9744 H2 Bio J1 & J2 compilation notes (JPJC)

Carbohydrates Structure & properties of α- glucose and β- glucose - Reducing sugars: carbohydrates that act as reducing agents due to free aldehyde or ketone groups - Monosaccharides: Small, crystalline Dissolve easily in water (due to polar –OH groups → readily form H bonds with water) - α- glucose: –OH group on Carbon 1 projects below the plane of the ring - β- glucose: –OH group on Carbon 1 projects above the plane of the ring Formation & breakage: 1. Type of bond formed 2. Between which molecules 3. Between which functional group 4. Condensation/hydrolysis 5. Addition/removal of water 6. Catalysed by (enzyme) Formation Breakage E.g. α-1, 4 glycosidic bond forms between the –OH group of carbon 1 of one α- glucose monomer and the –OH group of carbon 4 of another α- glucose monomer. This is a condensation rxn with the removal of 1 water molecule and is catalysed by enzymes. E.g. α-1, 4 glycosidic bond between the –OH group of carbon 1 of one α- glucose monomer and the –OH group of carbon 4 of another α- glucose monomer is broken. This is a hydrolysis rxn with the addition of 1 water molecule and is catalysed by maltase.

Structure and properties of: Starch (amylose & amylopectin) Structure: Function: Amylose (is an unbranched chain structure that) consists of many α- glucose residues linked by α-1, 4 glycosidic bonds Glycosidic bonds in amylose can be hydrolysed easily → release of a large number of glucose monomers → oxidised during respiration to produce large amt of ATP. Starch acts as an accessible source of glucose. The angle of these bonds causes the chain to coil helically into a more compact shape, allowing the packing of many glucose molecules per unit volume Due to large number of glucose molecules present, starch (amylose) serves as a good energy source in plants → glucose is oxidised during respiration to produce ATP Most –OH groups are projected into the interior of the amylose helix, hence there are no free –OH groups to form hydrogen bonds with water → insoluble molecule The insoluble nature of starch (amylose) prevents its diffusion out of the cell → does not change the water potential within the cell. Starch suitable as an energy storage molecule Amylopectin has a backbone of α- glucose residues held tgt by α-1,4 glycosidic bonds. It is highly branched with side chains formed by α-1,6 glycosidic bonds Many branched ends allow many hydrolytic enzymes to act on the branched ends at any one time → amylopectin easily broken down into glucose monomers to be used as respiratory substrates. Amylopectin serves as an accessible source of glucose Cellulose Structure: Function: A cellulose molecule consists of a long chain of β- glucose residues linked by β-1, 4 glycosidic bonds which make the cellulose chain straight Successive β- glucose residues are rotated 180° with respect to its adjacent residue → –OH groups projecting outwards from each cellulose chain in all directions Hydrogen bonds are formed between the –OH groups of neighbouring cellulose chains lying in parallel → extensive cross-linking that binds the chains rigidly together (in bundles of 60-70) form microfibrils and macrofibrils which confer high tensile strength, stability and support Cellulose is the main structural component of plant cell walls. The high tensile strength of microfibrils → prevents plant cell from lysing when water enters by osmosis As a plant cell inflates with water, pressure develops inside → turgid → help support plants which lack wood Arrangement of fibres around the cell helps to determine the shape of the plant cell as it grows

Most –OH groups involved in formation of H bonds btwn cellulose chains → fewer –OH groups available for H bonding with water. Large molecule → insoluble in water Macrofibrils arranged in several layers running in diff directions Allows cell wall to remain permeable to water and other solutes Glycosidic bonds in cellulose are not easily hydrolysed unless specific enzymes are present Serve as a good structural molecule Glycogen Structure: Function: Glycogen has a backbone of α- glucose residues held together by α-1, 4 glycosidic bonds, allowing the packing of many glucose molecules per unit volume Due to the large number of glucose molecules present, glycogen serves as a good energy source in animals, as glucose is oxidised during respiration to produce ATP Glycogen is highly branched with side chains formed by α-1, 6 glycosidic bonds Many branched ends allow many hydrolytic enzymes to act on the branched ends at any one time → glycogen can be easily broken down into its glucose monomers (used as respiratory substrates) Glycogen serves as an accessible source of glucose The glycosidic bonds in glycogen can be hydrolysed easily Release of a large number of glucose monomers → oxidised during respiration to produce a large amount of ATP. Glycogen acts as an accessible source of glucose Glycogen is a large polysaccharide, which makes it insoluble in water Large and insoluble nature of glycogen prevents its diffusion out of the cell → does not change the water potential within the cell → glycogen suitable energy storage molecule

Lipids Insoluble in water, dissolve readily in organic solvents Proportion of oxygen is much less in Lipids than Carbs Structure and properties of glycerol and fatty acids Glycerol(C3H8O3): - 3 carbons bonded to –OH - Eah –OH can condense with a fatty acid - Polar, hydrophilic, soluble in water (presence of –OH groups, form H bonds) Fatty acids (R.COOH): - R: long hydrocarbon chain (differs) - Non-polar, hydrophobic, insoluble in water (presence of non-polar hydrophobic hydrocarbon chain, unable to form H bonds with water) - Saturated: Max no. of H atoms Each C atom is joined to the next by single covalent bonds - Unsaturated: At least 1 carbon-carbon double covalent bond Causes kinks in hydrocarbon chain Kinks: unsaturated fatty acids cannot pack closely tgt, resulting in weaker hydrophobic interactions btwn fatty acid molecules. Less thermal energy needed to disrupt these weak hydrophobic interactions to bring abt change in state (solid to liquid). → unsaturated fatty acids hv low b.p. than saturated. - Longer hydrocarbon chains: more extensive hydrophobic interactions, more heat to disrupt hydrophobic interactions Formation and breakage of ester bonds Formation (esterification): Breakage (saponification: basic/alkaline): An ester bond forms between one (hydroxyl) –OH group of glycerol and one (carboxyl) –COOH group of a fatty acid by condensation with the removal of 1 water molecule, catalysed by enzymes. An ester bond between one (hydroxyl) –OH group of glycerol and one (carboxyl) –COOH group of a fatty acid is broken by hydrolysis with the addition of 1 water molecule, catalysed by enzymes/lipase. (addition of acid/base)

Structure and properties o