Carbohydrates Lecture Notes PDF

SCHOOL OF MEDICINE & HEALTH SCIENCES LECTURE 3. BIOMOLECULES PMBI 130 3.1 CARBOHYDRATES Lecturer: Mr. Musona Motivational Corner Philippians 3: 13 - 14 The Word of God in Philippians 3:13-14 inspires students to let go of...

SCHOOL OF MEDICINE & HEALTH SCIENCES LECTURE 3. BIOMOLECULES PMBI 130 3.1 CARBOHYDRATES Lecturer: Mr. Musona Motivational Corner Philippians 3: 13 - 14 The Word of God in Philippians 3:13-14 inspires students to let go of past struggles and focus on the future. Students are encouraged to embrace challenges with positivity, continually strive for excellence, and remain dedicated to their goals. The journey in medicine is a relentless pursuit of knowledge and compassion, for the betterment of Mankind. Never give up on this noble call. Other Motivational Quotes:- 2. The man who moves a mountain begins by carrying away small stones (Aristotle, Ancient Wisdom) 3. The future belongs to those who believe in the beauty of Loading… their dreams (Lao Tzu, Ancient Wisdom)  All wrong-doing is sin, 1 John 5:17 Tell Your The Joy of Medicine Story Loading…  SCOPE: 1. Structure 2. Function 3. metabolism  DEFINITION AND DESCRIPTION OF CARBOHYDRATES: Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically in the ratio (CH₂O)ₙ, where n is the number of carbon atoms. They are essential biomolecules that serve as a primary energy source and structural components in living organisms.  SOURCES OF CARBOHYDRATES: Plants: Grains, fruits, vegetables, legumes. Animals: Glycogen in the liver and muscles. Dairy Products: Lactose in milk.  GENERAL STRUCTURE OF CARBOHYDRATES: Carbohydrates are classified based on the number of carbon atoms and complexity: Monosaccharides: Single sugar units (e.g., glucose, fructose, galactose). Disaccharides: Two monosaccharides linked by a glycosidic bond (e.g., sucrose, lactose, maltose). Polysaccharides: Long chains of monosaccharide units (e.g., starch, glycogen, cellulose). 2 Design Structures of Glucose Loading…  CLASSIFICATION BY CARBON ATOMS: Triose: 3 carbons (e.g., glyceraldehyde) Tetrose: 4 carbons (e.g., erythrose) Pentose: 5 carbons (e.g., ribose, xylose) Hexose: 6 carbons (e.g., glucose, fructose, galactose) Heptose: 7 carbons (e.g., sedoheptulose) Octose: 8 carbons (rare)  PHYSICAL PROPERTIES OF CARBOHYDRATES: Solubility: Monosaccharides and disaccharides are generally soluble in water. Taste: Monosaccharides and some disaccharides are sweet. Crystallinity: Many sugars form crystals. Optical Activity: Carbohydrates can rotate plane-polarized light due to chiral centers.  CHEMICAL PROPERTIES OF CARBOHYDRATES: Synthesis and Hydrolysis: Disaccharides: Sucrose: Glucose + Fructose → Sucrose + Water Maltose: Glucose + Glucose → Maltose + Water Lactose: Glucose + Galactose → Lactose + Water Hydrolysis involves breaking the glycosidic bond using water and enzymes like sucrase, maltase, and lactase.  Dehydration Synthesis Reaction Two alpha-glucose units form a glycosidic linkage with elimination of water molecules to form one maltose molecule. So we can say that a dehydration synthesis always involves two steps. 1.Formation of a new product 2.Loss of water molecule Hydrolysis Reaction of Carbohydrates  Polysaccharides: Amylose: Linear chains of glucose units. Amylopectin: Branched chains of glucose units. Cellulose: Linear chains of β-glucose units. Glycogen: Highly branched chains of glucose units. Hydrolysis involves breaking down into monosaccharides by enzymes like amylase.  Reaction with Benedict's Solution: Reducing sugars (e.g., glucose, maltose) reduce copper(II) ions in Benedict's solution, forming a red precipitate of copper(I) oxide.  FUNCTIONS OF CARBOHYDRATES: 1. Energy Source: Primary source of energy for cells. 2. Energy Storage: Glycogen in animals and starch in plants. 3. Structural Role: Cellulose in plant cell walls and chitin in fungi. 4. Cell Recognition: Glycoproteins and glycolipids on cell membranes. 5. Metabolic Intermediates: Involved in metabolic pathways like glycolysis.  BRANCHED AND UNBRANCHED CARBOHYDRATES: Unbranched: Linear chains of monosaccharides (e.g., amylose, cellulose). Branched: Chains with side branches (e.g., amylopectin, glycogen). Reaction of Simple Sugars with Benedict’s Solution  FATE OF CARBOHYDRATES IN PLANTS: Storage: Stored as starch (amylose and amylopectin). Utilization: Glucose used in cellular respiration for energy.  FATE OF CARBOHYDRATES IN ANIMALS: Blood Sugar Regulation: Insulin: Lowers blood glucose by promoting its uptake into cells and storage as glycogen in the liver and muscles. Glucagon: Raises blood glucose by promoting glycogen breakdown and gluconeogenesis.  Pancreas: Secretes insulin and glucagon. Liver: Central role in glycogen storage and glucose regulation. Diabetes: Type 1 (insulin deficiency), Type 2 (insulin resistance). Blood Sugar Regulation  METABOLIC PATHWAYS: Gluconeogenesis: Synthesis of glucose from non- carbohydrate sources. Loading… Glycolysis: Breakdown of glucose to pyruvate, yielding ATP. Glycogenesis: Formation of glycogen from glucose. Ketoacidosis: Accumulation of ketones due to excessive fat breakdown, often seen in uncontrolled diabetes.  REDUCING SUGARS: Reducing sugars are carbohydrates that can act as reducing agents because they have a free aldehyde group (-CHO) or a free ketone group (-C=O) that can be oxidized. In other words, these sugars can donate electrons to other molecules, such as copper(II) ions in Benedict's solution, resulting in a reduction reaction.  Examples of Reducing Sugars: 1. Glucose 2. Fructose 3. Galactose 4. Maltose 5. Lactose  Why These Sugars React with Benedict's Solution? Benedict's Solution is a chemical reagent used to detect the presence of reducing sugars. It contains copper(II) sulfate (CuSO₄), sodium carbonate (Na₂CO₃), and sodium citrate. When heated with a reducing sugar, the solution undergoes a redox reaction where the copper(II) ions (Cu²⁺) are reduced to copper(I) ions (Cu⁺), forming a precipitate of copper(I) oxide (Cu₂O), which is red or orange.  Glucose and Galactose: These are aldoses, containing a free aldehyde group that can be easily oxidized. Fructose: Although a ketose, it can isomerize under basic conditions to form an aldose, which then reacts as a reducing sugar. Maltose and Lactose: These disaccharides have a free aldehyde group at the anomeric carbon of one of their monosaccharide units, allowing them to act as reducing agents.  Reaction Mechanism with Benedict's Solution 1. Preparation: Mix the carbohydrate solution with Benedict's solution. 2. Heating: Heat the mixture in a boiling water bath. 3. Observation: If reducing sugars are present, the solution changes color: Blue (no reducing sugar) Green to yellow (low concentration of reducing sugar) Orange to red (high concentration of reducing sugar)  This color change indicates the reduction of copper(II) sulfate (blue) to copper(I) oxide (red/orange), confirming the presence of reducing sugars.  Concepts of Triose, Tetrose, Pentose, Hexose, and Dextrose Sugars 1. Triose Sugars Definition: Triose sugars are monosaccharides with three carbon atoms. Examples: Glyceraldehyde: An aldose with the chemical formula C₃H₆O₃. It has a single aldehyde group. Dihydroxyacetone: A ketose with the same chemical formula but with a ketone group instead of an aldehyde.  2. Tetrose Sugars Definition: Tetrose sugars are monosaccharides with four carbon atoms. Examples: Erythrose: An aldose with the chemical formula C₄H₈O₄, containing an aldehyde group. Erythrulose: A ketose with the same formula, containing a ketone group.  3. Pentose Sugars Definition: Pentose sugars are monosaccharides with five carbon atoms. Examples: Ribose: An aldose with the chemical formula C₅H₁₀O₅, found in RNA. Ribulose: A ketose with the chemical formula C₅H₁₀O₅, involved in the Calvin cycle of photosynthesis.  4. Hexose Sugars Definition: Hexose sugars are monosaccharides with six carbon atoms. Examples: Glucose: An aldose with the chemical formula C₆H₁₂O₆, a primary energy source in cells. Fructose: A ketose with the same formula, commonly found in fruits.  Dextrose: Definition: Dextrose is another name for D-glucose, specifically referring to the dextrorotatory form of glucose. It is called "dextrose" because it rotates plane-polarized light to the right. Example: Dextrose: D-glucose, an important sugar in human metabolism. Summary Table of Examples: Type of Sugar Definition Examples Glyceraldehyde, Triose 3 carbon atoms Dihydroxyacetone Tetrose 4 carbon atoms Erythrose, Erythrulose Pentose 5 carbon atoms Ribose, Ribulose Hexose 6 carbon atoms Glucose, Fructose D-glucose, specifically the Dextrose Dextrose (D-glucose) dextrorotatory form  These sugars play various roles in biological processes, from energy metabolism to structural components in nucleic acids and other cellular functions.  Sweetness of Sugars: Comparative Analysis: The perception of sweetness varies among different sugars. Fructose is generally considered the sweetest naturally occurring monosaccharide. Here's a comparison of the sweetness levels of various sugars and honey:  Comparative Sweetness of Different Sugars 1. Fructose Sweetness Index: 1.7 (Relative to Sucrose = 1) Characteristics: The sweetest natural sugar, commonly found in fruits, honey, and root vegetables. Its high sweetness is due to its ability to fit well into sweet taste receptors on the tongue.  2. Sucrose (Table Sugar) Sweetness Index: 1.0 Characteristics: Standard reference for sweetness. It is a disaccharide composed of glucose and fructose, commonly used as a sweetener in many foods.  3. Glucose (Dextrose) o Sweetness Index: 0.7 o Characteristics: Less sweet than sucrose, found in fruits, vegetables, and honey. It is a primary energy source for the body.  3. Honey o Sweetness Index: ~1.3-1.5 (varies depending on floral source) o Characteristics: Contains fructose, glucose, sucrose, and other sugars. Its sweetness comes primarily from fructose and glucose.  4. Galactose Sweetness Index: 0.6 Characteristics: Less sweet than glucose and sucrose. Found in milk as part of lactose (a disaccharide).  5. Maltose Sweetness Index: 0.4 Characteristics: A disaccharide composed of two glucose molecules. Found in malt and used in brewing and baking.  6. Lactose (Milk Sugar) Sweetness Index: 0.2 Characteristics: The least sweet among the common sugars, found in milk. It is a disaccharide composed of glucose and galactose.  7. High Fructose Corn Syrup (HFCS) Sweetness Index: ~1.0-1.2 (varies by formulation) Characteristics: A mixture of glucose and fructose. Used extensively in processed foods and beverages.  Summary Table of Sweetness Comparison Sugar Type Sweetness Index Characteristics Sweetest natural Fructose Monosaccharide 1.7 sugar, found in fruits and honey. Standard for Sucrose Disaccharide 1.0 sweetness, common table sugar. Less sweet than Glucose (Dextrose) Monosaccharide 0.7 sucrose, primary  energy source. Varies by floral source, high in Honey Natural Mix 1.3-1.5 fructose and glucose. Found in milk as part Galactose Monosaccharide 0.6 of lactose. Found in malt, used Maltose Disaccharide 0.4 in brewing and baking. Least sweet, found in Lactose Disaccharide 0.2 milk.  Factors Affecting Sweetness Perception: Chemical Structure: The arrangement of atoms in the sugar molecule affects how it interacts with taste receptors. Concentration: Higher concentrations can enhance perceived sweetness. Temperature: Sweetness perception can change with temperature; some sugars taste sweeter at different temperatures. Presence of Other Substances: The presence of acids, salts, or other compounds can alter the perception of sweetness.  Fructose's high sweetness is due to its structural compatibility with sweet taste receptors, making it the sweetest among commonly consumed sugars.  Glycosidic Bonds in Carbohydrates: Common Glycosidic Bonds 1,4-Glycosidic Linkage Definition: A bond formed between the hydroxyl group on the first carbon (C1) of one monosaccharide and the hydroxyl group on the fourth carbon (C4) of another monosaccharide.  Where Found: Starch: Amylose (linear chains) and amylopectin (branched chains). Glycogen: Branched polysaccharide in animals. Maltose: Disaccharide of two glucose units.  Structure: Alpha (α) 1,4-glycosidic bond: Found in amylose and the linear sections of amylopectin and glycogen. Beta (β) 1,4-glycosidic bond: Found in cellulose, where it forms straight, rigid chains due to the β configuration.  1,6-Glycosidic Linkage Definition: A bond formed between the hydroxyl group on the first carbon (C1) of one monosaccharide and the hydroxyl group on the sixth carbon (C6) of another monosaccharide.  Where Found: Amylopectin: Branched component of starch. Glycogen: Highly branched polysaccharide in animals. Isomaltose: Disaccharide of two glucose units linked by an α-1,6 bond. Structure: Creates branches in polysaccharides, contributing to their compact and energy-dense structure.  Synthesis and Hydrolysis of Glycosidic Bonds 1. Synthesis (Condensation Reaction) o Process: Enzymatic Catalysis: Enzymes such as glycosyltransferases facilitate the formation of glycosidic bonds. C6H12O6+C6H12O6→C12H22O11+H2O  Water Release: A molecule of water (H₂O) is released during the reaction. The hydroxyl group (-OH) from one monosaccharide reacts with the hydrogen (H) from the hydroxyl group of another monosaccharide.  2. Hydrolysis (Decomposition Reaction) Process: Enzymatic Catalysis: Enzymes such as amylase, maltase, lactase, and sucrase catalyze the hydrolysis of glycosidic bonds. Water Addition: A molecule of water (H₂O) is added to break the glycosidic bond, yielding two monosaccharides.  Example: Hydrolysis of Maltose: Maltase enzyme catalyzes the breakdown of maltose into two glucose molecules using water. C12H22O11+H2O→C6H12O6+C6H12O6  Summary: 1,4-Glycosidic Linkage: Found in linear polysaccharides like amylose and cellulose (β configuration) and in the linear portions of amylopectin and glycogen (α configuration). 1,6-Glycosidic Linkage: Found at the branch points in polysaccharides like amylopectin and glycogen. Synthesis: Involves the removal of water and the formation of glycosidic bonds catalyzed by enzymes. Hydrolysis: Involves the addition of water to break glycosidic bonds, also catalyzed by specific enzymes.  Blood glucose regulation: Regulation of glucose in the body is done autonomically and constantly throughout each minute of the day. Normal BG levels should be between 60 and 140 mg/dL in order to supply cells of the body with its required energy. Brain cells don’t require insulin to drive glucose into neurons; however, there must still be normal amounts available.  VIDEO ON CARBOHYDRATES https://www.youtube.com/watch?v=LeOUIXbFyqk&t=6s  Too little glucose, called hypoglycemia, starves cells, and too much glucose (hyperglycemia) creates a sticky, paralyzing effect on cells. Euglycemia, or blood sugar within the normal range, is naturally ideal for the body’s functions. A delicate balance between hormones of the pancreas, intestines, brain, and even adrenals is required to maintain normal BG levels. Bibliography/References: Anderson, D.M., Novak, P.D., Keith, J. and Elliot, M.A. (2003). Dorlands’s Illustrated Medical Dictionary. 30th Edition. Saundeers. Clegg, C.J. and Mackean, D.G. (2008). Advanced Biology: Principles and Applications, Second Edition. Hodder Education. London. https://www.istockphoto.com. Raven, P.H., Johnson, G.B., Mason, K.A., Losos, J.B. and Singer, S.R. (2014). Biology, 10th Edition. McGraw-Hill Co. Sastry, A.S. and Bhat, S. (2019). Essentials of Medical Microbiology. Jaypee Brothers Medical Publishers. New Delhi. Soper, R., Taylor, D.J., Green, N.P.O. and Stout, G.W. (2017). Biological Science 1 & 2. Cambridge University Press.  THE END Any Questions??? Thank You for Your Attention!