Carbohydrates  Aims:  Must be able to state the main forms of Polysaccharides.  Should be able to describe the formation of Polysaccharides.  Could be able to explain why starch and cellulose are suited for their function.

Carbohydrates  60 – 90% of plant dry mass.  General formula C n (H 2 O) m  Main groups are SIMPLE SUGARS and POLYSACCHARIDES.  Used as storage molecules, building blocks and for energy.  Sugars, Starch, Cellulose, Glycogen and Lignin are well known examples.

Monosaccharides  All contain Carbon, Hydrogen, and Oxygen in a ring structure.  Can have different numbers of carbon atoms and different arrangements.  TRIOSE sugars have 3 Carbons  PENTOSE sugars have 5 Carbons  HEXOSE sugars, e.g. Glucose have 6 Carbons.  Monosaccharides are sweet, soluble and have a low molecular mass.  Best known hexose sugars are GLUCOSE and FRUCTOSE.  All hexose sugars have chemical formula C 6 H 12 O 6 but different structural formula – They are isomers.

Triose Sugars  Ketone – Aldehyde –  These can both donate electrons to other molecules = Reducing Agents  Importance of Glyceraldehyde:  Common intermediary compound in photosynthesis and respiration – provides a link  Can be converted to glycerol for lipid synthesis  Involved in intermediary metabolism – e.g. Liver

Pentose Sugars  E.g. Ribose – Formation of RNA ATP energy carriers ATP energy carriers NAD – Electron carrier NAD – Electron carrier  Deoxyribose – Formation of DNA  Ribulose – Involved in carbon dioxide fixation – photosynthesis

Hexose Sugars  Divided into;  Aldoses – Aldehyde group present.  E.g. Glucose and Galactose  Ketones – Ketone group present.  E.g. Fructose  All Hexoses are WHITE, CRYSTALLINE, SWEET compounds, REDUCING SUGARS

Disaccharides  Monosaccharides can join together to form DISACCHARIDES.  These are all white, sweet and crystalline sugars.  Diagram:

Disaccharides NameMonosaccarides PresentBondReducing Agent (Y/N) Maltoseα Glucose + α Glucose1/4Y Lactoseβ Galactose + α Glucose1/4Y Sucroseα Glucose + β Fructose1/2N

Disaccharides  Functions:  Maltose – First product of starch digestion by amylase  Lactose – Milk sugar – Primary source of energy in new born mammals  Sucrose – Found in vacuole – important in turgor maintenance. Soluble so an ideal transport form. Primary energy source in the developed world as a sweetener.

Polysaccharides  α and β glucose molecules produce different polymers.  Starch and Glycogen (storage) are polymers of the α form.  Cellulose (structural) is a polymer of the β form.

Polysaccharides - Starch  Starch – Mixture of ‘soluble’ starch or Amylose and Amylopectin.  Amylose – α helix soluble by forming a colloid by hydrogen bonding to water soluble by forming a colloid by hydrogen bonding to water Traps iodine molecules in helix Traps iodine molecules in helix  Amylopectin – Chain molecule of glucose with branches (1-6 bond) every 10 th glucose.  Amylose helix entangled with Amylopectin branches – Starch is INSOLUBLE

Polysaccharides - Starch  Role:  Energy store in plants – All plant cells and specialised organs.  Starch is an ideal storage compound because it is INSOLUBLE.  Starch is the primary energy source in L.D.C.

Polysaccharides  Glycogen:  Structure similar to Amylopectin but side branches occur MORE frequently.  INSOLUBLE – Energy source in Liver and Muscles.  Cellulose:  1-4 β glucose polymer  Long straight fibrils (unbranched)  Forms regular crystalline lattice due to H-bonds  Function – formation of cell walls, support plant Important source of roughage due to resistance to digestive enzymes.

Complex Carbohydrates  Monosaccharide molecules can be joined to proteins and lipids to form glycolipids and glycoproteins.  Glycoproteins – Cell adhesion Immunological markers Immunological markers  Glycolipids – part of Myelin sheath  Chitin – exoskeleton of insects  Hemicelluloses – Polymer of pentoses Structure of plants Structure of plants

Research  Research one naturally occurring Monosaccharide or Disaccharide:  Chemical formula  Structural formula  Where it is found  Use(s)  synthesis