Carbohydrates Chemistry PDF

1 Carbohydrates Chemistry Dr. Dalia Mahmoud Dr. Amal Darwish Lecturers of Medical Biochemistry And Molecular Biology  Carbohydrate Chemistry Carbohydrates are organic compounds composed of C, H, O. They generally have the common formula (CH2O)n, w...

1 Carbohydrates Chemistry Dr. Dalia Mahmoud Dr. Amal Darwish Lecturers of Medical Biochemistry And Molecular Biology  Carbohydrate Chemistry Carbohydrates are organic compounds composed of C, H, O. They generally have the common formula (CH2O)n, where the least number of n = 3 They are polyhydroxy-ketones or polyhydroxy- aldehydes.  Poly OH Aldehyde & Poly OH Ketones. Aldehyde Ketones Carbohydrates may also contain nitrogen, phosphorus and sulfur  Importance of Carbohydrates 1. Main energy source. 2. Serve a structural components in cell membrane. 3. Lubrication of joints and tendons (Proteoglycans)  Importance of CHO 4. Pentose Sugars, enter in the structure of nucleotides which can form: a) Nucleic Acids (DNA, RNA). b) Coenzymes (NAD, FAD). c) Regulatory molecules (cAMP, cGMP). d) High energy compounds (ATP, GTP).  Classification of carbohydrate Carbohydrates are classified according to molecules yielded on hydrolysis into: (According to No. of sugar units) 1- Monosaccharide: 2- Oligosaccharide: 3- Polysaccharide: the simplest form of it yields from 2-10 it yields more than 10 carbohydrate which can units of units of not be hydrolyzed any monosaccharide on monosaccharide on more. hydrolysis. hydrolysis.  Classification of monosaccharides According to no. According to both of carbon atom According to (no. of atom + active sugar active sugar group group Trioses (3C) Tetroses (4C) Aldopentose (5C+ aldehyde Pentoses (5C) Aldoses (-HC=O) group) Hexoses(6C) or ketoses (C=O) Ketohexoses (6C+ Keto Heptoses(7C) group)  I- Monosaccharide According to number of carbons and active (functional) groups, monosaccharide further classified into: 1- Triose: 3 carbons 2- Tetrose: 4 carbons a- Aldo triose: e.g a- Aldo tetrose: e.g glyceraldehyde erythrose b- Keto triose: e.g b- Keto tetrose: e.g dihydroxyacetone erythrulose  I- Monosaccharide 3- Pentose: 5 4- Hexose: 6 carbons carbons a- Aldo pentose: a- Aldo hexose: e.g ribose e.g glucose, b- Keto pentose: galactose e.g ribulose b- Keto hexose: e.g fructose I- Monosaccharide Glucose serves as the essential energy source, and is commonly known as blood sugar. Fructose is the sweetest, occurs naturally in honey and fruits. Galactose rarely occurs naturally as a single sugar.  II- Oligosaccharide Type of carbohydrates is formed of 2-10 units of monosaccharide linked together by glycosidic bond. Examples: DISACCHARIDES 1- Maltose 2- Sucrose 3- Lactose  1- Maltose It is known as: Malt sugar. (‫)الشعير‬ a- Malt It is obtained b- Hydrolysis of from: starch It is formed of 2 Structure: units of glucose  2- Sucrose It is known as: Cane sugar. (‫)سكر القصب‬ formed of one glucose unit Structure: and one fructose unit  3- Lactose (Milk Sugar) Why lactose is a suitable Milk sugar Structure: Characters: sugar of milk? It is formed a- Less b- Non of one sweetly, so fermentable, glucose and Non enable baby so prevent one fermentable. to suckle colic and galactose more. distension. units  III- Polysaccharide They are further classified into: a- Homogenous b- Heterogeneous polysaccharide: polysaccharide: i- Starch i- Glycolipids ii- Glycogen ii- Glycoproteins iii- Cellulose iv- Dextrin Contain only one type of monosaccharide Contain two or more different units: monosaccharide units  1- Starch -Major storage carbohydrate in plants. It is a polymer of glucose units Formed of 2 chains a- Amylose – long straight glucose chains (non branched chain). b- Amylopectin – branched chain. It give branch every 24- 30 glucose residues. Provides 80% of dietary calories in human worldwide.  2- Glycogen Major storage carbohydrate in humans and animals. It is mainly stored in liver and skeletal muscles It is a polymer of glucose units The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise & rapidly supply glucose during fasting.  3- Cellulose A major constituent of plant cell walls, consists of long linear chains of glucose. It is non digestible, so increase bulk of stool and prevent constipation.  Digestion and Absorption of Carbohydrates Digestion: breakdown of large molecules into its simplest form (i.e Conversion of oligo and polysaccharide into monosaccharide)  Digestion and Absorption of Carbohydrates In the mouth, the salivary enzyme amylase begins to hydrolyze starch into short dextrin and maltose. The action of this enzyme stops in the stomach as the pH of the stomach is not suitable for its action. In the stomach, fiber delays gastric emptying and provides a feeling of fullness (satiety).  Digestion and Absorption of Carbohydrates o In the small intestine, pancreatic amylase hydrolyzes starch and glycogen to disaccharides and monosaccharide.  Digestion and Absorption of Carbohydrates ❑In the small intestine : Disaccharidases are secreted by intestinal cells (Sucrase, lactase, Maltase) Sucrase - Sucrose glucose and fructose. Lactase - Lactose glucose and galactose. Maltase - Maltose two glucose molecules – In the large intestine, fibers remain and attract water, soften stools and ferment.  Digestion and Absorption of Carbohydrates The end products of carbohydrates digestion are: ✓ glucose ✓ Fructose ✓ galactose They are absorbed by the small intestinal cells Glucose transporters are needed for monosaccharides absorption  Lactose Intolerance It is inability to digest milk & milk products. Symptoms include bloating, abdominal discomfort, and diarrhea. Causes: lactase deficiency due to a natural decrease that occurs with aging or damaged intestinal cells by drugs or intestinal diseases.  Lactose Intolerance management - Dietary Changes – Begin with a lactose-free diet then increase intake of milk products gradually. – Mix dairy (milk products) with other foods. – Spread dairy intake throughout the day. – Use of acidophilus milk& yogurt (fermented products). – Use of enzymes (Lactase). – Use lactose free milk  Metabolism The chemical changes that take place in a cell to produce energy and basic materials needed for important life processes.  Glucose In The Body – The body stores glucose as glycogen in liver and muscle cells. – The body uses glucose for energy if glycogen stores are available. – If glycogen stores are depleted, the body makes glucose from non carbohydrate sources – The blood glucose level of healthy individual after overnight fast ranges between 70-100mg/dl  Regulation Of Blood Glucose The Regulating Hormones Insulin (secreted from β cells of pancreas) moves glucose into the cells and helps to lower blood sugar levels. Glucagon (secreted from α cells of pancreas) brings glucose out of storage and raises blood sugar levels. Epinephrine acts quickly to bring glucose out of storage during times of stress.  Abnormal Blood Glucose Type 1 Diabetes Mellitus is the less common type with no insulin produced by the body. fasting blood glucose level is low blood Hyperglycemia >126mg/dl Type 2 Diabetes Mellitus is the glucose and can more common type where fat cells often be resist insulin. controlled by Hypoglycemia fasting blood glucose level >126mg/dl dietary changes. Prediabetes is blood glucose that is higher than normal but below the diagnosis of diabetes. fasting blood glucose level from 100 to 125 mg/dL  Type 1 Type 2 Diabetes Mellitus Diabetes Mellitus Genetic Factors Moderate Very strong Complications More common Less common Treatment Injection of Insulin Diet control Exercise Oral hypoglycemic agents Later may need insulin Recommended intake of CHO RDA for carbohydrate is 130 g per day, or 45-65% of energy intake.  Artificial Sweeteners Saccharin Aspartame Used primarily in soft drinks and as General purpose a tabletop sweetener. sweetener.