Carbohydrates 2023/2024 PDF

2023/2024 Biochemistry ‫ال‬ CARBOHYDRATS Definition of carbohydrates:- They are biomolecules, found abundantly in living organisms. Carbohydrates...

2023/2024 Biochemistry ‫ال‬ CARBOHYDRATS Definition of carbohydrates:- They are biomolecules, found abundantly in living organisms. Carbohydrates have a wide range of functions. They provide energy; act as storage molecules of energy. Serve as cell membrane components and mediate some forms of communication between cells. Carbohydrates are the most abundant macromolecules in nature. They are the main source and storage of energy in the body. They serve also as structural component of cell membrane. The general molecular formula of carbohydrate is CnH2nOn or (CH2O)n, where n > 3. Chemically, they contain the elements Carbon, hydrogen and oxygen. Thus they are Carbon compounds that contain large quantities of Hydroxyl groups. Carbohydrates in general are polyhydroxy aldehydes or ketones or compounds which give these substances on hydrolysis. 1 2023/2024 Biochemistry ‫ال‬ There are three major classes of carbohydrates  Monosaccharaides (Greek, mono = one (.  Oligosaccharides (Greek, oligo= few) 2-10 monosaccharide units.  Polysaccharides (Greek, Poly = many) >10 monosaccharide units. Simplest group of carbohydrates and often called simple sugars since they cannot be further hydrolyzed. Colorless, crystalline solid which are soluble in water and insoluble in a non-polar solvent. These are compound which possesses a free aldehyde or ketone group. The general formula is Cn(H2O)n or CnH2nOn They are classified according to the number of carbon atoms they contain and also on the basis of the functional group present. The monosaccharaides thus with 3,4,5,6,7… carbons are called trioses, tetroses, pentoses, hexoses, heptoses, etc., and also as aldoses or ketoses depending upon whether they contain aldehyde or ketone group. Examples: Glucose, Fructose, Erythrulose, Ribulose. 2 2023/2024 Biochemistry ‫ال‬ Examples of monosaccharaides:- Glucose It is a simple sugar having a molecular formula C6H12O6. In simple terms, we can say that it is made up of six carbon atoms, twelve hydrogen atoms and six oxygen atoms. Glucose is a widely available monosaccharide and is also known as dextrose and blood sugar. Some properties of glucose The main source of energy Binds to other sugars to give disaccharides, oligo and poly saccharides It is aldo hexose, glucopyranose It is called Dextrose It is reducing sugar It is called also grape sugar 3 2023/2024 Biochemistry ‫ال‬ Monosaccharaides are named by: Prefix of the Latin number of the carbon atoms forming the sugar + the suffix -ose Arabic number Latin sugar 3 Tri- Aldo Triose Keto Triose 4 Tetra- Aldo Tetrose Keto Tetrose 5 Pent- Aldo Pentose Keto Pentose 6 Hex- Aldo Hexose Keto Hexose 7 Hept- Aldo Heptose Keto Heptose 8 Oct- Aldo Octose Keto Octose 4 2023/2024 Biochemistry ‫ال‬ Notice, you can find two forms of monosaccharaides having the same number of carbon atoms(aldose and ketoses). - The simplest monosaccharaides is trioses having carbons 3. Two trioses are present; glyceraldehyde and dihydroxyacetone. Notice, Both can be written( C3H6O3) or (CH2O)3 One is aldotriose and the other is ketotriose. monosaccharaides having 6 carbons are glucose -and fructose. Notice, Both can be written C6H12O6 or (CH2O)6 One is aldohexose and the other is ketohexose. Notice, Many other aldohexoses and ketohexoses are present. :- Oligosaccharides are compound sugars that yield 2 to 10 molecules of the same or different monosaccharaides on hydrolysis. The monosaccharide units are joined by glycosides linkage. Based on the number of monosaccharide units, it is further ,classified as disaccharide, tri saccharide, tetra saccharide etc. Oligosaccharides yielding 2 molecules of monosaccharaides on hydrolysis is known as a disaccharide, and the ones yielding 3 or 4 monosaccharaides are known as tri saccharides and tetra saccharides respectively and so on. The general formula of disaccharides is Cn(H2O)n-1 and that of tri saccharides is Cn(H2O)n-2 and so on. 5 2023/2024 Biochemistry ‫ال‬ Examples: Disaccharides include sucrose, lactose, maltose, etc. Tri saccharides are Raffinose, Rabinose. Some of structure disaccharide:- 6 2023/2024 Biochemistry ‫ال‬ 7 2023/2024 Biochemistry ‫ال‬ Polysaccharides They are also called as “glycan". Polysaccharides contain more than 10 monosaccharide units and can be hundreds of sugar units in length. They yield more than 10 molecules of monosaccharaides on hydrolysis. Polysaccharides differ from each other in the identity of their recurring monosaccharide units, in the length of their chains, in the types of bond linking units and in the degree of branching. They are primarily concerned with two important functions ie. Structural functions and the storage of energy. They are further classified depending on the type of molecules produced as a result of hydrolysis. They may be homopolysaccharidese, containing monosaccharaides of the same type or heteropolysaccharides i.e., monosaccharaides of different types. Examples of Homopolysaccharides are starch, glycogen, cellulose, pectin. Heteropolysaccharides are Hyaluronic acid, Chondroitin. 8 2023/2024 Biochemistry ‫ال‬ - Types:- There are three important polysaccharides Starch Glycogen Cellulose 9 2023/2024 Biochemistry ‫ال‬ This is the plant storage polysaccharide. It is insoluble and forms starch granules inside many plant cells. It is not a pure substance, but is a mixture of amylose and amylopectin. Amylose and amylopectin. Amylose Is simply poly-(1-4) glucose, so is a straight chain. In fact the chain is floppy, and it tends to coil up into a helix. Amylopectin Is poly(1-4) glucose with about 4 (1-6) branches. This gives it a more open molecular structure than amylose. Because it has more ends, it can be broken more quickly than amylose by amylase enzymes. Both amylose and amylopectin are broken down by the enzyme amylase into maltose, though at different rates. The enzyme can only break down the 1-4 bond not the 1-6 so starch is broken down into glucose and a disaccharide. 11 2023/2024 Biochemistry ‫ال‬ This is similar in structure to amylopectin. It is poly (1-4) glucose with 9 (1-6) branches. It is made by animals as their storage polysaccharide, and is found mainly in muscle and liver. Because it is so highly branched, it can be mobilised (broken down to glucose for energy) very quickly. It is broken down to glucose by the enzyme glycogen phosphorylase. This is only found in plants, where it is the main component of cell walls. It is poly (1-4) glucose, but with a different isomer of glucose. Starch and glycogen contain a-glucose, in which the hydroxyl group on carbon 1 sticks down from the ring, while cellulose contains ß-glucose, in which the hydroxyl group on carbon 1 sticks up. This means that in a chain alternate glucose molecules are inverted. Properties of Carbohydrates:- Physical Properties of Carbohydrates 1-Stereoisomerism: Compound shaving the same structural formula but they differ in spatial configuration. Example: Glucose has two isomers with respect to the penultimate carbon atom. They are D-glucose and L-glucose. 2-Optical Activity: It is the rotation of plane-polarized light forming (+) glucose and (-) glucose. 11 2023/2024 Biochemistry ‫ال‬ 3-Diastereo isomers: It the configurationally changes with regard to C2, C3, or C4 in glucose. Example: Mannose, galactose. 4-Annomerism: It is the spatial configuration with respect to the first carbon atom in aldoses and second carbon atom in ketoses. Chemical Properties of Carbohydrates 1-Osazone formation: Osazone are carbohydrate derivatives when sugars are reacted with an excess of phenyl hydrazine. eg. Glucosazone. 2-Benedict’s test: Reducing sugars when heated in the presence of an alkali gets converted to powerful reducing species known as enediols. When Benedict’s reagent solution and reducing sugars are heated together, the solution changes its color to orange-red/ brick red. 3-Oxidation: Monosaccharaides are reducing sugars if their carbonyl groups oxidize to give carboxylic acids. In Benedict’s test, D-glucose is oxidized to D-gluconic acid thus, glucose is considered a reducing sugar. 4-Reduction to alcohols: The C=O groups in open-chain forms of carbohydrates can be reduced to alcohols by sodium borohydride, NaBH4, or catalytic hydrogenation (H2, Ni, EtOH/H2O). The products are known as “alditols”. :- Living organisms use carbohydrates as accessible energy to fuel cellular reactions. They are the most abundant dietary source of energy (4kcal/gram) for all living beings Carbohydrates along with being the chief energy source, in many animals, are instant sources of energy. Glucose is broken down by glycolysis / Kreb’s cycle to yield ATP. 12 2023/2024 Biochemistry ‫ال‬ Serve as energy stores, fuels, and metabolic intermediates. It is stored as glycogen in animals and starch in plants. Stored carbohydrates act as an energy source instead of proteins. They form structural and protective components, like in the cell wall of plants and microorganisms. Structural elements in the cell walls of bacteria (peptidoglycan or murine ), plants (cellulose) and animals (chitin). Carbohydrates are intermediates in the biosynthesis of fats and proteins. Carbohydrates aid in the regulation of nerve tissue and is the energy source for the brain. Carbohydrates get associated with lipids and proteins to form surface antigens, receptor molecules, vitamins and antibiotics. 13