MONOSACCHARIDES  Monosaccharides are carbohydrates that cannot be hydrolyzed to obtain smaller molecules of carbohydrate.  White crystalline solids,  very soluble in water,  have sweet taste.

# CarbonsCategory NameRelevant examples 3Triose Glyceraldehyde, Dihydroxyacetone 4TetroseErythrose 5Pentose Ribose, Ribulose, Xylulose 6Hexose Glucose, Galactose, Mannose, Fructose 7HeptoseSedoheptulose 9Nonose Neuraminic acid, also called sialic acid

Hexoses hexose.  Three common sugars share the same molecular formula: C 6 H 12 O 6. Because of their six carbon atoms, each is a hexose. They are:  glucose blood sugar  glucose, "blood sugar", the immediate source of energy for cellular respiration  galactose  galactose, a sugar in milk (and yogurt), and  fructose, a sugar found in honey.

D-Glucose (Grape Sugar)  Glucose is by far the most common carbohydrate and classified as a monosaccharide,  an aldose,  a hexose  a hexose,  and is a reducing sugar. dextrose  It is known as dextrose, because it is dextrorotatory dextrorotatory

 For sugars with more than one chiral center, D or L refers to the asymmetric C farthest from the aldehyde or keto group.

Occurrence  Widely distributed in nature  Occurs in combination with other sugars forming disaccharides  Sucrose  Maltose  Lactose  Commercially obtained from starch

blood sugar  Glucose is also called blood sugar mg/dL  circulates in the blood at a concentration of mg/dL of blood in the fasting condition  Normally trace amounts pass out in urine  Increased amounts in diabetes mellitus.  74% as sweet as sucrose

Chemistry pyranose and furanose Glucose can occur both in pyranose and furanose forms Pyranose Pyranose form is more predominant due to stable ring

 D-glucose: the chair conformer Four of the five bulky groups (OH and CH 2 OH on C 2,3,4,5) on the ring are in the more stable equitorial positions!

D-fructose Fruit sugarLevulose

Fructose  Fructose is classified as a:  monosaccharide,  the most important ketose sugar,  a hexose,  and is a reducing sugar.  Fructose, along with glucose are the monosaccharides found in disaccharide, sucrose.

Sweetest of all sugars.  73% as sweet as sucrose  Fermented by yeast  Pyranose form levorotatory  Furanose form dextrorotatory

Occurrence  Occurs in plant kingdom as such  OR  OR  in combination with glucose forming  Sucrose  Animal tissues also contain it in small amounts

 Hydrolysis of cane sugar and of inulin.  Can be changed to glucose in the liver and so used in the body.  Main source of energy for the spermatozoa  Levorotatorydextrorotatory  Levorotatory (in sucrose dextrorotatory)  Shows mutarotation

Mutarotation  Unlike the other stereoisomeric forms, α and β anomers spontaneously interconvert in solution.  This is called mutarotation.

Galactose  Galactose is classified as a:  monosaccharide, aldose  an aldose, hexose  a hexose, reducing sugar  and is a reducing sugar. Dextrorotatory shows mutarotation

Occurrence  Galactose is more commonly found in the disaccharide, lactose or milk sugar. seed coat of legumes  It is found in seed coat of legumes.  32% as sweet as sucrose  C-4 epimer  C-4 epimer of glucose galactolipids  Galactose is part of nervous tissues as galactolipids

D-mannose tuberculoprotein  Present in the polysacchride component of tuberculoprotein  If ingested, it is absorbed and converted to glucose in the body  C-2 epimer  C-2 epimer of glucose Ozasone test  Cannot be differentiated from glucose by Ozasone test

Pentoses  Occur widely in animal and plant kingdom as component of polysacchride  Arabinose and xylose- glycoproteins  Ribose - RNA, ATP, GTP, NAD +, Coenzymes  Deoxyribose - DNA

Properties  May be aldoses or ketoses phenylhadrazine  Form ozasone crystals with phenylhadrazine furfural  with acids converted to furfural,  are strong reducing sugars  Not fermented by yeast

Deoxy sugars  Ribose and its related compound, deoxyribose, are the building blocks of the backbone chains in nucleic acids, better known as DNA and RNA.  Ribose is used in RNA and deoxyribose is used in DNA.

 The presence or absence of the -OH group on carbon (#2) is an important distinction between ribose and deoxyribose.  Ribose has an alcohol at carbon # 2, while deoxyribose does not have the alcohol group.  Deoxyribose give most of sugar reaction but do not form ozasones

Disaccharides  Three common disaccharides:  Sucrose — common table sugar = glucose + fructose  Lactose — major sugar in milk = glucose + galactose  Maltose — product of starch digestion = glucose + glucose

 The resulting linkage between the sugars is called a glycosidic bond. The molecular formula of each of these disaccharides isC 12 H 22 O 11 = 2 C 6 H 12 O 6 − H 2 O

Sucrose  Sucrose is made from glucose and fructose units  Sucrose or table sugar  Cane, beet sugar, Pineapple  Has no free anomeric carbon  Is a non-reducing sugar  No osazone crystals

 Dextrorotatory  on hydrolysis becomes levorotary  Invert sugar  Invert sugar 30% more sweet than sucrose  Honey is rich with invert sugar  In sucrase deficiency, malabsorption leads to diarrhea and flatulence

Maltose  Glucose+ Glucose slivary amylase on starch  Formed in vivo by action of slivary amylase on starch acidic hydrolysis of starch  In vitro formation by acidic hydrolysis of starch.  Reducing sugar  Has free anomeric carbon  forms osazone crystals  Shows mutarotation  32% as sweet as sucrose  Baby and invalid foods

Lactose  Glucose + Galactose  Milk sugar  Reducing sugar  In lactase deficiency, malabsorption leads to diarrhea and flatulence  Certain bacteria can ferment lactose to lactic acid - souring of milk. ( lactobacillus bulgaricus)  16% as sweet as sucrose (least sweet sugar)