RI N22 H2 P2 Answers

2022 H2 Paper 2 Section A Answer all questions 1(a) Outline the main features of the cell theory. [3] 1. The cell is the smallest unit of life ; 2. All known living organisms are made up of cells ; 3. All cells come from pre-existing cells ; (b) (i) Complete Table 1.1 to show the name and function of the structures labelled A, B, C and D in Fig. 1.1. [4] label name function A mitochondrion Site of aerobic respiration* where ATP* synthesis occurs; B nucleus Contains DNA where transcription* occurs to produce mRNA*; C Golgi* body/apparatus Modify lipids and proteins by glycosylation* to form glycolipids and glycolipids respectively; To sort and package proteins into different vesicles and target the proteins to different parts of the cell or for secretion out of cell; D Rough endoplamic reticulum Translation* of mRNA to protein/ protein synthesis by bound ribosomes*; Glycosylation* of proteins; Transportation of proteins in transport vesicles to the Golgi apparatus; (ii) Compare the process of asexual reproduction in yeast with binary fission in bacteria. [2] 1. Similarity – both result in 2 genetically identical* daughter cells; 2. Difference – budding involves the evagination* of the cell surface membrane to form a daughter cell but binary fission involves the invagination* of the cell surface membrane to separate the 2 daughter cells; [Total: 9]

2 (a) With reference to Fig. 2.1, describe the effect of increasing lopinavir concentration on the inhibition of HIV protease. [3] 1. As the concentration of lopinvar increased, the percentage inhibition increased; 2. From 0.0 to 0.4 µmoldm-3 lopinavir concentration, there is a gradual increase in percentage inhibition, from 0.0 to 8.0%; 3. From 0.4 to 1.6 µmoldm-3 lopinavir concentration,there is a steep increase in percentage inhibition from 8.0 to 97.0%; 4. From 1.6 to 2.4 µmoldm-3 lopinavir concentration, the pecentage inhibition starts to plateau from about 97.0 to 99.0%; (b) Explain how lopinavir inhibits HIV protease. [4] 1. Lopinavir has a 3D conformation that is complementary in shape and charge to the active site* of HIV protease; 2. and lopinavir has a similar shape as the substrate/polyproteins; 3. Lopinavir competes with the substrate/polyproteins for the active site of HIV protease and prevents the substrate from binding to active site and hence reduces the rate of reaction; 4. The binding of the inhibitor to the active site is not permanent/reversible; 5. However, at high substrate concentration, the effect of the inhibitor can be overcome and Vmax can be reached; (c) Translation of viral RNA in cells infected with the human immunodeficiency virus (HIV) results in large polypeptides known as polyproteins. HIV protease cuts each of these viral polyproteins into smaller molecules. Suggest how inhibition of HIV protease may limit the ability of HIV to reproduce. [3] 1. If HIV protease activity i