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Carbohydrates Part 1: Introduction & Monosaccharides What Is The

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Carbohydrates Part 1: Introduction & Monosaccharides What Is The Carbohydrates Part 1: Introduction & Monosaccharides Carbohydrates are polyhydroxyaldehydes, polyhydroxyketones, or compounds that yield them after hydrolysis. Video Error Circle the aldehyde or ketone in each structure below. Correction O This ketohexose is CH CH2OH D-sorbose, NOT H COH C O D-fructose as stated HO CH H COH in the video. H COH HO CH H COH H COH CH2OH CH2OH classification classification What is the molecular formula for each structure above? Hypothesize the origin of the term carbohydrate. Carbohydrate Vocabulary & Classification Carbohydrates are classified by the number of simple sugars bonded together. Monosaccharides Disaccharides Oligosaccharides Polysaccharides Aldose Ketose Pentose Hexose The terms aldose, ketose, pentose and hexose can be mixed to describe sugars (carbohydrates). Use these terms to characterize the two monosaccharides at the top of this page. Monosaccharides - Cyclic Structure Simple 5- and 6-carbon sugars can react with themselves to make cyclic structures. There are several ways to show cyclic monosaccharides. Fischer Projection Haworth Projection Chair Conformation CHO H OH HO H H OH H OH CH2OH D–glucose -D-glucopyranose -D-glucopyranose Sugars exist almost exclusively as five and six-membered rings that include 1 oxygen atom in the ring so they are named after furan and pyran. OH HO O CH2OH H O H H HO H OH H H OH HO OH OH H HOH 2 Anomeric Carbons: carbon atoms that are bonded to two different oxygen atoms in a carbohydrate The anomeric carbon gets the lowest possible number. Anomeric Carbons – two orientations -anomer: -anomer: D-glucose D-glucose Are the anomeric carbons chiral? 3 Mutarotation: a pure form of an or β carbohydrate is converted to a mixture of the two forms Point an arrow to the anomeric carbons in the structures above. Simple sugars are constantly converting back and forth from the open chain to the closed ring. The furanose and pyranose names are frequently omitted from the sugar name, because it is assumed that we all know sugars are primarily found in their cyclic form. 4 Monosaccharides to Know Glucose - the most widely occurring monosaccharide. D-glucose is a source of energy to fuel biochemical reactions. Fischer Projection Haworth projection (-D-glucose) Galactose - the widely distributed in plant gums and pectins and is found in milk sugar (the disaccharide lactose). It is also synthesized in the body from glucose as a component of glycolipids & glycoproteins. Fischer Projection Haworth projection (-D-galactose) 5 Monosaccharides to Know Fructose - found in honey, fruit, table sugar (the disaccharide sucrose), and sweeteners (high fructose corn syrup). Fischer Projection Haworth projection -D-fructose Modified Monosaccharides Ribose & Deoxyribose – These two sugars are found in biomolecules such as ATP, coenzyme A, & nucleic acids (DNA & RNA). Other Modified Monosaccharides found in the fluids that lubricate joints O - CH OH C O 2 CH2OH CH2OH OH OH OH OH O O O O OH OH OH OH O HO HO HO HO OH OH NH2 NH CCH3 -D-glucose -D-gluconate -D-glucosamine N-acetyl--D-glucosamine 6 Carbohydrates Part 2: Stereochemistry of Monosaccharides Glyceraldehyde – the simplest sugar What is the relationship between the two possible structures for glyceraldehyde? Note: 1) Most common sugars of biological significance have the D configuration. 2) Fischer Projections – another way to show stereochemistry Star each chiral carbon in the following common sugars. Enantiomers: non-superimposable mirror images Diastereomers: non-superimposable stereoisomers that are NOT mirror images What is the relationship between the L & D isomers of fructose? What is the relationship between D-glucose & D-galactose? What is the relationship between D-glucose & D-fructose? Carbohydrates Part 3: Disaccharides & Glycosidic Bonds Glyco- is a prefix used to indicate the presence of sugars in biological molecules Glycosidic bonds link monosaccharides into disaccharides, oligosaccharides, and polysaccharides or link saccharides to other biological molecules through their hydroxyl groups. Glycosidic bonds always form between the anomeric carbon of the sugar on the left and the hydroxyl group of another sugar or biological molecule on the right. Glycosidic bonds are classified by the configuration of the anomeric carbon (α or β) and the location of the other hydroxyl group. Practice Classifying Glycosidic bonds of these Disaccharides Maltose Lactose Sucrose Reducing Sugars Not all sugar rings can open. Only the anomeric carbons that are bonded to one hydroxyl group can open. Anomeric carbons bonded to two ether groups are locked closed. CHO H OH HO H H OH H OH CH2OH Identify which of the following rings can open. Find the anomeric carbons and draw arrows to the glycosidic bonds in the compounds below. When the ring can open the sugars can be oxidized, and the sugars are described as reducing sugars in the same way we use the term reducing agent. Which of the sugars above are reducing sugars? O O H OH H OH Benedict's reagent H OH HO H 2+ + Cu HO H + Cu2O H OH H OH H OH H OH CH2OH CH2OH 2 Name the two monosaccharides below. Draw each monosaccharide in its β form using a Haworth projection. Draw the disaccharide formed by a β-(1,4) glycosidic bond using Haworth projections. Is the resulting disaccharide a reducing sugar? O O H H H OH H OH HO H + HO H H OH HO H H OH H OH CH OH CH2OH 2 3 Carbohydrates Part 4: Polysaccharides Polysaccharides are polymers containing > 100 monosaccharides. They are not soluble in water but their many hydroxyl groups become hydrated and form thick suspensions. Important Polysaccharides to know Starch & Glycogen vs Cellulose Starch is comprised of amylose and amylopectin. Carbohydrates Part 5: Catabolism Stage 1 (Hydrolysis) & Stage 2 (Glycolysis) An overview of catabolism Stage 1 - Hydrolysis The 1st stage of carbohydrate catabolism is digestion – the breakdown into small molecules for energy production. Digestion begins in the mouth with the physical grinding, softening and mixing of food. Salivary α-amylase catalyzes the hydrolysis of the glycosidic bonds in carbohydrates. α-amylase is denatured in the stomach. Further digestion occurs in the small intestine where additional α-amylase is secreted by the pancreas along with maltase, sucrase and lactase from the mucous lining of the small intestine. Stage 2 – Glycolysis The conversion of glucose to pyruvate. Stage 3 – Acetyl CoA enters Citric Acid Cycle to produce CO2 & reduced coenzymes. The reduced coenzymes transport the electrons to the electron transport chain (ETC) which ultimately reduces O2 to H2O and drives the formation of ATP from ADP & P1 in a process known as oxidative phosphorylation. Stage 1 Hydrolysis of polysaccharides (starch, corn syrup & high fructose corn syrup) breaking the glycosidic bond with water & enzymes Hydrolysis of Disaccharides breaking the glycosidic bond with water & enzymes H2O maltase Draw the reaction for sucrose hydrolysis using Haworth projections. Name the products. 2 Stage 2 - Glycolysis Look through the sequence of reactions in glycolysis and classify the enzymes (Hydrolase, Lyase, Ligase, Transferase, Isomerase, or Oxidoreductase) needed to catalyze each reaction. 3 Fate of Pyruvate A lack of oxygen will slow down electron transport, causing a build-up In the mitochondrial matrix, of NADH and decreasing the amount pyruvate is oxidized to form carbon of NAD+ available for glycolysis. If dioxide and an acetyl group (acetyl– there is no NAD+, glycolysis cannot CoA). continue. The reduction of pyruvate to lactate will generate the NAD+ needed Pyruvate must diffuse into the for glycolysis (step 6). mitochondria from the cytosol. It is then transported by a membrane protein across the inner mitochondrial membrane into the matrix. Tissues with low oxygen content (such What happens to the acetyl-CoA? as skeletal muscle) rely on anerobic production of ATP by glycolysis. Some bacteria can convert pyruvate to lactate under anaerobic conditions. The preparation of kimchee, sauerkraut, and yogurt involve these types of bacteria. Yeast converts pyruvate to ethanol and CO2 under anaerobic conditions. 4 Carbohydrates Part 6: Other Metabolic roles of Glucose & Ketone Bodies Glycogenesis: synthesis of glycogen from glucose Glycogenolysis: Degradation of glycogen to produce glucose Gluconeogenesis: Breakdown of proteins; in the liver, formation of glucose from amino acids Glycolysis: breakdown of glucose to pyruvate Regulation of Glucose Metabolism and Energy Production Two hormones secreted by the pancreas play a major role in glucose metabolism. Metabolism during Fasting or Starving Gradual decline in blood glucose triggers the catabolism of lipids causing a build-up of acetyl CoA. Ketone bodies form from the excess acetyl CoA. (see rxn below) Brain and other tissues catabolize ketone bodies to produce ATP. Diabetes Mellitus - glucose cannot be utilized or stored as glycogen because insulin is not secreted or does not function properly, therefore, insufficient amounts of glucose are present in tissues. Liver cells synthesize glucose from non-carbohydrate sources (gluconeogenesis) and break down fat. Acetyl-CoA builds up and ketone bodies accumulate (ketosis). Glucose appears in the urine because it is not undergoing glycolysis. Formation of Ketone Bodies from Acetyl CoA If the concentration of ketone bodies becomes too high, as can happen in diabetics or on a very low carbohydrate diet, a condition called ketoacidosis can result. Since the ketone bodies are not completely metabolized, acetone can diffuse out of the bloodstream into air in the lungs. The acetone can be smelled on the breath. Also, since ketone bodies acetoacetate and β-hydroxybutyrate are acidic, the pH of the blood decreases. This affects the ability of the hemoglobin to carry oxygen – breathing can become difficult. Untreated, ketoacidosis can lead to coma or death. 2 .
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