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Biochemistry 1 (MLBC-201)

Biochemistry 1 (MLBC-201). Dr. Hewida Fadel Dr. Tarek El Sewedy. Lecture 3 Carbohydrates Structure And classification. Intended Learning Outcomes. By the end of this lecture, students will learn: The basic structure and classes of carbohydrates . Lecture content.

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Biochemistry 1 (MLBC-201)

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  1. Biochemistry 1(MLBC-201) • Dr. HewidaFadel • Dr. Tarek El Sewedy

  2. Lecture 3 Carbohydrates Structure And classification

  3. Intended Learning Outcomes By the end of this lecture, students will learn: The basic structure and classes of carbohydrates.

  4. Lecture content • What are carbohydrates? • Classification of carbohydrates. • Classification of monosaccharides. • Reducing & non reducing sugars. • Classification of polysaccharides.

  5. Biomolecules of life • Carbohydrates • Proteins. • Lipids • Nucleic acids

  6. What are carbohydrates? • In biochemistry, carbohydrates is a synonymous of saccharide. •  The word saccharidecomes from the Greekwordsákkharon, meaning “sugar". • The term carbohydrate often means any food that is particularly rich in the comples carbohydratestarch (such as cereals, bread, and pasta) or simple carbohydrates, such as sugar (found in candy, jams, and desserts). • Carbo-hydrate is composed of carbon and water (C.H2O)n. For every carbon there is 1 water molecule or 2 hydrogen atoms and 1 oxygen atom (with some exceptions).

  7. Classification of carbohydrates There are a variety of classification schemes. • The most common classification scheme divides the carbohydrates into groups according to the number of individual simple sugar units. • Monosaccharides contain a single unit • disaccharides contain two sugar units (2 monosaccharides) • polysaccharides contain many sugar units as in polymers

  8. Monosaccharides can be further classified by the number of carbons present. • Six carbons = Hexose (ex. Glucose, Galactose,fructose) • Five carbons = Pentose (ex. Ribose) • Four = Tetrose (Erythose) • Three = Triose (Glyceraldehyde)

  9. Modified monosaccharides • phosphorylated sugars are one example of modified monosaccharides. • An important phosphorylated sugar is glucose 6-phosphate. • glucose 6-phosphate provides energy in certain metabolic pathways, and it can be converted and stored as glycogen when blood glucose levels are high. If blood glucose levels are low, glucose 6-phosphate can be converted back into glucose to enter the bloodstream again. • glucose 6-phosphate possesses a negative charge. This prevents the molecule from leaving the lipid-bilayer membranes. This allows the cell to easily uses the modified sugar to provide energy, or convert it to glycogen as storage.

  10. Classification according to Functional Groups • Aldoses: Are sugars containing an aldehyde functional group on carbon #1 (anomeric carbon)- Monosaccharides in this group are glucose, galactose, ribose, and glyceraldehyde. • Ketoses: Sugars containing the ketone group on carbon # 2 (anomeric carbon)- The major sugar in this group is fructose.

  11. Classification according to reducing capability • Reducing capability is defined by the presence of free aldehyde or ketone group. • A. Reducing: Contain free groups (contain one free anomeric carbon atom), glucose, maltose, lactose and fructose. • All Monosaccharides are reducing sugars. Two of three disaccharides maltose and lactose, have the free groups needed to act as reducing agents.  • B. Non-reducing: Contain no free groups. • Sucrose and polysaccharides are non reducing. • (sucrose's anomeric carbon is not "free" since this carbon is used to link fructose and glucose together.

  12. Reducing Disaccharides Maltose Lactose

  13. Non reducing disaccharide

  14. Classification of polysaccharides • Homo-polysaccharides (all the same type) • Hetero-polysaccharides (mixtures of monomer types) • Complex carbohydrates (joined to non-carbohydrate molecules)

  15. 1-Monosaccharides (CH20)n 3. Polysaccharides 2-Disaccharides

  16. Disaccharides fructose glucose galactosea monosaccharaides… joined together to make disaccharides. sucrose maltose lactose (fructose-glucose) (glucose-glucose) (glucose-galactose)

  17. Glucose Polysaccharides Cellulose Glycogen Starch (unbranched) Starch (branched)

  18. ASSIGNMENTS Students selected in the previous slide are requested to prepare slides about any of the following topics and delivered before next lecture: • Importance of carbohydrates in human life. • Carbohydrates and cell membrane. • Carbohydrates in plants. • Importance of glycogen. • Disease related to high glucose level. • Disease related to low glucose level. • Polysaccharides. • Functions of glycoprotein. • Carbohydrate and energy. • Carbohydrate digestion.

  19. Students selected for assignment

  20. Study Questions: • Mention the 4 major biomolecules of life. • Mention one classification of carbohydrates giving examples. • Explain why sucrose is a non reducing while maltose is a reducing sugar

  21. Suggested readings: • Harper’s Biochemistry 26th edition

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