Carbohydrates Chemistry - 2 PDF

Carbohydrates chemistry - 2 Prof Dr/ Omnia Al-saied Abdullah Professor of medical biochemistry and molecular biology Benha faculty of medicine  Objectives 1. Define disaccharides and differentiate sucrose, lactose, and maltose. 2. Explain reducing vs. n...

Carbohydrates chemistry - 2 Prof Dr/ Omnia Al-saied Abdullah Professor of medical biochemistry and molecular biology Benha faculty of medicine  Objectives 1. Define disaccharides and differentiate sucrose, lactose, and maltose. 2. Explain reducing vs. non-reducing disaccharides. 3. Define polysaccharides (starch, glycogen, cellulose). 4. Introduce glycosaminoglycans (GAGs) and their biological roles. 5. Highlight the clinical importance of heparin as an anticoagulant. 6. Discuss non-digestible polysaccharides (e.g., cellulose, inulin) in dietary health. Disaccharides Disaccharides are formed by the covalent bonding of two monosaccharide units through a glycosidic bond, between the hydroxyl group (-OH) of one sugar and the anomeric carbon of the other sugar. The specific nature of the glycosidic bond (i.e., the orientation and type of bond) varies between different disaccharides.  1. Sucrose (Table Sugar) Composition: Composed of glucose and fructose. Glycosidic Bond: α(1→2) glycosidic bond: The bond is formed between the glucose α-anomeric carbon (C1) and the fructose β-anomeric carbon (C2), involving an α-linkage. 2. Lactose (Milk Sugar) Composition: Composed of glucose and galactose Glycosidic Bond: β(1→4) glycosidic bond: The glucose at C1 (β) links to galactose at C4 (in its β-configuration), forming a β(1→4) bond. 3. Maltose (Malt Sugar) Composition: Composed of two glucose units Glycosidic Bond: α(1→4) glycosidic bond: The bond is formed between C1 of one glucose unit (in the α-configuration) and C4 of the second glucose unit (α).  Summary of bonds Disaccharide Components Bond Configuration Type Sucrose Summary Glucose + ofa(1Bonds →2) Glucose (a) + Fructose Fructose (ß) Lactose Glucose + ß(1→4) Glucose (ß) + Galactose Galactose (ß) Maltose Glucose + a(1→4) Glucose (a) + Glucose Glucose (a)  Disaccharide Reducing Power Reason Reducing Power of Disaccharides : -The reducing power of a sugar Sucrose Non-reducing Both glucose and fructose anomeric refers to its ability to reduce carbons are involved another molecule due to the in glycosidic bond presence of a free aldehyde preventing any free anomeric carbon. group or ketone group in its open- chain form. Lactose Reducing Glucose unit has free -Disaccharides can be classified as anomeric carbon reducing or non-reducing based (C1). on whether one of their monosaccharide units has a free anomeric carbon (the reactive Maltose Reducing Second glucose unit carbon that is part of the reducing has free anomeric carbon (C1). group). Invert Sugar  Definition: Polysaccharides are high- molecular-weight carbohydrates composed of long chains of monosaccharide units (> 10 units) linked by glycosidic bonds. Glycosidic bonds are formed between Polysaccharides two monosaccharides when a hydroxyl group (-OH) from one reacts with the anomeric carbon of the other, releasing water. The type of glycosidic bond depends on the configuration of the anomeric carbon.  Feature Alpha Glycosidic Bond Beta Glycosidic Bond Orientation of The hydroxyl group on the The hydroxyl group on the Bond anomeric carbon points anomeric carbon points downward relative to the plane upward relative to the of the sugar ring (cis to the plane of the sugar ring CH₂OH group). (trans to the CH₂OH Alpha bonds are easier to hydrolyze, group). making them suitable for energy storage. Beta bonds are more stable and Structure of Results in more compact, Results in linear, rigid resistant to enzymatic breakdown, ideal Polysaccharides helical structures (e.g., starch structures (e.g., cellulose). for structural purposes. and glycogen). Digestibility in Readily digested by human Cannot be digested by Humans enzymes (e.g., amylase breaks human enzymes (e.g., alpha bonds in starch). beta bonds in cellulose). Examples Maltose, glycogen, starch Cellulose, lactose (amylose and amylopectin). Function Energy storage Structural support 2. Classification of Polysaccharides 2. Classification of Polysaccharides  Function in Function in Feature Location Structure Digestibility Role in Human Diet Plants Animals Starch Easily Energy Provides dietary Primary carbohydrate source. -Amylose (15-20%): carbohydrate digestible storage Linear chain of glucose with α(1→4) by humans. source bonds. Gives blue colour with iodine test. - Amylopectin (80-85%): Branched structure with α(1→4) and plant α(1→6) bonds at the branching points. Gives reddish violet colour with iodine test. Glycogen animals, Highly branched: Quick-release Stored in tissues. especially liver - α(1→4) bonds in chains. energy for -Liver Glycogen: Maintains blood glucose - α(1→6) bonds at branch points. metabolism. levels by releasing glucose into the and muscles. Easily Not present bloodstream, especially during fasting. digestible by -Muscle Glycogen: Provides energy in plants. humans. directly to muscle cells during exercise and physical activity. Cellulose Linear chains: Not Laxative: Promotes healthy bowel - Glucose units linked by β(1→4) Provides metabolized; movements by adding bulk to stool, plant cell bonds. Not digestible structural serves as dietary preventing constipation. walls. - No branching. by humans. fiber. strength. Feature Definition Source Digestibility by Chemical Bond Humans Chitin A structural Found in the Indigestible, polysaccharide exoskeletons serves as a β(1→4) glycosidic composed of N- of insects and source of dietary bonds between N- acetylglucosamine fungal cell fiber. acetylglucosamine units linked by β(1→4) bonds. walls. units. Inulin A storage Found in Indigestible by polysaccharide plants, (e.g., human enzymes composed of fructose garlic, onion). but ferments in β(2→1) glycosidic units linked by β(2→1) bonds. the gut, bonds between promoting fructose units beneficial gut bacteria. Formative Questions Formative Questions  Definition: Mucopolysaccharides, or glycosaminoglycans (GAGs), are long, unbranched polysaccharides composed of repeating disaccharide units. Each disaccharide unit typically contains: Mucopolysaccharides An amino sugar (such as N- acetylglucosamine or N- (Glycosaminoglycans, acetylgalactosamine). GAGs) A uronic acid (such as glucuronic acid or iduronic acid).  General Characteristics: Negatively Charged: Due to sulfate and carboxyl groups, GAGs are highly negatively charged, which attracts water molecules. Mucopolysaccharides Hydrophilic: Their structure (Glycosaminoglycans, allows them to form gel-like substances that retain water, GAGs) making them ideal for lubricating and cushioning tissues. Location: Found in connective tissues, cartilage, skin, blood vessels, and the extracellular matrix (ECM).  Major Types: Hyaluronic Acid Chondroitin Sulfate 2. Types of GAGs Dermatan Sulfate Heparan Sulfate Keratan Sulfate Heparin A. Hyaluronic Acid A. Hyaluronic Acid  Structure: Composed of repeating disaccharide units containing glucosamine and iduronic acid or glucuronic acid. B. Heparin Highly Sulfated: Heparin has a high degree of sulfation. Found primarily in mast cells within the lungs, liver, and lining of blood vessels..  Functions: Anticoagulation: Prevents blood clot formation by activating antithrombin III, a protein that inhibits thrombin. Clinical Importance: Anticoagulant Therapy: B. Heparin Treatment of Thromboembolic Disorders: Heparin is essential in managing heart attacks, strokes, and pulmonary embolisms. Safe Use in Pregnancy: Heparin is often preferred for pregnant women as it does not cross the placenta, unlike some other anticoagulants.  1.Hyaluronic acid is unique among glycosaminoglycans (GAGs) because it is: A) Highly sulfated B) Partially sulfated C) Non-sulfated D) Only sulfated in specific tissues Formative 2. Which two repeating disaccharide units make up hyaluronic acid? Questions A) N-acetylglucosamine and glucuronic acid B) Glucose and galactose C) N-acetylgalactosamine and iduronic acid D) Fructose and mannose  3.What is the primary medical use of heparin? Formative A) To promote skin hydration B) To provide joint lubrication Questions C) To prevent blood clotting D) To support bone growth References Lippincott Illustrated Reviews: Biochemistry Eighth Edition Thank You