CARBOHYDRATES Foundation Module-Phase 1 Department of Biochemistry Faculty of Medical Sciences

What are carbohydrates? Aldehyde or ketone derivatives of polyhydric alcohol Formula (CH2O)n (n > 3) Not all carbohydrates have this empirical formula: deoxysugars, aminosugars used as an energy source and in making cell structures. Energy

Sources of carbohydrate Biscuit Rice Bread Potato Wheat Oats

Do you know…. Q1: List the main functions of carbohydrates? Q2: How are carbohydrates classified? Answer Answer

Types of Carbohydrates Based on the number of monomers. Monosaccharides: 1 Disaccharides: 2 Oligosaccharides: 3-20 Polysaccharides: more than 20 Back

Q3: How to classify monosaccharides? According to the number of carbons According to functional groups Aldosugars Ketosugars

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Monosaccharide Structure (Single Sugar Unit)

Common Monosaccharides fructose (fruit sugar) galactose For your interest only How to measure Glucose

Properties of monosaccharides? A. Physical properties * Highly soluble in water * Most taste sweet   B. Chemical properties * Formation of cyclic hemiacetals or hemiketals            * New chiral center => 2 “anomers” designated a and b

groups C

3 1 2 4 5 6 Answers

Chiral centers v Penultimate OH group

Structural representation of sugars Haworth projection Fisher projection (straight chain representation) (simple ring in perspective)

Haworth projection Fisher projection

Disaccharides Sugars composed of two monosaccharides linked together by glycosidic bonds. e.g.Maltose

Common Disaccharides sucrose (table sugar) Commercially obtained from sugar cane or sugar beet

maltose (seed sugar) Used : as a nutrient (malt extract) (1,4) linkage Found in germinating grains Used : as a nutrient (malt extract) as a sweetener as a fermentative reagent

Refer: What is lactose intolerance? lactose (milk sugar) Refer: What is lactose intolerance?

Polysaccharides or glycans Complex carbohydrates that are made up of hundreds of monosaccharides linked by glycosidic bonds. Homoglycans Heteroglycans Starch Cellulose Glycogen Inulin Gums Mucopolysaccharides

Polysaccharides (Many sugar units)

Starch Test for starch? Answer

Identification of starch-Iodine test Suspensions of amylose in water adopt a helical conformation. Iodine (I2) can insert in the middle of the amylose helix to give a blue color that is characteristic and diagnostic for starch. Back to question

Cellulose

Y X Control Test Following is the test results for 3 different sugars Name the test What is in X & Z? What is in Y ? Answer

Barfoed’s test X Y Answer Following is the Barfoed’s test results for sugars. X Y Tube Y contains ……….. Maltose Glucose Lactose Answer

Seliwanoff’s test X Y Answer Following is the Seliwanoff’s test results for sugars. X Y Tube Y contains………. Glucose Maltose Fructose Answer

THE END Back to the beginning

Q1- List the main function of carbohydrates Sources of energy Form structural components cellulose, lignin, murein Molecular recognition Blood group antigens Associated with other entities DNA, RNA, glycosides, vitamins Back to the question

Q3:How to classify carbohydrates? Number of monomers Monosaccharides(1) Disaccharides(2) Oligosacchrides(2-10) Polysaccharides or glycans(>10) Homopolysaccharides Heteropolysaccharides Complex carbohydrates

Glucose measurement methods Most are enzymatic methods 3 enzyme systems are currently used : Glucose oxidase Glucose dehydrogenase Hexokinase

Glucose oxidase methods: colorimetric method

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Can have two sets of answers Benedict’s test Reducing sugar Non reducing sugar Barfoed’s test Disaccharides Monosaccharides Back

(Barfoed’s test is positive for Monosaccharides only) Glucose (Barfoed’s test is positive for Monosaccharides only) Back to the question

(Seliwanof’s test is positive for Keto sugars) Fructose (Seliwanof’s test is positive for Keto sugars) Back to the question

3 2 1 1 N0 2 Yes 3 N0 4 N0 5 Yes 4 5 Back