RI Nov 14 H2P2 ans

Raffles Institution Nov 2014 (H2 Biology) Paper 2 (for 9744 syllabus) 2017 Nov 2014 H2 Bio Paper 2 N14P2Q1 (a) With reference to Fig 1.1, describe the curve between points A and B [2]. 1. As temperature increases from 350C (pt A) to 500C, the rate of reaction of enzyme increases gradually from 0 to 8a.u. 2. However, from 500C to 650C (pt B), there is a steeper increase in rate of reaction of enzyme from 8a.u. to 65 a.u. This increase is about 7 times that of the increase in rate from 350C to 500C . (b) Explain why the reaction rate changes from: (i) A to B [3] 1. As temperature increase from 35 0C (at A) to 65 0C (at B), there is increase in kinetic energy of the enzyme and substrate molecule. 2. which increases frequency of effective collisions* between substrate and enzyme thus rate of formation of enzyme-substrate complex* increases ; 3. increasing temperature also increases the number of molecules having sufficient energy to overcome the activation energy* barrier to form the products of reaction; (ii) C to D [3] 1. At 750C (pt C), the optimum temperature* of Taq polymerase, there is greatest number of molecular collisions and hence max rate of reaction 2. As temperature increase further to 850C (pt D), which is beyond optimum temperature, thermal agitation / vibration of enzyme molecule breaks hydrogen, ionic bonds and other weak interactions that stabilizes the 3D conformation resulting in denaturation* 3. The enzyme active site* no longer complementary in shape* and charge to the substrate and the rate of reaction decreases steeply from maximum rate of 95 a.u. to almost 0a.u. (c) Suggest how the structural features of Taq polymerase make it thermostable [2] 1. More Cysteine* residue may be present in the Taq polymerase allowing the formation of more disulphide linkages* with another cysteine residue to maintain the 3D conformation 2. Disulphide linkages are strong covalent bonds difficult to be broken by high temperature 3. Hence the 3D conformation of active side maintained \ N14P2Q2 (a) Give the full name of the bond holding the two glucose molecules together in the way shown. [2] 1. -1,4-glycosidic bond (b) Describe how this bond may be broken to release two molecules of glucose. [2] 1. Addition of water in hydrolysis* reaction 2. Enzymatic action of maltase 3. Acid hydrolysis by heating it with hydrochloric acid (either 2. or 3.)

Raffles Institution Nov 2014 (H2 Biology) Paper 2 (for 9744 syllabus) 2017 (c) (i) Describe the arrangement of phospholipids in cell membranes. [2] 1. 2 layers of phospholipid molecules in a bilayer 2. With the hydrocarbon tails facin