Structure and function of cell components (i)Carbohydrates (ii)Lipids (iii)Proteins (iv)Nucleic Acids (v)Membranes (vi)Cytoskeleton

Carbohydrates Carbohydrates are chemical structures containing C, H, and O in a ratio of 1:2:1 The general formula is (CH 2 O) n (CH 2 O) n

Monomer Structures of Glucose Glucose Chemical formula = C 6 H 12 O 6 Chemical formula = C 6 H 12 O 6 A Hexose sugar A Hexose sugar Monomer (“single” “part”) / single sugar (monosaccharide) Monomer (“single” “part”) / single sugar (monosaccharide) Isomers of glucose (an isomer has the same chemical composition, but different arrangement) (an isomer has the same chemical composition, but different arrangement) Glucose isomers are usually due to the different arrangement of the carbonyl (C=O) group. Glucose isomers are usually due to the different arrangement of the carbonyl (C=O) group.

Monomer Structures of Glucose cont.. Linear Glucose

Monomer Structures of Glucose cont… Converting between linear and ring isomers C1 loses one of its oxygen bonds C1 loses one of its oxygen bonds C1 gains an OH from C5 C1 gains an OH from C5

Monomer Structures of Glucose cont… α-glucose OH below OH below

Monomer Structures of Glucose cont… β-glucose OH above OH above

Monomer Structures of Glucose cont… Equilibrium of linear and ring forms In solution glucose takes up the shape of least energy, which is the ring form. In solution glucose takes up the shape of least energy, which is the ring form. Equilibrium proportions are: Equilibrium proportions are: 38% α-glucose 62% β-glucose 0.02% linear + others

Disaccharides and their formation A disaccharide is a sugar made up of 2 monomers Glucose monomers are joined together by a glycosidic bond. This is the result of a dehydration (condensation) reaction in which water is a bi-product.

Disaccharides and their formation Maltose Joining of 2 α-glucose molecules Joining of 2 α-glucose molecules Joining occurs between the OH attached to C1 of one ring and OH attached to the C4 of the other Joining occurs between the OH attached to C1 of one ring and OH attached to the C4 of the other

Disaccharides and their formation Maltose cont... Therefore = α1-4 glycosidic bond Therefore = α1-4 glycosidic bond

Disaccharides and their formation Cellobiose Joining of 2 β-glucose molecules Joining of 2 β-glucose molecules Joining occurs between the C1 and C4 carbons of each ring Joining occurs between the C1 and C4 carbons of each ring Note: 1 ring has to be upside down for the OH groups to be side by side. Note: 1 ring has to be upside down for the OH groups to be side by side.

Disaccharides and their formation Cellobiose cont… Therefore = β1-4 glycosidic bond Therefore = β1-4 glycosidic bond

Structure of Polysaccharides Starch Synthesised from α-glucose monomers Contains 2 forms – amylose and amylopectin Amylose Amylose α-glucose monomers joined by α1-4 glycosidic linkages Unbranched Forms a helical shape due to the glycosidic bond bending the molecule slightly

Structure of Polysaccharides Starch cont… Amylopectin Amylopectin α-glucose monomers joined by α1-4 glycosidic linkages Branched Side branches joined on by α1-6 glycosidic linkages

Structure of Polysaccharides Cellulose Made of β-glucose molecules (therefore β1-4 glycosidic linkages) Unbranched Straight chain

Structure of Polysaccharides Glycogen Synthesised from α-glucose monomers (joined by α 1-4 glycosidic linkages) Very highly branched (α 1-6 glycosidic linkages)

Function of Carbohydrates Energy All sugars release energy when respired. All sugars release energy when respired. Excess sugars are stored Excess sugars are storedStorage Starch acts as energy store in plants, glycogen acts as energy store in animals Starch acts as energy store in plants, glycogen acts as energy store in animals Polysaccharides are used for energy storage because of their compact shapes Polysaccharides are used for energy storage because of their compact shapes

Function of Carbohydrates Storage cont… Polysaccharides are hydrolysed (opposite process to dehydration) by enzymes to form glucose when needed Polysaccharides are hydrolysed (opposite process to dehydration) by enzymes to form glucose when needed Polysaccharides are insoluble in water, therefore they do not affect the osmotic balance of the cell. Polysaccharides are insoluble in water, therefore they do not affect the osmotic balance of the cell. (If the equivalent sugar was present, large amounts of water would move in by osmosis) (If the equivalent sugar was present, large amounts of water would move in by osmosis)Structure Cellulose makes up the cell walls Cellulose makes up the cell walls

Learning Activities Read DART pg 25 – 31 Scholar 4.2 Carbohydrates (People needing a brush up on chemistry should also do introduction activities) (People needing a brush up on chemistry should also do introduction activities) Carbohydrates worksheet Advanced Higher Questions Posters Practise the drawing the different molecular structures