RVHS 4. Lipids

River Valley High School 1 2025 JC1 H2 Biology Lecture Topic 4: Biomolecules of Life - Lipids River Valley High School 2025 JC1 H2 Biology Lecture Topic 4: Biomolecules of Life - Lipids Name: ( ) Class: 25J__ Date: References Title Authors Biology (9th Edition) Campbell and Reece Longman A-Level Course in Biology: Core Syllabus Volume 1 Hoh Biological Science 1. Organisms, Energy and Environment (3rd Edition) Taylor, Green, Stout and Soper Understanding Biology for Advanced Level (4th Edition) Toole and Toole H2 Biology Syllabus 9477 (2025) Candidates should be able to use the knowledge gained in the following section(s) in new situations or to solve related problems. Related Topics Concepts Biomolecules of Life and Cellular Transport The structure of carbohydrates, lipids and proteins and their roles in living organisms Transformation of Energy between the Environment and Organisms The need for energy in living organisms Learning Outcomes 1B. Biomolecules of Life and Cellular Transport g. Describe the structure and properties of the following monomers: i. α-glucose and β-glucose (in carbohydrates) ii. glycerol and fatty acids (in lipids) iii. amino acids (in proteins) (chemical formulae of specific R-groups of different amino acids are not required) h. Describe the formation and breakage of the following bonds: i. glycosidic bond ii. ester bond iii. peptide bond i. Describe the structures and properties of the following biomolecules and explain how these are related to their roles in living organisms: i. starch (including amylose and amylopectin) ii. cellulose iii. glycogen iv. triglyceride v. phospholipid For practical, candidates should be able to: • carry out the emulsion test for lipids.

River Valley High School 2 2025 JC1 H2 Biology Lecture Topic 4: Biomolecules of Life - Lipids Lecture Outline I. Importance of Lipids II. Nature of Lipids III. Fats IV. Phospholipids V. Glycolipid VI. Cholesterol I. Importance of Lipids Lipids are a heterogonous group of compounds inclusive of fats, oils, waxes, steroids and phospholipids. In general, l ipids perform three biological functions (although certain lipids apparently serve more than one purpose in some cells): 1. Lipids containing hydrocarbon chains serve as energy stores. 2. Lipid molecules in the form of lipid bilayers are essential components of biological m embranes. 3. Many intra- and intercellular signaling events involve lipid molecules. II. Nature of Lipids • Lipids are a group of organic compounds whose molecules contain atoms of carbon, hydrogen, and oxygen only. • General formula: No general formula but t he ratio of hydrogen atoms to oxygen atoms is always much greater than 2:1. For example, tristearin: C57H110O6. • Structure-Property Relationship: o Although lipids are not polymers, they are large molecules assembled from smaller molecules by condensation reactions. Most lipids are esters of an alcohol and fatty acids. o Lipids comprise of two components: 1. Glycerol  Glycerol is an alcohol.  It has 3 hydroxyl groups: each hydroxyl group may be used to form an ester bond with a separate fatty acid, forming a triglyceride. 2. Fatty acids A fatty acid consists of a hydrocarbon chain and a carboxyl group. Its general formula is RCOOH, where R is the hydrocarbon chain.  A hydrocarbon chain consists of a chain of carbon atoms to which hydrogen atoms are attached.  Fatty acids may be saturated or unsaturated.  The hydrocarbon tail is hydrophobic and causes lipids to be insoluble in water.  The effect o f the non-polar hydrocarbon chain is enough to overcome the polarity of the carboxyl group, so most fatty acids have low solubility in water.

River Valley High School 3 2025 JC1 H2 Biology Lecture Topic 4: Biomolecules of Life - Lipids  The length of the hydrocarbon chain differs from one fatty acid to another. Those most frequently found in living organisms have 15-17 carbon atoms. o Lipids are insoluble in water but are soluble in organic solvents such as ethanol, ether and trichloromethane (chloroform). SATURATED FATTY ACIDS • In saturated fatty acids, each carbon atom in the chain is joined to the next by single covalent bonds (i.e. does not contain carbon -carbon double bonds ) – it thus has the maximum possible number of hydrogen atoms. • E.g. palmitic acid and stearic acid. Source: Longman A-Level Course in Biology: Core Syllabus Volume 1. pp.60 UNSATURATED FATTY ACIDS • The hydrocarbon chain of unsaturated fatty acids has one or more double covalent bonds (i.e. contains carbon-carbon double bond(s)). • Pronounced kinks (bends) occur in the hydrocarbon chain where double bonds exist. • The kinks prevent the molecules from packing together closely enough to solidify at room temperatures. • E.g. Oleic acid. Geometric isomerism occurs in unsaturated fatty acids. If the hydrocarbon chains are on the same side of the double bond, it is a cis fatty acid. E.g. Oleic acid has 18 carbon atoms and contains one carbon-carbon double bond. Naturally occurring unsatur ated fatty acids are nearly all of the cis configuration, leading to kinks in the structure.

River Valley High School 4 2025 JC1 H2 Biology Lecture Topic 4: Biomolecules of Life - Lipids • Classification of Lipids: Simple Lipids Complex Lipids Steroids and Sterols Are esters of fatty acids with various alcohols Consist of both lipid and non - lipid components Consists of four rings of carbon atoms interconnected to form the main skeleton, with side chains of variable length. Examples: 1. Fats are esters of fatty acids with glycerol. Oils are fats in the liquid state. E.g. monog lycerides, diglycerides, and triglycerides. 2. Waxes are esters of fatty acids with high molecular weight alcohols . E.g. waxes found in the cuticle of leaves and exoskeleton of insects Examples: 1. Phospholipids contain a phosphate group (i.e. the non-lipid component) in addition to fatty acids and glycerol. 2. Glycolipids contain a carbohydrate group as the non-lipid component. Example: 1. Cholesterol is an important cell membrane component and a precursor of all other steroids. III. Fats • Fats are the simplest and commonest lipid molecules in nature. • They are large molecules but are NOT polymers. • Structure: o The components of fats are fatty acids and glycerol. o Examples of fats - monoglyceride, diglyceride and trigly ceride and the reactions for their formation are represented by the following equations: 1 Fatty acid + Glycerol → Monoglyceride + Water 2 Fatty acids + Glycerol → Diglyceride + 2 Water 3 Fatty acids + Glycerol → Triglyceride + 3 Water • Synthesis of a triglyceride: o 3 fatty acid molecules combine with 1 glycerol molecule. o each hydroxyl group (-OH) in the glycerol molecule reacts with the carboxyl group of a fatty acid. o in this reaction, an ester bond is formed between the glycerol and fatty acid, with the removal of a molecule of water – this is a condensation reaction. o since glycerol has 3 hydroxyl groups, 3 fatty acids attach themselves to the glycerol molecule and hence, 3 molecules of water are removed.

River Valley High School 5 2025 JC1 H2 Biology Lecture Topic 4: Biomolecules of Life - Lipids Source: Longman A-Level Course in Biology: Core Syllabus Volume 1. pp.61 • Relating structure to function: 1. As a storage form of energy Structure-Property Significance S: Triglyceride molecules are large and uncharged P: This makes them insoluble in water Being insoluble, they can be stored in large amounts without having any great effect on the water potential of the cells. They are also prevented from leaving the cells. S: Triglyceride molecules