RVHS 3. Carbohydrates

River Valley High School 1 2025 JC1 H2 Biology Lecture Topic 3: Biomolecules of Life - Carbohydrates River Valley High School 2025 JC1 H2 Biology Lecture Topic 3: Biomolecules of Life - Carbohydrates Name: ( ) Class: 25J__ Date: References Title Authors Biology (9th Edition) Campbell and Reece Biological Science 1. Organisms, Energy and Environment (3rd Edition) Taylor, Green, Stout and Soper Longman A-Level Course in Biology: Core Syllabus Vol. 1 Hoh Understanding Biology for Advanced Level (4th Edition) G. Toole and S. 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 Synthesis of carbohydrates from carbon dioxide and water during photosynthesis 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 tests for reducing and non -reducing sugars using acid hydrolysis and Benedict’s solution (including quantitative use of the Benedict’s test) and the iodine in potassium iodide solution test for starch.

River Valley High School 2 2025 JC1 H2 Biology Lecture Topic 3: Biomolecules of Life - Carbohydrates Lecture Outline I. Biomolecules II. Importance of Carbohydrates III. Nature of Carbohydrates IV. Monosaccharides A. Aldose vs Ketose B. Linear vs Ring Structures C. Isomerism:  vs  Isomers V. Disaccharides VI. Polysaccharides A. Storage Polysaccharides – relating structure to function B. Structural Polysaccharides – relating structure to function I. Biomolecules • The enormous diversity of molecules in organisms fall into four main classes: 1. Carbohydrates 2. Lipids 3. Proteins 4. Nucleic acids • These molecules are involved in maintenance and metabolic processes of all living things, and are known as biological molecules. • Three of the four classes of biological molecules - carbohydrates, proteins and nucleic acids - are chain-like molecules called polymers. - A polymer is a long molecule consisting of many similar or identical building blocks linked by covalent bonds. - The repeating units that serve as the building blocks of a polymer are smaller molecules called monomers. • Large biological molecules exhibit unique properties arising from the orderly arrangement of their monomers and their functional groups. • The classes of polymers differ in the nature of their monomers, but the chemical mechanisms by which cells make and break down polymers are basically the same in all cases. In cells, these processes are facilitated by enzymes.

River Valley High School 3 2025 JC1 H2 Biology Lecture Topic 3: Biomolecules of Life - Carbohydrates SYNTHESIS OF POLYMER – CONDENSATION / DEHYDRATION REACTION • Two molecules are covalently bonded to each other through loss of a water molecule. • When a bond forms between two monomers, one monomer provides a hydroxyl group (−OH), while the other provides a hydrogen (−H). • This reaction is repeated as monomers are added to the chain one by one, making a polymer BREAKING DOWN OF POLYMER – HYDROLYSIS • Bonds between the monomers are broken by the addition of water; with a hydrogen from the water molecule attaching to one monomer, and the hydroxyl group from the water molecule attaching to the other monomer. II. IMPORTANCE OF CARBOHYDRATES • In plants, carbohydrates are manufactured from carbon dioxide and water by photosynthesis. • Plants uses carbohydrates as an energy source (as glucose), as a means of storing energy (as starch) and as supporting material in the form of their cell walls (as cellulose). • Animals consume carbohydrates as an important component of a balanced die t or synthesise carbohydrates from amino acids via gluconeogenesis. Glucose is the most important carbohydrate: - It is the major metabolic fuel of mammals (except ruminants) and a universal fuel of the foetus. - It is the precursor for synthesis of all the other carbohydrates in the body, including glycogen for storage; ribose and deoxyribose in nucleic acids; galactose in lactose of milk; in glycolipids; and in combination with protein in glycoprotein and proteoglycans.

River Valley High School 4 2025 JC1 H2 Biology Lecture Topic 3: Biomolecules of Life - Carbohydrates III. NATURE OF CARBOHYDRATES • Carbohydrates are a group of organic compounds whose molecules contain atoms of carbon, hydrogen, and oxygen only. The ratio of hydrogen atoms to oxygen atoms is always 2:1. • General formula for any carbohydrate molecule: Cx(H2O)y. • Note: There are a few carbohydrates do not conform to the formula (e.g. deoxyribose, C 5H10O4) • Structure – Property Relationship: - All carbohydrates are either aldehydes or ketones - All contain several hydroxyl groups. • Therefore, carbohydrate chemistry is determined by the functional groups.  hydroxyl groups are not highly reactive, but they readily form hydrogen bonds and contribute to making sugars soluble in aqueous solution.  carbonyl groups are easily oxidized and hence are powerful reducing agents. • Classification of carbohydrates: - monosaccharides - disaccharides - polysaccharides Source: Biological Science 1. Organisms, Energy and Environment. 3rd Edition. pp.83

River Valley High School 5 2025 JC1 H2 Biology Lecture Topic 3: Biomolecules of Life - Carbohydrates IV. Monosaccharides • Monosaccharides are the simplest types of carbohydrates. • All carbohydrates are composed of simple monomers known as monosaccharides, arranged in repetitive patterns. • General formula: (CH2O)n, since they have the same number of carbon atoms as oxygen atoms in the molecule. • Nomenclature: Depending on the number of carbon atoms, n in the molecule, we have: - Triose C3H6O3, n = 3 e.g. glyceraldehyde, dihydroxyacetone - pentose C5H10O5, n = 5 e.g. ribose, ribulose - hexose C6H12O6, n = 6 e.g. glucose, galactose, fructose Note: Most names for sugars end in –ose. • Property of monosaccharides: All monosaccharides are reducing sugars. A. Aldose vs Ketose Depending on the location of the carbonyl group (C=O), a sugar is either an aldose or a ketose. • Aldose (i.e. an aldehyde sugar) – carbonyl group is located at the end of the carbon skeleton. • Ketose (i.e. a ketone sugar) – carbonyl group is located between two carbon atoms. The presence of an aldehyde or ketone group allows all monosaccharides to exhibit reducing properties. Glucose is an aldose, i.e. the chain of six carbon atoms is numbered beginning at the carbon of the aldehyde group. Source: Biology. 8th Edition. pp. 70

River Valley High School 6 2025 JC1 H2 Biology Lecture Topic 3: Biomolecules of Life - Carbohydrates B. Linear vs Ring Forms A hexose such as glucose can exist in linear or ring forms. • In aqueous solution, most hexose exist as rings rather than linear molecules as the ring structure requires the le