LI Biochemistry of Cell Carbohydrates Lecture PDF

SIJ1003 BIOCHEMISTRY OF CELL LECTURE 1: CARBOHYDRATE  One of the 3 macromolecules/ macronutrient Represent the most important source of energy CARBO – HYDRATES (C) (H2O)  Classification of Carbohydrates 1. Monosaccharides 2. Disaccharides 3. Polysaccharides  Monos...

SIJ1003 BIOCHEMISTRY OF CELL LECTURE 1: CARBOHYDRATE  One of the 3 macromolecules/ macronutrient Represent the most important source of energy CARBO – HYDRATES (C) (H2O)  Classification of Carbohydrates 1. Monosaccharides 2. Disaccharides 3. Polysaccharides  Monosaccharides Simplest compound, monomeric sugars. Empirical formula= (CH2O)n Smallest molecules of monosaccharides are called trioses (3 carbon molecule). Trioses can be divided into glyceraldehyde and dihydroxyacetone. Glyceraldehydes = aldehyde = aldose Dihydroxyacetone = ketone = ketose  Same atomic composition. Different in the location of hydrogen and double bonds. This is also known as tautomers.  Number of Aldose Ketose carbon atoms 3 aldotriose ketotriose 4 aldotetrose ketotetrose 5 aldotpentose ketopentose 6 aldohexose ketohexose How do we illustrate a monosaccharide? Chiral centers– carbon atom attached to 4 different groups. The Fischer formula. Haworth formula (pyran, furan rings). Fischer & Haworth formula  Stereoisomers Isomers: - Compounds with identical molecular formulas. - Isomers can be categorized into constitutional isomers or stereoisomers. Stereoisomers: - Stereoisomers are isomeric molecules that have similar molecular formula and constitution but differ in spatial orientation. - Stereoisomers can be divided into enantiomers and diastereomers, epimers and anomers.  Enantiomers Molecules that are mirror images of one another.  Diastereomers Molecules where their chiral carbons are connected to the exactly the same substrates at differing configurations. Diastereomers are NOT mirror image. D-glucose D-Altrose  Epimers Epimers are two diastereomers that differ only at one chiral centre/ carbon. D-glucose D-mannose  Anomers Molecules that differ in configuration at the anomeric carbon. E.g:  and  configurations based on the position of OH group at C1.  Chapter 2 so far…… 1. Monosaccaharides: Glyceraldehyde and dihydroxyacetone. Tautomers Examples of aldose sugars Fisher and Haworth projection Stereoisomers:  Enantiomers  Diastereomers  Epimers  Anomers  Oligosaccharide-Disaccharides When an anomeric carbon of a carbohydrate reacts with an OH group in a slightly acidic conditions, a glycosidic bond is formed with the release of water. Component Disaccharide Description monosaccharides glucose 1α→2 sucrose common table sugar fructose product of starch glucose 1α→4 maltose hydrolysis glucose glucose 1α→1 trehalose found in fungi glucose galactose 1β→4 lactose main sugar in milk glucose galactose 1α→6 melibiose found in legumes glucose  Sucrose Most abundant disaccharide Major form of transport in plants  Lactose Found in milk Normally, when we eat something containing lactose, an enzyme in the small intestine called lactase breaks it down into simpler sugar forms called glucose and galactose. These simple sugars are then absorbed into the bloodstream and turned into energy.  Maltose Maltose is made up of two units of glucose, In nature, used by germinating seeds for energy. Slightly sweet, very soluble in water,  Polysaccharide-complex sugar 1. Storage: Starch and glycogen. 2. Structural Material: Cellulose, hemicellulose, pectin, chitin, dextran, inulin. 3. Connective tissue: Glycosaminoglycan – ex: hyaluronic acid, chondroitin sulphate, heparin, dermatan sulphate, keratan sulphate 4. Cell identification: Glycoprotein – proteoglycan. 5. Bacteria cell wall polysaccharides.  Polysaccharide-complex sugar 1. Storage: Starch and glycogen. 2. Structural Material: Cellulose, chitin, dextran, inulin. 3. Connective tissue: Glycosaminoglycan – e.g: hyaluronic acid, chondroitin sulphate, heparin, dermatan sulphate, keratan sulphate 4. Cell identification: Glycoprotein – proteoglycan. 5. Bacteria cell wall polysaccharides.  Glycogen & Starch There are stored in granules in cells. Starch is storage for plant and glycogen is storage for animal cells. Main units starch is called amylose and amylopectin. Amylose is a linear molecule (α 1-4) whereas amylopectin and glycogen are branched polymers (α 1-4 & α 1-6).  Cellulose Major polysaccharide in woody and fibrous plants. Single most abundant single polymer in the biosphere. Very strong structure – very difficult to digest. Can be digested slowly by cellulase enzyme. Linear polymer of D-glucose. Linkages are β(1-4) glycoside. Bonded to hemicellulose, pectin & lignin in plant cell walls. A lot of hydrogen bonding occur in the cellulose microfibrils. Each microfibril consist of 50-100 cellulose molecules. Cellulose can exist as fully extended chains, with each glucose residue flipped by 180° with respect to its neighbour. Cellulose structure  Glycosaminoglycan Polysaccharide found in the intercellular spaces between cells in tissues (extracellular) such as cartilage, tendon, skin, arterial wall etc. Structural importance in vertebrate animals. Major functions in the formation of matrix to hold together proteins components of skin and connective tissue. Made up of a long chain of repetitive disaccharide units, ex: chondroitin sulphate; Each disaccharide unit is made up of an amino sugar and a monosaccharide with a negatively charged (–ve) sulphate or carboxylate group (sugar acid). Several types – hyaluronate, heparin, chondroitin 4 sulphate, chondroitin 6 sulphate, dermatan sulphate, keratan sulphate.