L8 Carbohydrate Chemistry PDF

Carbohydrates  Carbohydrates (CHO) Carbohydrates are organic hydrocarbon molecules (Carbon & Hydrogen & Oxygen) Carbohydrates are important for: 1- Source of energy through catabolic pathways 2- Store energy in the form of: a- starch (in plants) b- Glycogen (in...

Carbohydrates  Carbohydrates (CHO) Carbohydrates are organic hydrocarbon molecules (Carbon & Hydrogen & Oxygen) Carbohydrates are important for: 1- Source of energy through catabolic pathways 2- Store energy in the form of: a- starch (in plants) b- Glycogen (in animals and humans) 3- Supply carbon for synthesis of protein and fat. 4- structure of nucleic acids e.g DNA (Deoxy-ribose) and RNA (Ribose). Classification of carbohydrates  ?What is a monosaccharide -They are the simplest CHO that have polyhydroxy aldehydes or ketones with the formula (C-H2-0)n -Those with three carbons are called trioses; four, tetroses; five, pentoses; and six, hexoses. -They are called aldoses or ketoses, depending on functional group is an aldehyde or a ketone. Classification of monosaccharides Steroisomers (epimers ,enantiomers ,anomers) Asymmetric C atom: carbon that attached to 4 different groups or atoms. Ex: Glucose contains 4 asymmetric carbon atoms Stereoisomers have the same chemical formula but differ in the position of the hydroxyl groups on one or more of their asymmetric carbons. 1.Enantiomers are stereoisomers that are mirror images of each other eg, D glucose and L glucose 2.Epimers are stereoisomers that differ in the position of the hydroxyl group at only one asymmetric carbon. eg, D-glucose and D-galactose are C4 epimers Cyclization of monosaccharides  Sugar derivatives Sugar alcohol : aldehyde or ketone group-1.is reduced to hydroxyl group Example : Sorbitol is formed from excess glucose and accumulates in eye and nervous tissues causing cataract and neuropathy. 2-Sugar acid : aldehyde group, or the hydroxyl on the terminal carbon , is oxidized to carboxylic group. Examples: are gluconic acid and glucuronic acid. Glucuronic acid is involved in drug metabolism via conjugation. Amino sugar :formed by replacement of OH-3 group by amino Group. An example is. glucosamine  Disaccharides Monosaccharides can be joined by glycosidic bonds to form disaccharides (two units) oligosaccharides (3-10 units) polysaccharides (more than 10 units) The bonds that link monosaccharides are called glycosidic bonds Important Disaccharides: 1. Lactose (galactose +glucose): found in milk 2. Sucrose (glucose + fructose): found in table sugar 3. Maltose (glucose + glucose): in malt 4. Lactulose (galactose + Fructose): synthetic used as laxative and ammonia removal from GIT (non digestible non absorbable)  Reducing Sugars If anomeric carbon (active group: aldehyde or keto) of a sugar is free, the sugar can act as a reducing agent and is termed a reducing sugar. :Medical Importance These sugars can react with Benedict's reagent or Fehling's solution causing the reagent to be reduced and colored Applications in Medicine: Diagnosis of presence glucose in diabetic patient and lactose in lactating female in urine :Reducing and non-reducing sugars All monosaccharides are reducing sugars - All disaccharides (EXCEPT sucrose) are reducing sugars - Oligo- and polysaccharides are non-reducing sugars -  Simple (Homo)Polysaccharides 1- Glycogen:- It is a long and branched polysaccharide (glucose polymer) that humans and animals store in the liver and skeletal muscles. - Main storage of carbohydrates in the body 2- Starch.It is available in plants - It is the main carbohydrate of diet - -.Rich sources of starches: include potatoes, rice and wheat - - It is a polysaccharide (glucose polymers) made up of: amylose (inner layer of starch granules) -1 molecules are linear (long but with no branches) amylopectin (outer layer of starch granules) -2 molecules are long and with branches Glycogen & Amylopectin of Starch are branched chain polysaccharides made from a- D- glucose. Glucose molecules are bound by a (1 - 4) linkage Branches are linked by a(1 - 6) linkage Humans and animals digest starch by hydrolysis by the enzyme amylase 3- Cellulose the structural constituents of plants are made mainly from cellulose. Fibers of vegetables & fruits are cellulose. Some animals can digest cellulose because their gut has a type of bacteria that has an enzyme which breaks down cellulose. BUT humans can not digest cellulose  Complex (Hetero) Carbohydrates Carbohydrates can be attached by glycosidic bonds to non-carbohydrate molecules : 1- Purines and pyrimidines (in nucleotides of nucleic acids) 2- Proteins (in glycoproteins and proteoglycans ) 3- Lipids (glycolipids)