BIO 203 — General Physiology: Lecture Note

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BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Course code: BIO 203 Course title: General Physiology Course credit load: 2 Units Series 1: Chemistry of Organic Compounds • Part 1.1: Carbohydrates o Sub Part 1.1.1: Structure and classification of carbohydrates o Sub Part 1.1.2: Properties of carbohydrates o Sub Part 1.1.3: Biological importance of carbohydrates • Part 1.2: Lipids o Sub Part 1.2.1: Structure and classification of lipids o Sub Part 1.2.2: Properties of lipids o Sub Part 1.2.3: Biological importance of lipids • Part 1.3: Proteins o Sub Part 1.3.1: Amino acids and protein structure o Sub Part 1.3.2: Properties of proteins o Sub Part 1.3.3: Biological importance of proteins • Part 1.4: Nucleic Acids o Sub Part 1.4.1: Structure of DNA and RNA o Sub Part 1.4.2: Properties of nucleic acids o Sub Part 1.4.3: Biological importance of nucleic acids

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Introduction Living organisms are built from and powered by a relatively small set of organic molecules: carbohydrates, lipids, proteins, and nucleic acids. These four classes of biological macromolecules carry out all the structural, energetic, catalytic, regulatory, and informational functions that together constitute life at the molecular level. Understanding their chemistry is therefore the essential foundation of physiological understanding. This opening Series examines the structure, classification, properties, and biological importance of each of the four major classes of organic compounds. This molecular-level knowledge underpins the enzyme biochemistry, nutritional physiology, membrane biology, and regulatory physiology examined in the remaining Series of this course. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1 describe the structure, classification, properties, and biological importance of carbohydrates, • SLO 1.2 describe the structure, classification, properties, and biological importance of lipids, • SLO 1.3 describe the structure of amino acids and proteins, and explain the biological importance of proteins, and • SLO 1.4 describe the structure, properties, and biological importance of nucleic acids. 1.1 Carbohydrates 1.1.1 Structure and classification of carbohydrates Carbohydrates are organic compounds composed of carbon, hydrogen, and oxygen, typically in a ratio approximating CH2O (hence the name carbohydrate, meaning hydrated carbon); they are

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS classified by the number of monomer sugar units present: monosaccharides (single sugar units, such as glucose, fructose, and galactose) are the simplest and most fundamental carbohydrates; disaccharides (two monosaccharides joined by a glycosidic bond, such as sucrose, maltose, and lactose) form by condensation reactions; and polysaccharides (many monosaccharide units linked together, such as starch, glycogen, and cellulose) form large, structurally complex molecules. Glucose (C6H12O6) is the central monosaccharide in biology, existing in ring form in solution and serving as the primary fuel for cellular respiration in virtually all living organisms; the way glucose units are joined together in polysaccharides (the type of glycosidic bond and the degree of branching) determines the physical properties and biological role of the resulting polysaccharide, explaining why starch and cellulose, both built from glucose, have very different digestibility and structural properties. Fill in the blank: Carbohydrates are classified into monosaccharides, disaccharides, and ________ based on the number of monomer sugar units present. 1.1.2 Properties of carbohydrates Monosaccharides and disaccharides are generally soluble in water (hydrophilic) due to their numerous hydroxyl groups forming hydrogen bonds with water molecules, and many are sweet-tasting; they are reactive molecules, reducing sugars (such as glucose, fructose, and maltose) capable of acting as reducing agents due to a free aldehyde or ketone group, a property exploited in the Benedict and Fehling tests used to detect reducing sugars in biological samples. Polysaccharides display quite different physical properties from simple sugars: they are generally insoluble or only sparingly soluble in water (particularly cellulose), tasteless, and not sweet; their physical properties (solubility, viscosity, and gelling behaviour) are determined by their monomer sequence, degree of polymerisation, and the type and degree of branching, making polysaccharides extremely versatile molecules with widely varying physical characters despite sharing a carbohydrate chemical identity.

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Fill in the blank: ________ sugars, such as glucose and maltose, can act as reducing agents due to a free aldehyde or ketone group, a property detected by the Benedict test. 1.1.3 Biological importance of carbohydrates Carbohydrates serve as the primary energy source in most living organisms: glucose is oxidised through cellular respiration to yield ATP (adenosine triphosphate), the universal cellular energy currency; starch (in plants) and glycogen (in animals and fungi) serve as energy storage polysaccharides that can be broken down to release glucose when energy demands rise; and the pentose sugars ribose and deoxyribose form essential structural components of RNA and DNA respectively. Structural roles of carbohydrates include cellulose (a principal structural component of plant cell walls, providing rigidity and strength), chitin (a structural polysaccharide forming the exoskeleton of arthropods and the cell wall of fungi), and various glycoproteins and glycolipids on cell surfaces that play important roles in cell recognition, immune response, and cell-cell signalling. Fill in the blank: ________ serves as the energy storage polysaccharide in animals and fungi, broken down to release glucose when energy demands rise.

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS Figure 1.1: Carbohydrate structure and classification Pilot questions 1.1 1. Name the three classes of carbohydrates and give one example of each. 2. Explain why starch and cellulose have different properties despite both being made of glucose. 3. Define a reducing sugar and name two examples. 4. Name two biological roles of polysaccharides. 5. State the biological importance of the pentose sugars ribose and deoxyribose. 1.2 Lipids 1.2.1 Structure and classification of lipids Lipids are a diverse group of organic compounds defined not by a common chemical structure but by a shared physical property: they are insoluble in water but soluble in non-polar organic

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS solvents such as ether, chloroform, and benzene; the major lipid classes are triglycerides (triacylglycerols, composed of one glycerol molecule esterified with three fatty acid chains, the main form of fat storage in animals and plants), phospholipids (similar to triglycerides but with one fatty acid replaced by a phosphate-containing group, essential components of cell membranes), and sterols (including cholesterol and steroid hormones, characterised by a distinctive four-ring carbon skeleton). Fatty acids, the component chains of triglycerides and phospholipids, are classified as saturated (all carbon-carbon bonds in the chain are single bonds, generally solid at room temperature, such as palmitic and stearic acid found in animal fats) or unsaturated (containing one or more carbon-carbon double bonds, generally liquid at room temperature, such as oleic acid in olive oil and the polyunsaturated fatty acids found in many plant and fish oils). Fill in the blank: Lipids are defined by their shared physical property of being insoluble in ________ but soluble in non-polar organic solvents. 1.2.2 Properties of lipids The hydrophobic (water-repelling) nature of lipids arises from their predominantly non-polar hydrocarbon chains, which cannot form hydrogen bonds with water and are therefore excluded from aqueous environments; triglycerides are entirely hydrophobic, making them ideal energy-dense storage molecules, while phospholipids are amphipathic (having both a hydrophilic phosphate head and hydrophobic fatty acid tails), a dual character that drives the spontaneous formation of the lipid bilayer structure of cell membranes. The degree of unsaturation (number and arrangement of double bonds) in fatty acid chains profoundly affects lipid physical properties: saturated fatty acids pack closely together, forming relatively solid, high-melting-point fats (such as butter and lard), while unsaturated fatty acids, with their kinked double-bond geometry, cannot pack as closely, producing lower-melting-point oils (such as vegetable and fish oils) that remain liquid at lower temperatures. Fill in the blank: Phospholipids are ________ , having both a hydrophilic phosphate head and hydrophobic fatty acid tails, driving the formation of lipid bilayer membranes.

BIO la-NET | ONLINE LEARNING VIDEO PLATFORM FOR POST-SECONDARY & HIGHER INSTITUTION STUDENTS 1.2.3 Biological importance of lipids Lipids serve as the most energy-dense biological fuel, storing approximately twice the caloric energy per gram compared to carbohydrates or proteins, making triglyceride fat reserves the principal long-term energy store in most animals; the insulating properties of subcutaneous fat also provide thermal insulation and cushioning of internal organs; and phospholipids form the fundamental structural component of all biological membranes, governing which substances can cross the membrane. Sterols have diverse and critical regulatory functions: cholesterol is an essential component of animal cell membranes (influencing membrane fluidity) and the precursor for the biosynthesis of steroid hormones (including sex hormones such as oestrogen and testosterone, and adrenal hormones such as cortisol); fat-soluble vitamins (A, D, E, and K) are lipid-derived or lipid-associated molecules with essential roles in vision, calcium metabolism, antioxidant defence, and blood clotting respectively. Fill in the blank: ________ is an essential component of animal cell membranes and the precursor for steroid

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