Carbohydrates

Carbohydrates are the most abundant organic molecules in nature. Carbohydrates formula : (CH 2 O) n Functions of carbohydrates: Energy in the diet Storage form of energy in the body Cell membrane components Structural component of many organisms

Classification of carbohydrates Monosaccharides : simple sugars Disaccharides : contain two monosaccharides Polysaccharides : contain many monosaccharides Origin: Carbohydrates are formed in plants by a process called photosynthesis Compounds that have same chemical formula but have different structures are called isomers

Monosaccharides (Simple sugars) Aldoses Ketoses depending on they contain an aldehyde or a ketone group Hexoses (six-carbon monosaccharides): are the most common monosaccharides Glucose Fructose Galactose

Glucose : - Is an aldohexose - Is commonly Known as dextrose - Is the most important of all monosaccharides and is normally found in the bloodstream and in the tissue fluids Galactose: - Is an aldohexose - Is one of the constituents of lactose Fructose : - Is a ketohexose - Is commonly known as fruit sugar - Is one of the constituents of sucrose

Monosaccharides and its chemical reactions The hexoses either aldehydes or ketones can act as reducing agents Hexose + alkaline Cu complex (Fehling s solution or Benedict s solution) → A red-orange precipitate of Cu 2 O is formed This reaction is the basis for the test for sugar in the urine Hexoses will ferment in the presence of enzymes found in yeast

Disaccharides Sucrose :(table sugar) Glucose + Fructose Maltose :(obtained by the partial hydrolysis of starch) Glucose + Glucose Lactose :(sugar in milk) Glucose + Galactose

Disaccharides and its chemical reactions Of the three disaccharides only maltose and lactose show reducing properties with alkaline Cu complex ions. Sucrose is not a reducing sugar. Sucrose and maltose will ferment with yeast due to the presence of the enzymes sucrase and maltase. Lactose will not ferment with yeast because of the absence of the enzyme lactase

Polysaccharides - Polysaccharides are polymers of monosaccharides - Hydrolysis of Polysaccharides → monosaccharides - Three common polysaccharides: Starch Cellulose Glycogen - Plants store their food as starch -Plants use cellulose as supporting and structural parts -Animals use glycogen as a reserve supply of carbohydrate.

Properties of polysaccharides Polysaccharides have a high molecular mass Insoluble in water Tasteless Give negative tests for reducing sugars These properties are the opposite of those for monosaccharides and disaccharides

A carbohydrate that can be given intravenously is a.Cellulose b. Sucrose c.Lactose d. Glucose An example of a disaccharide is a. Glucose b. Maltose Cellulose d. Starch An example of hexose is a. Sucrose b. lactose Galactose d. Ribose

Animals store carbohydrates in the form of a.Cellulose b. Glucose b.Starch d. Glycogen An example of a polysaccharide is a.Starch b. Glycogen b.Cellulose d. All of these When sucrose is hydrolyzed, it yields a.Glucose only b.Glucose and fructose c.Glucose and galactose d.Ribose and galactose

Alkaline Cu complex ions are used to test for the presence of a.Aldehydes b. Ketones b.Acids d. Oxidizing sugars An example of a pentose is a.Maltose b. talose b.Glyceraldehyde d. Ribose