BIOC2600 1.1

• Carbohydrates are the most abundant biomolecule with functions including oxidation of carbohydrate as the central energy-yielding pathway, insoluble carbohydrate polymers serving structural and protective elements in cell walls of bacteria and plants and connective tissues in animals, other carbohydrate polymers lubricating skeletal joints, and some carbohydrate polymers covalently attaching to proteins and lipids as signals to determine the location and fate of these molecules.
• Gangliosides are membrane lipids of eukaryotic cells with a polar head group at the outer surface of the membrane that is a complex oligosaccharide.
• Lipopolysaccharides are prime targets of antibodies produced by the immune system in response to a bacterial infection.
• Lipopolysaccharides are large molecules consisting of a polysaccharide chain of O-specific chain and core linked to the lipid via covalent bond.
• Lipopolysaccharides are the dominant feature of the outer membrane of gram-negative bacteria.
• Some of the oligosaccharide moieties in gangliosides are important for the determination of blood groups in humans.
• The different classes of carbohydrates include monosaccharides, which are simple sugars with a single unit, oligosaccharides which are short chains of monosaccharide units, usually 2 - 10, and polysaccharides which have more than 20 monosaccharide units.
• Monosaccharides are the simplest subunit of carbohydrate, are water soluble, have a molecular formula of (CH2O)n, n ≥3, and most of them have a sweet taste.
• Monosaccharides can be divided into two families: aldoses which have a carbonyl group at the end of the carbon chain, and ketoses which have a carbonyl group at any other position.
• All monosaccharides with five or more carbon atoms in the backbone occur as cyclic structures.
• The carbonyl group forms a covalent bond with the oxygen of a hydroxyl group along the chain.
• Disaccharides have 2 monosaccharides joined covalently by a glycosidic bond.
• Most carbohydrates found in nature are polysaccharides, which can be homosaccharides that contain only one type of monomer, or heterosaccharides that contain two or more different types of monomers.
• Homopolysaccharides are stored forms of fuel, with the most important storage polysaccharides being starch in plant cells, glycogen in animal cells, and occur intracellularly as large clusters or granules.
• Heparin inhibits the coagulation of blood by binding to the protease inhibitor anti-thrombin (AT).
• Glycoproteins are carbohydrate-protein conjugates where glycans (polysaccharide chains) attached are branched, smaller, and more structurally diverse than the glycosaminoglycans of proteoglycans.
• Heparan sulphate is produced by all animal cells and has variable arrangements of sulphated and non-sulphated sugars.
• The point of attachment in proteoglycans is a serine residue of the sequence - Ser-Gly-X-Gly (X means any residue) of the protein via a tetrasaccharide bridge.
• Glycoconjugates are polysaccharides covalently linked to a protein or lipid and provide communication between cells and external surroundings.
• Heparin is the intracellular form of heparan sulphate and is used as an anti-coagulant.
• Mammalian cells produce at least 40 types of proteoglycans which act as tissue organisers, influence cellular activities such as growth factor activation and adhesion, and many are secreted into the extracellular matrix.
• Proteoglycans are divided into two major families: Syndecans, which have a protein with a single transmembrane domain and extracellular domain with 3-5 chains of heparan sulphate or chondroitin sulphate, and Glypicans, which are attached to the cell membrane via a lipid anchor.
• Glycolipids are polysaccharide chains covalently linked to lipids via a glycosidic bond.
• The heparin-bound AT then inactivates thrombin, factor Xa and other proteases.
• Proteoglycans have a basic proteoglycan unit consisting of a core protein covalently attached to glycosaminoglycans.
• Types of glycoconjugates include proteoglycans, glycoproteins, glycolipids, and lipopolysaccharides.
• The carbohydrate in glycoproteins is attached at its anomeric carbon through a Glycosidic link to the –OH group of Ser or Thr residue (O-linked) or N-glycosyl link to the amide nitrogen of an Asn residue (N-linked).
• Starch contains two types of glucose polymers: amylose, which are long unbranched chains of glucose residues.
• Glycogen is abundant in the liver (10% of liver mass) and also found in skeletal muscles (1-2% of muscle mass).
• Chitin is a linear homopolysaccharide composed of N-acetylglucosamine residues, with the hydroxyl group at C-2 in glucose replaced with an acetylated amino group, and is the principal component of the hard exoskeleton of arthropods.
• Some glycosaminoglycans have one or more of the hydroxyls esterified with sulfate.
• Glycogen is the main storage polysaccharide of animal cells and is highly branched, more extensively branched and more compact than amylopectin, with branch points having α1-6 linkers.
• Glycosaminoglycans are attached to extracellular proteins to form proteoglycans.
• Chondroitin sulphate and Dermatan sulphate are glycosaminoglycans that contribute to the tensile strength of cartilages, tendons, ligaments and the walls of the aorta and contribute to the pliability of skin respectively.
• Cellulose is a fibrous tough water-insoluble homopolysaccharide found in the cell walls of plants and cannot be digested by animals, serving as a source of dietary fibre.
• Amylopectin is a highly branched glucose residue.
• Keratan sulphate is a glycosaminoglycan that does not contain uronic acid and has variable sulphate content, found in cornea, cartilage, bone, and is structural from dead cells such as horns, hair, hoofs, nails, and claws.
• Glycosaminoglycans are components of the extracellular matrix, providing a porous pathway for diffusion of nutrients and oxygen to cells.
• Glycosaminoglycans are linear polymers of repeating disaccharide units, with one of the monosaccharides being either N-acetylglucosamine or N-acetylgalactosamine, and the other being a uronic acid, D-glucuronic acid, or L-iduronic acid.
• Hyaluronic acid is a glycosaminoglycan with alternating residues of D-glucouronic acid and N-acetylglucosamine with up to 50,000 repeats, serving as a lubricant in the synovial fluid of joints, giving the vitreous humor of the eye its jelly-like consistency, and is an essential component of the extracellular matrix of cartilage and tendons.