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Nutrients (part 1): Carbohydrates

Lesson objectives<br>- list the chemical elements which make up<br>u2022 carbohydrates

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Nutrients (part 1): Carbohydrates

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  1. Nutrients Nutrients Nutrients Chapter 4 Chapter 4

  2. Lesson objectives: • Introduction to the need for food and the 7 classes of food • Carbohydrates (monosaccharides, disaccharides and polysaccharides) • New terms: condensation, polymerisation & hydrolysis • Structure and function of starch, glycogen and cellulose • Fats – structure and function

  3. Need for food 1. To provide energy for vital activities of body 2. To synthesize new protoplasm (for growth, repair, reproduction) 3. To maintain health (prevent deficiency diseases) 4. Movement (locomotion)

  4. 7 classes of food 7 classes of food 7 classes of food

  5. Activity: In pairs, identify the various ingredients and nutrients present in a burger

  6. Ingredients Nutrients present Carbohydrate, vitamins, fibre Bread Carbohydrate, protein, vitamins, fibre, minerals, water Carbohydrate, protein, vitamins, fibre, minerals, water Proteins, fats, minerals Lettuce Tomato Beef Cheese Fats, proteins, vitamins, minerals (Ca2+)

  7. Nutrients in food (7 classes of food) • Carbohydrates • Proteins • Fats • Vitamins • Dietary fibre Organic nutrients (obtained from living organisms; compounds of carbon) • Water • Mineral salts Inorganic nutrients

  8. Question: • Which class of food provides the most energy to the body? • Why is it than not advisable for people who want to lose weight to consume more carbohydrates in place of proteins or fats?

  9. Carbohydrates Carbohydrates Carbohydrates

  10. Carbohydrate Carbohydrates Monosaccharides (simple sugars) Disaccharides (complex sugars) Polysaccharides starch cellulose glycogen glucose, galactose, fructose e.g. maltose, lactose, sucrose

  11. Carbohydrates • Generalised formula: CnH2mOm • e.g. glucose n = 6, m = 6 formula: C6H12O6 sucrose n = 12, m = 11 formula: C12H22O11

  12. Types of sugar Monosaccharides Disaccharides condensation condensation condensation

  13. Condensation • is a chemical reaction whereby 2 simple molecules are joined together to form a larger molecule with the removal of one molecule of water

  14. Polymerisation Definition: • process of condensing many similar molecules to form a large molecule glucose

  15. Hydrolysis • A reaction whereby a water molecule is added to split up a complex molecule into its constituent units 1. 2.

  16. *Disaccharides & Monosaccharides Disaccharide Monosaccharide maltase maltose glucose + glucose lactase lactose glucose + galactose sucrase sucrose glucose + fructose

  17. Summary: Carbohydrates Monosaccharides (simple sugars) Disaccharides (complex sugars) Polysaccharides condensation starch cellulose glycogen glucose, galactose, fructose e.g. maltose, lactose, sucrose hydrolysis polymerisation

  18. Starch Starch Glycogen Glycogen Starch Glycogen Cellulose Cellulose Cellulose

  19. Starch • Most impt. source of carbohydrates in our food • Rich in vegetable foods (cereals, potatoes) • Not formed or stored by animals • Detected by iodine test

  20. Starch Mixture of straight & branched chains linked by chemical bonds Hydrolysis by acids/enzymes break bonds → releasing reducing sugars

  21. Glycogen • a.k.a “animal starch” • Formed when numerous glucose units condense to form highly branched chains of glucose units • Storage form of carbohydrate in animals & fungi • Animals: stored mainly in liver & muscles

  22. Starch & Glycogen are suitable storage materials because… 1. Insoluble in H2O (do not change osmotic pressure in cells) 2. Large molecules (unable to diffuse through cell membrane) 3. Can easily be hydrolysed to glucose when needed 4. Molecules have compact shape (occupy less space c.f. glucose molecules)

  23. Using mneumonics • In pairs, use mneumonics to memorise the points on why starch & glycogen are suitable as storage materials L arge molecule I nsoluble C ompact shape E asily hydrolysed

  24. Cellulose • Carbohydrate that forms greater part of cell walls of plants • Similar to starch (consists of glucose units linked together to form straight chains) • Differ in the way glucose units are linked between them • Inert (digestible by few organisms) → forms bulk of undigested matter in Man • Fibre important to proper functioning of large intestine

  25. Functions of carbohydrates • As source of energy • To form supporting structures e.g. cellulose cell walls • *Converted to other organic compounds e.g. amino acids and fats • Formation of nucleic acids (DNA) • To synthesize lubricants (mucus → carbohydrate + protein)

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