Biochemistry: Carbohydrate Chemistry PDF

# Carbohydrate (CHO) Chemistry ## Definition - Carbohydrates are organic compounds that: - Contain: (CHO). - Carbon - Hydrogen - Oxygen - Contains more than one "OH" group - Contains free active carbonyl group - Either aldehyde (HC=O) or ketone (C=O) group...

# Carbohydrate (CHO) Chemistry ## Definition - Carbohydrates are organic compounds that: - Contain: (CHO). - Carbon - Hydrogen - Oxygen - Contains more than one "OH" group - Contains free active carbonyl group - Either aldehyde (HC=O) or ketone (C=O) group ## Why we study CHO - CHO is the primary source for production of energy for tissues e.g., brain, muscles and erythrocytes. ## Classification of Carbohydrates - They are classified according to the number of sugar units into: | Carbohydrate | Description | |---|---| | **I. Simple carbohydrates** | | | **1- Monosaccharides** | 1 sugar unit | | | Glucose, fructose, galactose | | **2- Disaccharides** | 2 sugar unit | | | Maltose, sucrose, lactose | | **3- Oligosaccharides** | 3-10 sugar units | | | Raffinose, sesamose | | **II. Complex carbohydrate** | | | **Polysaccharides** | > 10 sugar units | | | Starch, glycogen, fibers | ### I. Simple carbohydrates #### 1- Monosaccharides ##### Definition - They are the simplest sugar: 1. Formed of one sugar unit 2. Cannot be hydrolyzed into smaller unit #### Types and Biological importance of monosaccharides | Type | Biological importance | |---|---| | 1- Glucose| | (Dextrose | | or Grape | | Sugar) | 1. Principal famous sugar in the blood. | 2. primary source for energy for tissues e.g., brain and erythrocytes. | 3. Ingested carbohydrates are absorbed in the form of glucose. | 4. It can convert to other sugars like galactose, lactose, fructose, glycogen. | | 2- Fructose | 1. It is the sugar of seminal plasma (sperms utilize fructose for energy production). | 2. it enters in the formation of: - a) disaccharide sucrose - b) polysaccharide inulin | | 3- Galactose | It enters in the formation of: | a) Lactose (milk sugar): in mammary gland | b) Galactolipids & glycoproteins. | | 4- Pentoses| | (Ribose) | Enter in the formation of: | a) Nucleic acids: RNA | b) Energy compound: ATP. | c) Co-enzymes: NAD & NADP | d) 2nd messenger: CAMP | e) Vitamins: riboflavin | | 5- Mannose | Enter in the formation of glycoproteins | #### Monosaccharide’s derivatives ##### 1- Sugar acids: Due to Oxidation of monosaccharides - **A. Aldonic acids** - Oxidation of the carbonyl group to carboxylic group yields Aldonic (eg. gluconic acids) - Used as specific test to measure amount of glucose in urine and blood. - **B. Uronic acids** - Oxidation of the last carbon yields uronic (eg.D glucuronic acid) - Glucuronic acid is used in: - 1. Formation of mucopolysaccharides - 2. Conjugation of bilirubin, steroids, and toxic substances. ##### 2- Sugar alcohols: formed by reduction of the monosaccharides, eg: 1. Glucose → sorbitol. 2. Mannose → mannitol. 3. Fructose → sorbitol or mannitol #### 3- Deoxysugars: - They are monosaccharides with only one hydroxyl groups replaced by hydrogen - i.e., there is only one oxygen missed - e.g., 2-Deoxy-D-ribose which is a constituent of DNA. #### 4- Amino sugars: - The hydroxyl group is replaced by an amino group at the C-2 position. - Amino sugars are found in glycosaminoglycans & glycoproteins (Glucosamine, Galactosamine, and Monoamine. ### 2- Disaccharides #### Definition - Disaccharides consist of 2 monosaccharide units joined by an O-glycosidic bond. #### Classification | Disaccharide | Description | |---|---| | **Homodisaccharides** | formed of the same monosaccharide e.g., maltose, isomaltose & cellobiose. | | **Heterodisaccharides** | formed of different monosaccharide units e.g., sucrose and lactose | | | The most abundant disaccharides are sucrose, maltose, and lactose. | ##### 1. Homodisaccharides | Disaccharide | Description | |---|---| | Maltose (malt sugar) | Two a-glucose units | | | a 1-4 glycosidic | | | Reducing sugar | | | From starch by the action of amylase enzymes | | Isomaltose | Two a-glucose units | | | a 1-6 glycosidic | | | Reducing sugar | | | Hydrolysis of some polysaccharides such as dextran. | | Cellobiose | Two units β D-glucopyranose | | | β 1-4 glycosidic | | | Reducing sugar | | | Acid hydrolysis of cellulose | ##### 2. Heterodisaccharides | Disaccharide | Description | |---|---| | Sucrose | a-glucose and β-fructose | | | a-1- B-2 glycosidic bond (Involving the anomeric Cs) | | | non reducing sugar | | | (No free active carbonyl group) | | | Fruits and vegetable | | | Lactose (milk sugar)| | | B-galactose and B-glucose | | | β (1-4) link with free anomeric C. | | | It is a reducing sugar | | | (presence of free active carbonyl group) | | | principal carbohydrate in milk | ## II. Complex carbohydrates ### 3- Polysaccharides: #### Definition: - Polysaccharides (glycans), consist of more than 10 monosaccharide units and/or their derivatives joined together by glycosidic linkage. #### Classification ##### I. Homopolysaccharides (homoglycans): #### Definition: - Polysaccharides that contain only one type of monosaccharide. E.g., starch, glycogen, dextrin, cellulose, inulin #### Example: 1. Starch - It is a glucosan (formed of a-D glucose units) - consists of 2 layers: - Inner linear non branching layer called amylose. - Outer highly branched layer called amylopectin. - It is the most common storage polysaccharide in plants - Acts as a basic source of energy - Its partial hydrolysis gives Dextrin (polysaccharides) used as mucilage and in infant feeding 2. Glycogen (animal starch) - Several a-glucose units linked by a 1-4 linkage, and the link a 1-6 at the branching point - Major Major form of storage polysaccharides in animals and human - Humane store glycogen in: - a) Liver (10% of its mass) (during fasting liver hydrolyze its glycogen and release glucose to maintain normal blood glucose level - b) Muscle (1-2% of its mass) 3. Cellulose - Formed of Several β-D-glucose units. - Human body cannot hydrolyze cellulose due to absence of β glucosidase enzyme→ undigested cellulose increase bulk of food in intestine→ increase peristalsis→ prevent constipation. ### III. Heteropolysaccharides #### Definition: - Polysaccharides that contain more than one type of monosaccharides. E.g., glycosaminoglycans (GAGs, mucopolysaccharides), #### Other names: =Glycosaminoglycans (GAGs) =Mucopolysaccharides #### Structure of GAGs: - long linear unbranched chains composed of repeating disaccharide units (sugar acids-amino sugar) 1. The amino sugar: either D-glucosamine or D-galactosamine) 2. The sugar acid: either glucuronic or L- iduronic #### Types of Heteropolysaccharides (GAGS) | Type | Site | Main function | |---|---|---| | 1-Heparin | Intracellular granules of mast cells lining the arteries | Anticoagulant | | 2-Heparan sulfate | Extracellular GAG, components of cell surfaces | Component of cell surface | | 3-Hyaluronic acid | synovial fluid of joints | lubricant and shock absorbent | | 4-Keratan sulfate | Cornea, cartilage | | | 5-Chondroitin sulfate | Cartilage, tendons, ligaments, bone, | Protective and supportive | | 6-Dermatan sulfate | Skin, bone, blood vessels | | ## IV. Clinical applications of carbohydrates Chemistry ### Lactose Intolerance (Lactase Deficiency) - Lactose (a disaccharide) is the principal carbohydrate in milk - It is hydrolyzed by the intestinal lactase enzyme into glucose and galactose - Low or absence of lactase enzyme leads to undigested lactose that undergoes bacterial fermentation in the colon with the generation of large amounts of CO2, H2 and irritating organic acids. - These products cause painful digestive upsets such as bloating, gases, and diarrhea, about 30 minutes to two hours after ingesting milk or other dairy products containing lactose. - This condition is known as lactose intolerance. - People who are lactose intolerant may need to avoid eating these products or take medicines containing the lactase enzyme before doing so. - **Lactose Tolerant (has lactase)** - small intestine - large intestine - **Lactose Intolerant (no lactase)** - small intestine - large intestine