Glycosaminoglycans and Glycoproteins (Vocabulary Flashcards)

Vocabulary flashcards testing key terms and their definitions from the lecture notes on glycosaminoglycans, proteoglycans, mucopolysaccharidoses, and related glycoconjugates.

Glycosaminoglycans (GAGs)

Heteropolysaccharides that form long, unbranched, negatively charged chains; covalently linked to core proteins to form proteoglycans; also called mucopolysaccharides.

Heteropolysaccharides

Polysaccharides composed of more than one kind of monosaccharide; glycosaminoglycans are examples.

Mucopolysaccharides

Older term for glycosaminoglycans (GAGs).

Proteoglycans

Core proteins with covalently attached GAG chains; form hydrated gel in the extracellular matrix (ground substance) and interact with collagen, elastin, and fibronectin.

Ground substance

Gel-like extracellular matrix hydrated by GAGs, providing flexible support and a medium for molecular movement.

Hyaluronic acid

An unsulfated GAG; repeating disaccharide of D-glucuronic acid and N-acetylglucosamine; not covalently bound to proteins; lubricates joints and contributes to the vitreous humor; degraded by hyaluronidase.

Heparin

GAG with very high negative charge density; intracellular in mast cells; natural anticoagulant that acts via antithrombin III.

Heparan sulfate

GAG similar to heparin but with fewer sulfates; extracellular; found in basement membranes and on cell surfaces.

Chondroitin sulfate

Most abundant GAG; found in cartilage, tendons, and ligaments; repeating unit: glucuronic acid + N-acetylgalactosamine with sulfate at C-4 or C-6.

Dermatan sulfate

GAG with repeating unit L-iduronic acid + N-acetylgalactosamine; found in skin, blood vessels, and heart valves; antithrombotic but with minimal anticoagulant activity.

Keratan sulfate

Heterogeneous GAG with repeating unit of N-acetylglucosamine and galactose; no uronic acid; sulfation varies; forms include Keratan sulfate I (cornea) and Keratan sulfate II (loose connective tissue) and can associate with chondroitin sulfate.

Keratan sulfate I

Keratan sulfate form found in the cornea.

Keratan sulfate II

Keratan sulfate form found in loose connective tissue and in proteoglycan aggregates with chondroitin sulfate.

Mucopolysaccharidoses

Hereditary lysosomal storage diseases from deficient hydrolases that degrade GAGs; progressive accumulation of GAGs; autosomal recessive except Hunter (X-linked).

Hurler syndrome (MPS I H)

α-L-iduronidase deficiency; severe MPS I with corneal clouding, mental retardation, coarse facies; treated with transplantation or enzyme replacement therapy.

Hunter syndrome (MPS II)

Iduronate sulfatase deficiency; X-linked; variable severity; typically no corneal clouding; treated with enzyme replacement therapy.

Sanfilippo syndrome types A–D (MPS III)

Defects in removal of N-sulfated or N-acetylated glucosamine from heparan sulfate; severe nervous system symptoms; urinary heparan sulfate used in diagnosis.

Sly syndrome (MPS VII)

β-Glucuronidase deficiency; hepatosplenomegaly, skeletal deformities, short stature, corneal clouding, mental deficiency.

Hemicellulose

Group of branched polysaccharides resembling cellulose but more soluble; composed of pentoses and hexoses (e.g., xylose, arabinose, mannose, galactose) and their uronic acid derivatives.

Pectin

Polysaccharide of galacturonic acid linked α1→4, with galactose/arabinose branches and partial methylation; found in citrus fruits; used as a gelling agent.

Glycoproteins

Proteins with one or more covalently attached oligosaccharides; located on the plasma membrane (glycocalyx), extracellular matrix, and blood; inside cells in Golgi, secretory granules, and lysosomes; carbohydrate content 1–70% of mass; about half of mammalian proteins are glycoproteins.

N-linked oligosaccharides

Oligosaccharides attached to the amide nitrogen of asparagine (Asn) residues; tend to be complex and branched.

O-linked glycosylation

O-glycosidic bond of an oligosaccharide to serine or threonine residues in proteins.

Glycocalyx

Carbohydrate-rich layer on the exterior of the plasma membrane formed by glycoproteins and glycolipids.

N-acetylglucosamine (GlcNAc)

Amino sugar that is a building block of GAG disaccharides; often acetylated.

N-acetylgalactosamine (GalNAc)

Amino sugar that is a building block of GAG disaccharides; often sulfated.

D-Glucuronic acid

An acidic sugar (uronic acid) used in GAG repeating disaccharides.

L-iduronic acid

Another uronic acid component of GAG repeating disaccharides.

N-acetylneuraminic acid (NeuAc)

Sialic acid; terminal sugar commonly found on glycoproteins and glycolipids.

Fucose (Fuc)

Deoxyhexose sugar found in certain glycoproteins and glycan structures.

Xylose (Xyl)

Pentose sugar; component of glycoprotein glycan chains.

Arabinose (Ara)

Pentose sugar; component of some plant and fungal glycans.

Galactose (Gal)

Hexose sugar; component of many glycoprotein and glycolipid glycans.

Mannose (Man)

Hexose sugar; common in N-linked glycans and glycoprotein structures.

Sialic acids

Derivative of neuraminic acid; terminal residues on many glycoproteins; NeuAc is the predominant form.