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Biological Molecules ‘what you need to know!’ MONOMER – single repeating units that…… ……are joined together to form POLYMER. MONOMER POLYMERISATION POLYMER Polymers Monomers Polysaccharides Glucose Proteins Amino acids Lipids? Glycerol & fatty acids CARBOHYDRATES CARBOHYDRATES MONOSACCHARIDES DISACCHARIDES POLYSACCHARIDES MONOSACCHARIDES - A single sugar unit - Sweet and soluble - Contain carbon, hydrogen & oxygen - Classified according to the number of carbons a molecule has: -TRIOSE – 3 carbons -PENTOSE – 5 carbons and -HEXOSE – 6 carbons MONOSACCHARIDES Three common sugars share the same molecular formula: C6H12O6. Because of their six carbon atoms, each is a hexose. They are: • glucose, the immediate source of energy for cellular respiration • galactose, a sugar found in milk • fructose, a sugar found in honey and fruits. MONOSACCHARIDES – which is which? MONOSACCHARIDES – which formula? Molecular formula – C6H12O6 or C3H6O3 or C5H10O5 Structural formula – Although galactose, glucose and fructose share the same molecular formula (C6H12O6), the arrangement of atoms differs in each case. Substances such as these three, which have identical molecular formulas but different structural formulas, are known as structural isomers. Pentose and hexose sugars are drawn in two forms straight chain forms Ring forms 3D model Carbon Hydrogen Oxygen 2D model C6H12O6 Glucose: Going from chain to ring form How the chain closes to form a ring in solution inside cells. Observe the atoms involved (highlighted in colour). GLUCOSE comes in 2 forms, according to how the ring closes. WARNING! A single detail like this one makes all the difference. The position of the OH group on C1 will determine the type of polysaccharide it will form and in turn, the functions it will have in a cell. Remember this as you study polysaccharides. Here this H is above the carbon 1. This is called α (alpha) glucose. Here this H is below the carbon 1. This is called β (beta) glucose. Structural Isomers Both these molecules are glucose. Both have a molecular formula of C6H12O6. But they are structurally different and will have different functions in a cell. Biological role of monosaccharides As an energy source….. •A large amount of energy is stored between the C-H bonds •This is released to form ATP •ATP is the energy currency of the cell As building blocks….. •Repeated glucose molecules build up; starch & glycogen •Ribose (5C) forms part of RNA •Deoxyribose (5C) forms part of DNA •Vitamin C (ascorbic acid derives from glucose) DISACCHARIDES Two monosaccharides can be linked together to form a "double" sugar or disaccharide. Three common disaccharides: sucrose — common table sugar = glucose + fructose lactose — major sugar in milk = glucose + galactose maltose — product of starch digestion = glucose + glucose Although the process of linking the two monomers is rather complex, the end result in each case is the loss of a hydrogen atom (H) from one of the monosaccharides and a hydroxyl group (OH) from the other. The resulting linkage between the sugars is called a glycosidic bond. The molecular formula of each of these disaccharides is C12H22O11 (2 C6H12O6 − 1 H2O) DISACCHARIDES Two well-known examples: maltose (used in the making of beer) and sucrose (table sugar) Forming disaccharides: maltose 1. Two α glucose molecules meet. 2. The OH from C1 & H from C4 react to form a molecule of water. This is called a condensation reaction. 3. The C1 is joined to the C4 by the O left. 4. The bond between the two joined glucoses is called glycosidic bond. In this case: α1,4 glycosidic bond. Forming disaccharides: sucrose 1. An α glucose and a fructose molecule meet. 2. The OH from C2 in the fructose & the H from C1 in the glucose react to form a molecule of water. This is called a condensation reaction. 3. The C1 is joined to the C2 by the O left. 4. The bond between these two joined monosaccharides is called glycosidic bond. In this case: α1,2 glycosidic bond. POLYSACCHARIDES • Polymers with subunits of monosaccharides • Made by repeated condensation reactions • Normally thousands of monomers long • Polysaccharides are not sugars STARCH CELLULOSE GLYCOGEN Starch • Polymer of α-glucose. • Plant storage polysaccharide. • Made up of two types of substances: 1) Amylose + 2) Amylopectin Spiral structure of Amylose Amylose •Condensation reactions between α glucose with 1-4 links. •Formed from thousands of condensation reactions that form coiled springs. Amylopectin Mostly 1-4 links. Some 1-6 links. Amylopectin • Condensation reactions between α glucose (1-4 links). • Coiled springs with a branched structure are formed (branches of 1-6 links). 1-6 links form a branch structure 1-4 links form a helical structure Starch grains are a mixture of amylose & amylopectin Starch is a polysaccharide Starch it is a insoluble store of glucose Starch is only found in plant cells, the animal cells equivalent is called glycogen. Glycogen It has 1-4 links and 1-6 links the storage polysaccharide in animals found in liver and muscles Cellulose • Present in plant cell walls. • It is a polymer of β glucose. • It is formed by parallel chains. • Has a slow decomposition. • It is mechanically very strong. • It is the most abundant organic molecule on the planet. Cellulose • C1-4 links make up this polysaccharide. • When the C1 and react, one glucose molecule needs flips through 180o. • This structure has H bonds holding the parallel chains together. • This subtle difference makes cellulose so strong Structural differences between starch, glycogen and cellulose CAN YOU STATE THREE DIFFERENCES BETWEEN STARCH AND CELLULOSE? CAN YOU STATE THREE DIFFERENCES BETWEEN STARCH AND GLYCOGEN? AND BETWEEN GLYCOGEN AND CELLULOSE?