Transcript Lecture 1
CARBOHYDRATES LECTURE OUTLINE By the end of the lecture, the student should know: The Importance of carbohydrates. The Definition of Carbohydrates. The Classification of Carbohydrates. The Difference between various Isomers.. CARBOHYDRATE: IMPORTANCE Most Abundant Class of Biomolecules. An Important Macronutrient. Performs important physiological functions in the body. Associated with Pathological Conditions (Diabetes Mellitus, Lactose Intolerance). DEFINING CARBOHYDRATES Carbohydrates or Saccharides (Greek Sakcharon meaning "Sugar") Organic compounds composed of Carbon, Hydrogen and oxygen. Many Carbohydrates also contain Nitrogen and other elements. Carbohydrates derive their name from a Misleading Concept 'Hydrates of Carbon’ Hydrogen and Oxygen in Carbohydrates were found to be present in the same proportion as in water. (2:1).(E.g. Glucose C6H12O6 or C6 (H2O)6). It is due to this fact that compounds derived their name “Carbon Hydrate”. GLUCOSE H-C=O H-C-OH OH-C-H H-C-OH H-C-OH CH2OH This term is not a perfect derivation as many carbohydrates do not have the same proportion as water. Example: DEOXYRIBOSE (C5H10O4) H-C=O H-C-H H-C-OH H-C-OH CH2OH CHEMICAL DEFINITION OF CARBOHYDRATES Polyhydroxyl: Having more than one hydroxyl group. (-OH) Functional Group: It is a specific group of atoms or bonds which are part of a larger hydrocarbon chain.(Provide a specific chemical behaviour). For carbohydrates, the functional group is the carbonyl group which may be either Aldehyde Group (H-C=O) Or Keto Group (C=O) WHAT IS SIMILAR & DIFFERENT IN THESE TWO STRUCTURES? H-C=O CH2OH H-C-OH C=O one hydroxylgroup in both More than OH-C-H OH-C-H H-C-OH H-C-OH CH2OH CH2OH WHAT IS COMMON & DIFFERENT IN THESE TWO STRUCTURES? H-C=O CH2OH H-C-OH C=O Carbonyl Group inboth But? OH-C-H OH-C-H H-C-OH H-C-OH CH2OH CH2OH WHAT IS COMMON & DIFFERENT IN THESE TWO STRUCTURES? H-C=O CH2OH H-C-OH C=O Aldehyde in 1 and Ketone in 2 OH-C-H OH-C-H H-C-OH H-C-OH CH2OH CH2OH Carbohydrates are Polyhydroxy Alcohols with Carbonyl groups Which May Either Be Aldehyde (H-C=O) or Keto (C=O) Groups. H-C CH2OH CAN YOU O VISUALIZE C H-C-OH EITHER ALDEHYDE OH-C-H OH-C-H OR H-C-OH KETONE H-C-OH GROUP IN H-C-OH H-C-OH THIS POLYHYDROX CH2OH CH2OH Y ALCOHOL? NO! BUT HYDROLYSIS OF THIS COMPOUND YIELDS TWO COMPOUNDS WITH ALDEHYDE OR KETONE GROUPS H-C CH2OH HOH O C H-C-OH OH-C-H OH-C-H H-C-OH H-C-OH H-C-OH H-C-OH CH2OH CH2OH NO! BUT HYDROLYSIS OF THIS COMPOUND YIELDS TWO COMPOUNDS WITH ALDEHYDE OR KETONE GROUPS H-C =O CH2OH HOH O O=C H-C-OH OH-C-H OH-C-H H-C-OH H-C-OH H-C-OH H-C-OH CH2OH CH2OH MANY POLYHYDROXY ALCOHOLS MAY NOT HAVE AN ACTIVE ALDEHYDE OR KETONE GROUP BUT THEY MAY YIELD THEM ON HYDROLYSIS. THEY ARE ALSO DESIGNATED AS CARBOHYDRATES. THEREFORE, THE COMPLETE DEFINITION OF CARBOHDRATES IS: CARBOHYDRATES ARE POLYHYDROXYL ALCOHOLS WITH POTENTIALLY ACTIVE CARBONY GROUPS WHICH MAY BE EITHER AN ALDEHYDE OR KETONE GROUP. THEY ALSO CONTAIN THOSE COMPOUNDS, WHICH YIELD THEM ON HYDROLYSIS. CLASSIFICATION OF CARBOHYDRATES Carbohydrates are mainly classified into four different groups: Monosachharides Disaccharides Oligosaccharides Polysaccharides MONOSACCHARIDES Monosaccharides are those carbohydrates which Cannot be Hydrolyzed further into more simple carbohydrates. Thus, they are the Simplest form of Carbohydrates. Familiar examples are: Glucose, Fructose, Ribose & Galactose. MONOSACCHARIDES ARE FURTHER CLASSIFIED ON THE BASIS OF: Aldehyde or Ketone Group: Aldomonosaccharides (Aldoses). Ketomonosaccharides (Ketoses). Carbon Chain Length. Trioses. Tetroses. Pentoses. Hexoses. Heptoses. CARBONYL GROUP H-C=O H-C-OH OH-C-H H-C-OH H-C-OH CH2OH GLUCOSE FRUCTOSE--> CH2OH C=O OH-C-H H-C-OH H-C-OH CH2OH CARBON CHAIN H-C=O H-C-OH OH-C-H H-C-OH H-C-OH CH2OH GLUCOSE ARABINOSE--> H-C=O OH-C-H H-C-OH H-C-OH CH2OH EXAMPLES OF MONOSACCHARIDES NO. OF CARBON ATOMS ALDO KETO 3C TRIOSE GLYCERALDEHYD E DIHYDROXYACET ONE 4C TETROSE ERYTHROSE ERYTHRULOSE 5C PENTOSE RIBOSE, XYLOSE RIBULOSE, XYLULLOSE 6C HEXOSE GLUCOSE, GALACTOSE, MANNOSE FRUCTOSE GLYCERALDEHYDE GLYCERALDEHYDE IS THE SIMPLEST MONOSACCHARIDE(PARTICULARLY ALDOSES) IT CANNOT BE HYDROLYZED FURTHER. IT IS THE SMALLEST POSSIBLE STRUCTURE THAT IS A CARBOHYDRATE CANNOT HAVE LESS THAN 3 CARBON ATOMS. GENERAL FORMULA OF MONOSACCHARIDE: (C•H2O)N (WHERE N IS ANY NUMBER OF THREE OR GREATER) ISOMERISM Isomers are basically molecules that have the same chemical formula but they differ in their chemical structures. Asymmetric Carbon is an important determinant of Isomerism. Asymmetric Carbon is that Carbon which is attached with four different groups. STRAIGHT CHAIN STRUCTURE OF TYPICAL MONOSACCHARIDE (GLUCOSE) Anomeric Carbon Epimeric Carbons Penultimate Carbon Terminal Alcohol Carbon THE ASSIGNMENT OF D OR L IS MADE ACCORDING TO THE ORIENTATION OF THE PENULTIMATE CARBON If the Hydroxyl Group is on the right the molecule is a D sugar, Otherwise It is an L sugar. OH H L-Sugar : D-Sugar D AND L ISOMERISM PRODUCE MIRROR IMAGES EPIMERISM Isomers which differ from each other only with regard to oh group on a single asymmetric carbon atom. OPTICAL ISOMERS When a beam of polarized light is passed through sugars, they will be rotated either towards right or left. Right Rotation (dextrorotatory) E.g. D- Glucose Left Rotation (levorotatory) E.g. DFructose MONOSACCHARIDE DERIVATIVES OF BIOLOGICAL IMPORTANCE Oxidation Products (Sugar Acids) Reduction Products (Sugar Alcohols). Amino Sugar Sugars. Phosphates. OXIDATION PRODUCTS (SUGAR ACIDS) When oxidized under proper conditions, Aldoses may form three types of acids (Sugar Acids): Uronic Acids. Aldonic acids. Saccharic Acids. Type of sugar Acid produced depends on which carbon is oxidized. H-C=O H-C-OH OH-C-H H-C-OH H-C-OH COOH CH2OH URONIC ACID Oxidation Of Aldose At Primary Alcohol (Terminal Carbon) COOH H-C=O H-C-OH OH-C-H H-C-OH H-C-OH CH2OH ALDONIC ACID Oxidation Of Aldose At Carbonyl Carbon (Aldehyde Group) COOH H-C=O H-C-OH OH-C-H H-C-OH H-C-OH CH2OH COOH Saccharic Acid Oxidation Of Aldose At Both Aldehyde & Terminal Carbons EXAMPLES OF ALDOSES WITH THEIR CORRESPONDING URONIC ACIDS ARE: Sugar Glucose Uronic Acids Glucuronic acid, Iduronic acid ------------- ---------------------Mannose Mannuronic acid ------------- ---------------------Galactose Galacturonic acid ------------- ------------------------ EXAMPLES OF ALDOSES WITH THEIR CORRESPONDING ALDONIC ACIDS ARE: Sugar Glucose ------------Mannose ------------Galactose ------------- Aldonic Acids Gluconic acid ---------------------Mannonic acid ---------------------Galactonic acid ------------------------ Amino Sugar: H-C=O NH2 H-C-OH OH-C-H H-C-OH H-C-OH CH2OH Substitution of Amino Group for a Hydroxyl Group of a Sugar Results in the Formation of an Amino Sugar. The Amino Group is attached to Carbon 2. COMMON EXAMPLES OF AMINO SUGARS (AMINOSACCHARIDES) Galactosamine Glucosamine SUGAR ALCOHOLS; REDUCTION PRODUCTS Sugar Alcohols are obtained by reduction of Monosaccharides (Both Aldoses and Ketoses) and disaccharides. Sugar alcohols, also known as Polyols, Polyhydric Alcohols, or Polyalcohols. SUGAR ALCOHOLS ARE THE HYDROGENATED FORMS OF THE ALDOSES OR KETOSES H- C=O + H2 H-C-OH OH-C-H H-C-OH H-C-OH CH2OH Glucose CH2OH H-C-OH OH-C-H H-C-OH H-C-OH CH2OH Sorbitol Sugars with their Corresponding Alcohols Glyceraldehyde & Dihydroxyacetone Glucose Mannose Fructose Galactose Ribose Erythrose Xylose Lactose Maltose Glycerol Sorbitol (Glucitol) Mannitol Sorbitol & Mannitol Dulcitol Ribitol Erythritol Xylitol Lactitol Maltitol Sugar Phosphates Phosphate Esters formed by various Monosaccharides are of Great Importance in Metabolic Reactions. Sugar phosphates of biological importance. Ribose and Deoxyribose in Nucleic Acids are Phosphate Esters of these monosaccharides. Phosphates of Glucose, Fructose and Glyceraldehyde etc. are important intermediate compounds in carbohydrate metabolism of almost all the cells. DISACCHARIDES Two Joined Monosaccharides. Sucrose: Glucose + Fructose Maltose: Glucose + Glucose Lactose: Glucose + Galactose OLIGOSACCHARIDES Composed Of: Three To Ten Monosaccharide Units. E.g. Fructooligosaccharides POLYSACCHARIDES Larger Than Ten Monosaccharide Units. Can Reach Many Thousands Of Units. Homopolysaccharides. Heteropolysaccharides. HOMOPOLYSACCHARIDES Similar Types of Monosaccharide Units. Starch Glycogen Cellulose HETEROPOLYSACCHARIDES Different Types of Monosaccharide Units. Mucopolysaccharides (Glycosaminoglycans that contain galactose and amine sugars) Agar (Contains various sugars like Glucose, Galactose)