Chapter 5 – An Introduction to CarbohydratesWhat is a carbohydrate? - All carbohydrates are variations of (CH2O)n, where n is the number of “carbon-hydrate” groups- All Carbohydrates contain a carbonyl group and several hydroxyl groups- Carbohydrates perform a wide variety of functions in cells: - serving as raw material for synthesizing other molecules  “building blocks”- providing structural support carbohydrates play a major structural role in all plants and in some animals - indicating cell identity- storing chemical energy.I. Sugars as Monomersa. How monosaccharides differ:i. Monosaccharides (simple sugars) are the monomers of carbohydratesii. The carbonyl group can be at the end (aldose) or in the middle (ketose)iii. Monosaccharides can have three, five, or six carbons (trioses, pentoses, and hexoses, respectively)iv. They can vary in the spatial arrangement of their –OH groups  Epimersv. They can take a linear form or a ring shape  Muta rotation? α and β?II. The Structure of Disaccharides and Polysaccharidesa. A polysaccharide, or complex carbohydrate, is a polymer ofcovalently linked monosaccharidesb. 2 Monomers are joined by glycosidic linkages between –OHgroups (-OH group on anomeric C of one monosaccharide alwaysinvolved)  Disaccharide β 1 4 linkage shown here. Why β?c. Glycosidic linkages can form in several different locations, resulting in different geometries and different properties. Examples: α- and β-linkages and the anomeric Cd. Starch: a storage polysaccharide in plantsi. Starch consists of α-glucose monomers joined by α -1  4 glycosidic linkagesii. Starch is a mixture of unbranched amylose and branched amylopectine. Glycogen: a highly branched storage polysaccharide in animals (more branched than in starch)i. Like starch, glycogen consists of α-glucose monomers joined by α-1  4 glycosidic linkagesii. Glycogen is more highly branched than starchf. Cellulose: a structural polysaccharide in plantsi. Cellulose is a major component of plant cell wallsii. Cellulose consists of β-glucose monomers joined by β-1,4-glycosidic linkagesiii. Every other glucose is flipped, which allows H bonds between strands. This makes cellulose fibers ( parallel strands) straight and strongg. Chitin: a structural polysaccharide in fungi and crabs, lobsters an shrimpi. Chitin stiffens the cell walls of fungi and some algae and is an important component of the exoskeletons of insects and crustaceansii. Chitin has β-1,4-glycosidic linkages between N-acetylglucosamine monomers1iii. Like cellulose, every other chitin monomer is flipped, allowing for the formation of H bonds and making a strong, tough sheeth. Peptidoglycan: a structural polysaccharide in bacteria. i. Peptidoglycan strengthens the cell walls of bacteriaii. It has two different monosaccharides joined by β-1,4-glycosidic linkagesiii. The structural polysaccharides have a similar structure. They are long, straight, parallel strands that are H-bonded to each other, which makes them strong. The glycosidic linkage is β. Monosaccharides    Polysaccharides↓ glycosidic linkages. ↓Glucose, Galactose Starch, Glycogen(deoxy)Ribose, Mannose, Fructose Cellulose, ChitinPeptidoglycanIII. What Do Carbohydrates Do?a. Carbohydrates are the raw materials for synthesizing more complex molecules-Both RNA and DNA contain sugars-Amino acids are also produced from sugarsb. Structural supporti. Cellulose, chitin, and peptidoglycan form strong fibers that cross-link to form tough sheets that provide strength and elasticityii. These polysaccharides are resistant to degradation because most organisms do nothave enzymes that can break β-1,4-glycosidic linkagesc. Cell identityi. A protein with a covalently linked carbohydrate group is aglycoproteinii. Glycoproteins are key molecules for cell recognition andcell signalingiii. Each cell carries a set of glycoproteins or glycolipids on its cell surface, identifying it as part of that body and also identifying its tissue type (nervous, muscle, etc.)  PIN # for the cell!iv. The diversity of monosaccharides allows many unique glycoproteins to existd. Energy storage-Carbohydrates store energy from sunlight as chemical energy in its chemical bonds.-Energy from the sun is stored in the bonds of carbohydrates via the process of photosynthesis: CO2 + H2O + sunlight  (CH2O)n + O2-During photosynthesis, electrons are moved from C-O and C=O bonds (in carbon dioxide and water) to C-C and C-H bonds (in carbohydrates)a. C-C and C-H bonds have higher potential energy than C-O and C=O bondsb. Carbohydrates are more highly ordered than carbon dioxide and waterc. Overall, carbohydrates have much higher free energy than carbon dioxide and water- Organisms can further break down the carbohydrate monomers to carbon dioxide and water, capturing the released energy in ATP: [CH2O]n + O2 + ADP + Pi  CO2 + H2O + ATP2- Energy stored in glucose is transferred to ATP: The free energy in the bonds of carbohydrates istransferred to the phosphate bonds of ATP, which can drive endergonic reactions in the cell.ATP = Cellular Energy