2018 Collated Biomolecules & Enzymes STQ QP

2018 Collated Biomolecules and Enzymes (DNA, Gene Expression) STQ 2018 / H2 / AJC PRELIM / P2 Q21Fig. 1.1 shows the effect of pH on the activity of a protease enzyme at the optimal temperature of 37oC. Fig. 1.1(a)Draw, on Fig. 1.1, the approximate shape of the curve if the same experiment is conducted at 25oC.[1](b)Explain with reasons the shape of the curve you have drawn.……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….[2]

(c)Using information from the graph, explain why proteases stored in vesicles with pH 7.2 cannot break down vesicular membrane proteins and suggest how these proteases can be activated through increase in pH.……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….……………………………………………………………………………………………….[6][Total: 9]

2018 / H2 / EJC PRELIM / P2 Q1 ( Cancer Eukaryotic Cell Structure)2The synthesis of collagen is shown in Fig. 1.1. CProcess B(tropocoFig. 1.1(a)(i)Describe two important functions of structure A in the synthesis of collagen. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………………………………………………………...[2](ii)Tropocollagen leaves the cell to be assembled to form collagen fibrils via Process B. Outline Process B.

……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[3](b)Suggest how chemical modification such as hydroxylation in organelle C results in collagen having a high tensile strength. …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[2]Fig. 1.2 shows two electron micrographs. One of the electron micrograph shows part of a normal cell while the other electron micrograph shows part of a cancer cell. The white arrows point to an organelle within the cell. The appearance of this organelle in both cell types were visibly different. The cancer cell had a higher activity than the normal cell. Organelle (indicated by white arrows) in a normal cellOrganellarrows) iFig. 1.2(c)(i)Describe the visible difference between the organelle indicated by the white arrows in Fig. 1.2, between the cancer cell and the normal cell. ………………………………………………………………………………………………………………………………………………………………………………………………………[1](ii)Account for the higher activity of the cancer cell.

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………[2][Total: 10]2018 / H2 / EJC PRELIM / P2 Q23The rate of glycolysis is regulated by the action of ATP on the enzyme phosphofructokinase (PFK), the thenzyme in the glycolysis pathway. PFK catalyzes the formation of fructose 1,6-bisphosphate from fructosephosphate and ATP.A graph of PFK against F6P concentration would exhibit the ‘sigmoidal curve’ typical of allosteric enzymes.Fig. 2.1 shows the effect of substrate F6P (fructose 6-phosphate) concentration on the activity of PFKdifferent ATP concentrations. PFK is an allosteric enzyme with a quaternary structure that is inhibited by hlevels of ATP. High levels of ADP and AMP will increase activity of the enzyme. F6PFig. 2.1(a)(i)With reference to PFK, explain the term ‘allosteric enzyme’. ……………………………………………………………………………………………………… ...…………………………………………………………………………………………………[1](ii)On Fig. 2.1, label the graphs which reflect low ATP and high ATP concentrations respective[1](b)Enzyme researchers have used a model of allosteric enzyme mechanism called the ‘symmetry model’

explain the action of PFK. F6P binds with great affinity only to the active state but not to the inactive staBinding of one F6P molecule will progressively shift PFK structure from the inactive state to the active state.A graph of PFK against F6P concentration would exhibit the ‘sigmoidal curve’ typical of allosteric enzymes. (i)Explain how the binding of a molecule like AMP to PFK can increase the activity of PFK. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ..…………………………………………………………………………………………………[2](ii)The enzymatic mechanism in PFK is similar to that of the oxygen-binding mechanism of the transpprotein, haemoglobin. Sketch the shape of the oxygen binding graph for haemoglobin at increasconcentrations of oxygen in the space below. [1] % oxygen saturation of haemoglobin / %Oxygen partial pressu(iii)Using your knowledge of the structure of haemoglobin, explain the shape of the graph you drew in (ii).……………………………………………………………………………………………………..……………………………………………………………………………………………………..……………………………………………………………………………………………………..……………………………………………………………………………………………………..……………………………………………………………………………………………………..…………………………………………………………………………………………………..[3](c)Explain the significance of regulation of PFK by ATP to AMP ratios.

……………………………………………………………………………………………………………...……………………………………………………………………………………………………………...……………………………………………………………………………………………………………...…………………………………………………………………………………………………………...[2][Total: 2018 / H2 / JJC PRELIM / P2 Q24Fig. 2.1 shows a triglyceride molecule. Fig. 2.1(a)(i)State the names of the two types of molecules that undergo condensation reactions to form a triglyceride. [2]________________________________________________________________________________________________________________________________(ii)Describe what is meant by a condensation reaction. [2] ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

(iii) The triglyceride in Fig. 2.1 is saturated.Explain how the structure would be different for an unsaturated triglyceride. [3] ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________(b)The eukaryotic cell surface membrane contains phospholipids, cholesterol and proteins.(i)Describe how a phospholipid molecule differs from a triglyceride molecule. [2]________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________(ii)Describe the roles of cholesterol in eukaryotic cell surface membranes. [2]________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

(c)The respiratory quotient, RQ, is used to show which substrate is being metabolised by cells. It can be determined using the equation below. Lauric acid is a saturated fatty acid found in coconuts and has a chain of 12 carbon atoms.(i)Complete the equation below which outlines the aerobic respiration of lauric acid. [1]C12H24O2 + ……. O2 12CO2 + 12H2O(ii)Calculate the RQ value for