Carbohydrates Biochemistry Lecture PDF

BIOCHEMISTRY LECTURE (MIDTERM) ༝ on the basis of number of carbon atoms they possess CARBOHYDRATES ༝ as aldoses or ketoses depending upon their groups Wha...

BIOCHEMISTRY LECTURE (MIDTERM) ༝ on the basis of number of carbon atoms they possess CARBOHYDRATES ༝ as aldoses or ketoses depending upon their groups What are carbohydrates? ༝ means “hydrate of carbon” ༝ Comes from the Latin word “saccharum” which means sugar ༝ derives from the formula Cn(H2O)m ○ Glucose: C6H12O6 or C6(H2O)6 ༝ are polyhydroxyaldehydes, polyhydroxyketones, or compounds that yield them after hydrolysis ༝ saccharides – simpler members of the CHO family Biomedical Importance ༝ Most abundant dietary source of energy ༝ Also serve as storage form of energy ༝ are precursors for many organic compounds (fats, amino acids) ༝ Participate in the structure of cell membrane & cellular functions ༝ Certain carbohydrate derivatives are used as drugs, like cardiac glycosides or antibiotics Three Classifications of CHO Monosaccharides Oligosaccharides Polysaccharides MONOSACCHARIDES ༝ are the simplest sugars ༝ cannot be hydrolyzed further into smaller units ༝ C6H12O6 ༝ contains a single carbon chain ༝ have 3 to 9 carbon atoms Nomenclature ༝ -ose indicates that a molecule is a carbohydrate ༝ tri-, tetr-, pent-, so and so forth indicate the number of carbon atoms in the chain Classification Structure of Monosaccharides Isomerism ༝ The compounds possessing identical molecular formula but different structures are called isomers Various types of isomerism 1. Structural isomerism ༝ Same molecular formula but differ from each other by having different structures. Example: ༝ Glucose and fructose ༝ C6H12O6  2. Stereoisomerism ༝ Same molecular formula and same structure but they differ in configuration ༝ Presence of asymmetric carbon atoms allow the formation of stereoisomerism A. D- and L- Isomerism - Enantiomers - are chiral molecules that are mirror images of one another - D- Monosaccharide - has the –OH group on its penultimate carbon to the C. Epimerism right - is the stereoisomerism if two monosaccharides differ - L- Monosaccharide from each other in their configuration around a single - has the –OH group on its penultimate carbon to the specific carbon (other than anomeric) atom. left D. Anomerism - These are isomers obtained from the change of position of hydroxyl group attached to the anomeric carbon - β means that the –OH on the anomeric carbon lies on the same side of the ring as the terminal –CH2O - α means that the –OH on the anomeric carbon lies on the side of the ring opposite from the terminal – CH2OH B. Optical Isomerism - An optically active compound is a compound that rotates the plane of polarized light. - The presence of asymmetrical carbon atom causes optical activity - When a beam of plane polarized light is passed through a solution of carbohydrates, it will rotate the light either to right or to left E. Pyranose and Furanose - Haworth Projection - pyran= a 6-membered hemiacetal ring - furan= a 5-membered hemiketal ring AMINO SUGARS ༝ a monosaccharide in which an –OH group is replaced by an –NH2 group ○ D-Glucosamine ○ D-Mannosamine ○ D-Galactosamine Reduction to produce Sugar Alcohols ༝ Carbonyl group is reduced to a hydroxyl group using hydrogen as the reducing agent (sugar alcohol) REACTION OF MONOSACCHARIDES ༝ drop –ose and change to – itol Oxidation ༝ To produce acidic sugars ○ Oxidation of the aldehyde end of glucose produces gluconate/gluconic acid or glucaric acid ༝ To produce uronic acid ○ Enzyme-catalyzed oxidation of the primary alcohol at carbon 6 of a hexose yields a uronic acid OLIGOSACCHARIDES to describe any of the carbohydrates that contain from 2 to 10 monosaccharide units DISACCHARIDES ༝ contain 2 monosaccharide units joined by a glycosidic bond  2Heteropolysaccharides ༝ are complex carbohydrates formed by combining carbohydrates with noncarbohydrates or carbohydrate derivatives ༝ Examples include pectin, chitin, and heparin. POLYSACCHARIDES - a carbohydrate containing a large number of monosaccharide units, each joined to the next by Most abundant naturally occurring polysaccharides one or more glycosidic bonds Structural component of cell walls in plants - Also called as glycan (alternate name) is fibrous, tasteless, odorless and insoluble in water - not sweet and most organic solvents - negative in Benedict’s Test is a linear polysaccharide of D-glucose units joined by beta-1,4-glycosidic bonds used for energy storage in plants Two types: complete hydrolysis yields only D-Glucose 1Homopolysaccharides ༝ contain only a single type of monosaccharides ༝ Examples are starch, amylose, amylopectin, cellulose, and glycogen  HEPARIN - widely used injectable blood thinner - usually stored within the secretory granules of mast cells and released only into the vasculature at sites of tissue injury - Highly sulfated polysaccharide with only 15-90 disaccharide residues per chain PECTIN - is a naturally occurring substance (a polysaccharide) found in berries, apples and other fruit - When heated together with sugar, it causes a thickening that is characteristic of jams and jellies. - is a major component of the middle lamella, where it helps to bind cells together, but is also found in primary cell walls CHITIN MODIFIED POLYSACCHARIDES - second most abundant - gives rigidity to the exoskeletons of crabs, lobsters, shrimp, insects, and other arthropods - found in the cell walls of fungi - is used commercially in coatings (extends the shelf life of fruits and meats - monosaccharide: N-acetyl-D-Glucosamine HYALURONIC ACID - contains alternating residues of N-acetyl-Beta-D- Glucosamine and D-Glucoronate - a major component of skin, where it is involved in tissue repair - is a major component of the synovial fluid, and was found to increase the viscosity of the fluid