Concepts of Carbohydrates PDF

(003) CONCEPTS OF CARBOHYDRATES DR. AMADO VIESTA JR.| 10/13/2020 OUTLINE I. ALDOLASE, KETOSES, FISCHER PROJECTION AND EPIMERS II. CYCLIC FORMS OF CHO A. ALDOHEXOSES B. KETOHEXOSES...

(003) CONCEPTS OF CARBOHYDRATES DR. AMADO VIESTA JR.| 10/13/2020 OUTLINE I. ALDOLASE, KETOSES, FISCHER PROJECTION AND EPIMERS II. CYCLIC FORMS OF CHO A. ALDOHEXOSES B. KETOHEXOSES III. GLYCOSIDIC/NON-REDUCING SUGARS A. BETA-1,4-GLYCOSIDIC LINKAGE -Horizontal lines are drawn in front of the plane (coming B. ALPHA-1,2-GLYCOSIDIC LINKAGE out of the board), while vertical lines are drawn in the IV. POLYSACCHARIDES back of the plane (going back into the board) Diastereomers- when 2 sugars have identical molecular I. ALDOLASE, KETOSES, FISCHER PROJECTION ⚫ formulas, have different arrangement of atoms and are AND EPIMERS not enantiomer ⚫ Monosaccharides- The simplest sugars -(C.H2O)- Empirical formula -Monosaccharides can be ALDEHYDE or ketones, the smallest functional monosaccharides n+3 ⚫ Epimers- Sugars that differ in stereochemistry only at a single chiral carbon ⚫ Ketoses- monosaccharides that have acetone group (ie. DHA) ⚫ Aldolases- monosaccharides that have aldehyde group -The symbol D and L designates the absolute configuration of stereogenic or chiral carbon that is farthest away from the aldehyde group II. CYCLIC FORMS OF CHO -Although sugar do exist as open chains, they can cyclize to ⚫ Enantiomers- sugars that MIRROR images of one another form ring structures -in D-isomers, the -OH points to the right and L-isomers -These ring structures generally predominate under normal points to the left physiological conditions because they are lower in energy and more stable than their open chain ⚫ Fischer Projection- commonly used to describe the counterparts stereochemistry of sugar -The basis of this reaction is the nucleophilic attack of the carbonyl group by an alcohol group PREPARED AND EDITED BY: PADOLINA, J.  (003) CONCEPTS OF CARBOHYDRATES DR. AMADO VIESTA JR.| 10/13/2020 ⚫ Nucleophile- provides electrons for making a new bond A. KETOHEXOSES (5 to 6 membered ring) (alcohol group) ⚫ Electrophile- accepts electrons in chemical reactions (carbon of carbonyl) ⚫ Hemiacetal formation- alcohol bingding to an aldehyde -For D-fructose (a ketohexoses), the hydroxyl group of the 5th ⚫ Hemiketal formation- alcohol binding to a ketone carbon reacts with the ketone group (2nd carbon) to produce a five-membraned ring A. ALDOHEXOSES (6-membered ring) ⚫ Fructopyranoses- a second reaction with the D-fructose. - In this reaction, the hydroxyl of the 6th carbon reacts with the ketone group to form a six-membered ring III. GLYCOSIDIC/NON-REDUCING SUGAR ⚫ Glycosidic linkage -monomeric sugars or monosaccharides are mostly found in their cyclic hemicetal form. -can transform into GLYCOSIDE -For D-glucose (an aldohexoses), the hydroxyl group on the 5th carbon reacts with the aldehyde group to formed mixture of two types of isomers the α and β anomers -α - anomers means that the OH grp in the 1st carbon points to opposite direction of the -Ch2Oh group -β - anomers means that they point in the same direction -Carbohydrates can exist as dimeric and polymeric -Whereas Fischer projection are used to describe the form. stereochemistry of open chain sugars, the Haworth projection are used to describe the stereochemistry of -Some common disaccharides: Sucrose cyclic sugars Maltose Lactose -Glycosidic Bond- connects each individual sugar molecule in long chain CHO PREPARED AND EDITED BY: PADOLINA, J.  (003) CONCEPTS OF CARBOHYDRATES DR. AMADO VIESTA JR.| 10/13/2020 A. Beta-1,4- glycosidic linkage ⚫ Lactose- combination of D-galactose and D-glucose -the glycosidic bond begins on the 1st carbon of D-galactose and ends on the 4th carbon of D- glucose. -Notice that the galactose is the β anomer. Thus the linkage is β-1,4 -is a Reducing sugar because it has free hemiacetal portion on the second sugar (glucose): -This HEMIACETAL can open up to form free aldehyde group that can be oxidized in the presence of H2O -Other examples would be other monosaccharides such as Galactose, Mannose, Ribose: -Another example would certain disaccharides such as Maltose: IV. POLYSACCHARIDES -Largest CHO that consists of many monosaccharides linked by O-glycosidic bonds -Has 2 impostant roles: B. Alpha-1,2 glycoside linkage a. Energy storage ⚫ Sucrose- combination of glucose and fructose. b. Structure and protection -However, the linkage is slightly different than in lactose ⚫ Homopolysaccharides -the linkage is between the first carbon and the - polysaccharides in which all the monosaccharides are second carbon the same -It is as Non-reducing sugar since both of the sugars are connected to the anomeric carbon ⚫ Glycogen (COOH in the cyclic group) - the most common polysaccharides in animals and -They have NO hemiacetal or with acetal humans group to transform into a free aldehyde and so - these are homopolymers that consists of glucose well not be oxidized monosaccharides - linked via α-1,4-glycosidic bonds in helical fashion. The helical chain is branched every 10 or so units via α-1,6- glycosidic bond - HIGHLY BRANCHED PREPARED AND EDITED BY: PADOLINA, J.  (003) CONCEPTS OF CARBOHYDRATES DR. AMADO VIESTA JR.| 10/13/2020 ⚫ Cellulose - Polysaccharide in plants which plays a structural role - consists of glucose monomers linked together via β-1,4- glycosidic bonds, unbranched - The β-1,4 linkaged allows cellulose to form very long, linear fibers. - Many fibers can stack on top of one another via hydrogen bonds. This makes cellulose optimal for providing structure, protection and support to plants ⚫ Starch - The most common in PLANTS polysaccharides - 2 forms: a. Amylose - unbranched that consist of glucose polysaccharides connected via α-1,4- glycosidic bonds b. Amylopectin- branched polysaccharide that consists of glucose monomers linked REFERENCES via α-1,4-linkaged and branches Dr. Viesta’s lecture connected via α-1,6-glycosidic bonds. - Branches occur ever 30 or so units ⚫ Amylase - enzyme that breaks down starch in humans PREPARED AND EDITED BY: PADOLINA, J.