Carbohydrates PDF

CARBOHYD RATES  INTRODUCTION  Carbohydrates are one of the four major classes of biomolecules, along with proteins, lipids, and nucleic acids.  The term "carbohydrate" is derived from the words "carbon" and "hydrate," reflecting their basic composition, which consists primar...

CARBOHYD RATES  INTRODUCTION  Carbohydrates are one of the four major classes of biomolecules, along with proteins, lipids, and nucleic acids.  The term "carbohydrate" is derived from the words "carbon" and "hydrate," reflecting their basic composition, which consists primarily of carbon (C), hydrogen (H), and oxygen (O) atoms, often in a ratio of 1:2:1 (C:H:O).  MONOSACCHARIDES Monosaccharides are the simplest form of carbohydrates that cannot be hydrolyzed into smaller carbohydrates. They are the basic building blocks of more complex carbohydrates such as disaccharides, oligosaccharides, and polysaccharides. Their general chemical formula is CnH2nOn, where "n" is typically between 3 and 7. They are categorized based on the number of carbon atoms and the functional group present.  CLASSIFICATION  BY THE NUMBER OF CARBON ATOMS Trioses (3 carbons): e.g., Glyceraldehyde. Tetroses (4 carbons): e.g., Erythrose. Pentoses (5 carbons): e.g., Ribose. Hexoses (6 carbons): e.g., Glucose, Fructose, Galactose.  CLASSIFICATION  BY THE TYPE OF CARBONYL GROUP Aldoses: Monosaccharides that contain an aldehyde group (-CHO). Example: Glucose is an aldose because it has an aldehyde group at the end of the molecule. Ketoses: Monosaccharides that contain a ketone group (C=O). Example: Fructose is a ketose because it has a ketone group at the second carbon. CYCLIC STRUCTURES In aqueous solution, monosaccharides with 5 or more carbon atoms form cyclic (ring) structures. PYRANOSE RING FURANOSE RING  DISACCHARIDES Disaccharides are carbohydrates composed of two monosaccharides linked by a glycosidic bond. They are formed through a condensation reaction, where a molecule of water is released when the bond forms between two sugar molecules.  TYPES Sucrose (C12H22O11) with lactose intolerance lack lactase. Lactose (C12H22O11) Maltose (C12H22O11) Monosaccharides: Glucose + Fructose. Monosaccharides: Glucose + Monosaccharides: Two Glucose units. Galactose. Commonly known as table sugar. Known as malt sugar. Known as milk sugar. It is the most prevalent disaccharide in Formed during the breakdown of starch the diet and is found in sugar cane, Found in milk and dairy products. (e.g., in the malting of grains). sugar beets, and many fruits. Glycosidic Bond: α-1,4-glycosidic Glycosidic Bond: α-1,2-glycosidic bond between two glucose molecules. bond between glucose and fructose. Glycosidic Bond: β-1,4-glycosidic bond between glucose and galactose. Digestion: Hydrolyzed by the enzyme maltase. Digestion: Hydrolyzed by the enzyme sucrase in the small intestine. Digestion: Hydrolyzed by the enzyme lactase in the small intestine. People  POLYSACCHARIDES Polysaccharides also called glycans, are large, complex carbohydrates composed of many monosaccharide units (simple sugars) linked together by glycosidic bonds. Polysaccharides can consist of hundreds to thousands of monosaccharide units and can be classified into two main categories: storage polysaccharides and structural polysaccharides.  STARCH Plant Storage Polysaccharide It consists of two components: o Amylose – A linear chain of glucose molecules connected by alpha-1,4-glycosidic bonds. o Amylopectin – A branched structure with both alpha-1,4-glycosidic bonds and alpha-1,6- glycosidic bonds at branching points. Starch is stored in plant tissues such as roots, tubers, and seeds (e.g., potatoes, rice, corn). When needed, starch can be broken down into glucose by enzymatic processes like amylase.  GLYCOGEN Animal Storage Polysaccharide Structure Polymer of glucose with (α1→4) linkages and (α1→6) branches. Branching: More extensively branched than amylopectin (branches every 8 to 12 residues). Compactness: More compact structure than starch. Primary Storage: Liver (up to 7% of wet weight) and skeletal muscle. Function: Provides a rapid energy source by releasing glucose from non-reducing ends (via degradative enzymes).  CELLULOSE Cellulose is the most abundant organic polymer on Earth. Found in the cell walls of plants. It is composed of long chains of beta-glucose units linked by beta-1,4-glycosidic bonds. These chains form hydrogen bonds between neighboring molecules, providing high tensile strength and rigidity to the plant cell wall. Cellulose is indigestible by most animals, including humans, due to the lack of the enzyme cellulase, which breaks down the beta-glycosidic bonds. However, some herbivores, such as ruminants, have microorganisms in their digestive systems that can break down cellulose.  DEXTRANS Bacterial and Yeast Polysaccharides Structure Made of (α1→6)-linked poly-D-glucose. Branches: Contain (α1→3) branches; some also have (α1→2) or (α1→4) branches. Occurrence: o Dental Plaque: Rich in dextrans formed by bacteria on teeth surface. o Synthetic Dextrans: Used in size-exclusion chromatography (Sephadex) for protein fractionation. Applications Used in commercial products for separating macromolecules by size.  CHITIN Chitin is a structural polysaccharide found in the exoskeletons of arthropods (insects, crustaceans) and the cell walls of fungi. It is composed of N-acetylglucosamine (GlcNAc) units linked by beta-1,4-glycosidic bonds. Chitin provides rigidity and protection. It is also used in various industrial applications, including the production of biodegradable plastics and wound dressings. PEPTIDOGLYCAN, AGAR & CARRAGEENAN Peptidoglycan is a structural polysaccharide found in the cell walls of bacteria. It is made up of repeating disaccharide units consisting of N-acetylglucosamine (GlcNAc) and N- acetylmuramic acid (MurNAc), linked by peptide bridges. Peptidoglycan provides strength to the bacterial cell wall and helps protect the cell from osmotic pressure. Agar is a polysaccharide extracted from red algae. It is used in laboratory applications for solidifying culture media. It consists of repeating units of agarose and agaropectin. Carrageenan is another polysaccharide derived from red algae Commonly used as a thickening agent in the food industry. It contains repeating units of sulfated galactose sugars. Property Starch Glycogen Cellulose Dextran Source Found in plants (e.g., Found in animals (e.g., liver, Found in plants (e.g., wood, Produced by bacteria and yeast. potatoes, corn, rice). muscles). cotton). Monomer D-glucose D-glucose D-glucose D-glucose Glycosidic (α1→4) for amylose, (α1→4) for main chain, (α1→6) for main chain, Linkages (α1→6) for amylopectin (α1→6) for branches (β1→4) (α1→3), (α1→2) for branches Branching Amylose: unbranched; Highly branched No branching (linear) Branched Amylopectin: branched (every 8–12 residues) Solubility in Water Soluble (amylose) or Soluble in water partially soluble (amylopectin) Insoluble in water Insoluble in water (due to branched structure) Structural component in plant Used by bacteria for adhesion, Function Energy storage in plants Energy storage in animals cell walls also used in chromatography Storage Form Stored in plants as starch Stored in animals as glycogen Not stored (structural Stored by bacteria in slime or granules granules component in cell walls) extracellular polysaccharide matrix Abundant in seeds, tubers, Abundant in liver and muscles Found in plant cell walls (cotton, Found in bacterial biofilms, dental Occurrence and fruits of animals wood, etc.) plaque, and some fungi  FUNCTIONS Structural Cellular Energy Source Components Communication Metabolic Protective Regulation Functions  METABOLISM Digestion: Begins in the mouth with salivary amylase breaking down starch. Continues in the small intestine with pancreatic amylase. Absorption: Monosaccharides are absorbed in the small intestine and transported to the liver via the portal vein. Pathways: Glycolysis: Breakdown of glucose to pyruvate. Gluconeogenesis: Formation of glucose from non-carbohydrate precursors. Glycogenesis: Synthesis of glycogen. Glycogenolysis: Breakdown of glycogen to glucose.  DISORDERS Diabetes Mellitus Lactose Intolerance Glycogen Storage Diseases CARBOHYDRATE DETECTION TESTS Test Purpose Molisch's Test Detects all carbohydrates. Benedict's Test Detects reducing sugars. Fehling's Test Detects reducing sugars. Iodine Test Detects starch. Seliwanoff's Test Differentiates aldoses and ketoses. Barfoed's Test Distinguishes monosaccharides from disaccharides. Tollens’ Test Detects reducing sugars (mainly aldehydes).