLYSACCHARIDES Mucopolysaccharides or glycosamino glycans (GAG) are heteropolysaccharides, containing uronic acid and amino sugars. Acetylated amino groups, sulfate, and carboxyl groups are also generally present. Because of the presence of these charged groups, they attract water molecules and so they produce viscous solutions. Mucopolysaccharides in combination with proteins form mucoproteins. Examples of mucopolysaccharides are hyaluronic acid, heparin, chondroitin sulfate, dermatan sulfate and keratan sulfate. 1. Hyaluronic Acid It is present in connective tissues, tendons, synol fluid and vitreous humor. It serves as a lubricant in joint cavities. It is composed of repeating units of N-Acetyl-glucosamine - beta-1, 4-Glucuronic acid - beta-1-3-N-Acetyl glucosamine and so on. 2. Heparin i. It is an anticoagulant widely used when taking blood in vitro for clinical studies. It is also used in vivo in suspected thrombo-embolic conditions to prevent intravascular coagulation. It activates antithrombin III, which in turn inactivates thrombin, factor X, and factor IX. ii. Heparin is present in liver, lungs, spleen, and monocytes. Commercial preparation of heparin is from animal lung tissues. iii. It contains repeating units of sulphated glucosamine - alpha-1, 4-L-iduronic acid - and so on. (Fig. 6.24). Idose is the 5th epimer of glucose. Iduronic acid is the oxidized form of idose. Sulphated heparin or heparan sulfate is also present in tissues. 3. Chondroitin Sulphate It is present in ground substance of connective tissues widely distributed in cailage, bone, tendons, cornea, and skin. It is composed of repeating units of glucuronic acid - beta-1,3-N-acetyl galactosamine sulphate - beta-1, 4 and so on (Fig. 6.25) 4. Keratan Sulphate It is the only GAG which does not contain any uronic acid. The repeating units are galactose and N-acetyl glucosamine in beta linkage. It is found in cornea and tendons. 5. Dermatan Sulphate: It contains L-iduronic acid and N-acetyl galactosamine in beta -1, 3 linkages. It is found in skin, blood vessels, and hea valves.Ref: DM Vasudevan - Textbook of Biochemistry, 6th edition, page no: 71&72
Category:
Biochemistry
Get More
Subject Mock Tests
Practice with over 200,000 questions from various medical subjects and improve your knowledge.
Attempt a mock test nowMock Exam
Take an exam with 100 random questions selected from all subjects to test your knowledge.
Coming SoonGet More
Subject Mock Tests
Try practicing mock tests with over 200,000 questions from various medical subjects.
Attempt a mock test now