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Understanding Carbohydrates and Their Structural Variations in Biology

Delve into the realm of carbohydrates, from monosaccharides to polysaccharides, exploring their structural variations and functions in living organisms. Gain insights into the complex chemistry of carbohydrates and their roles in cellular components.

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Understanding Carbohydrates and Their Structural Variations in Biology

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  1. Structure/Function of Cell Components • Living things are made of: • Carbohydrates • Lipids • Proteins • Nucleic acids • CHNOPS • Carbon • Hydrogen • Nitrogen • Oxygen • Phosphorous • Sulphur

  2. Basic Chemistry Strong Bonds • Atoms make bonds • Ionic loss/gain of electrons • Covalent electrons are shared • Polar covalent – unequal sharing of the electrons • Makes the atoms have a partial charge (polarity) • Hydrogen bonds • Between a polar covalently bonded hydrogen atom (e.g. to N or O) and another polar covalently bonded atom e.g. oxygen in a carbonyl group. • Polar covalent bonds, only a partial charge so relatively weak • Van der waals forces • Induced polarity (e.g. in C-H bond) • Hydrophobic Interactions • Non-polar groups tend to cluster together (away from water) • Polar groups tend to move towards water Weak Bonds

  3. CARBOHYDRATES

  4. Carbohydrates • C, H, O • (CH2O)n • Monosaccharides - one monomer • Form rings in solution • Disaccharides - two monomers • Polysaccharides - many monomers • Monomers contain • 5 Carbon atoms - pentose • 6 carbon atoms - hexose

  5. Carbohydrates • Saccharides can exist in solution as linear molecules or rings. • They interconvert between the two forms, but at equilibrium, 99% will be ring

  6. Structural Variation in Carbohydrates • Special carbons • Carbon atoms 1-5 are chiral (optically active) i.e. OH and H groups on the C atoms can be ordered differently. • For C atoms 2-4 the arrangement of OH and H groups determines the monosaccharide . • Orientation of OH on Carbon 5 (in Hexoses) confers D (dextro rotatory) or L (laevorotatory) forms • D points right • L points left • Orientation of OH on Carbon 1 (in Hexoses) determines  (down) or  (up)

  7. Numbering 6 5 4 1 3 2

  8. The molecules are isomers, they differ in the orientation of H and OH on C2-4.

  9. Note Fructose differs in the position of the carbonyl – important in forming rings

  10.  down,  up The OH group on the carbon next to the oxygen (C1)

  11. Forming Rings 1 Rings form between C1 and C5. An O atom acts as a bridge (hence the 6 member ring). 2 Complex rearrangement 3 4 5 6

  12. Disaccharides • Two monosaccharides join together with a glycoside bond • Dehydration (condensation) reaction (elimination of water) • e.g. maltose (2 x glucose) •  -D-glucose joined to  -D-glucose • join at the C1 () and C4 atoms • 1-4 glycoside bond

  13.  1,4, glycosidic bond - cellobiose  1,2 glycosidic bond -sucrose  1,6, glycosidic bond

  14. Polysaccharides • 3 major ones of interest • Starch • Glycogen • Cellulose

  15. STARCH • Comprised two components • Soluble part (20%) - AMYLOSE • Continouous unbranched chain of glucose units (up to 300) joined by 1-4 glycoside bonds. • Insoluble part (80%) – AMYLOPECTIN • Shorter 1-4 chains (24-30), with 1-6 branching Starch, being insoluble exerts no osmotic pressure, so is useful as a storage polysaccharide

  16. GLYCOGEN • Animal storage polysaccharide • Similar to amylopectin, • Lower molecular weight • More highly branched • 1-4 chains (up to 10), with 1-6 branching

  17. CELLULOSE • Linear polymer of glucose units (up to 2800) •  1,4, glycosidic bonds • Cellulose fibre - parallel strands held together by hydrogen bonds

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