VJC 2021 H2 Bio 9744 P2 Answers

1 Victoria Junior College Biology Department 2021 Prelims H2 Paper 2 – Proposed Answers 1 (a) Outline how the enzymes are packaged into vesicles and release to the outside of the cell. [4] 1. Enzymes synthesised in rough endoplasmic reticulum (rER) are packaged into transport vesicles pinched off from rER and fuse with cis/forming face of Golgi apparatus; 2. At Golgi apparatus, modification, sorting and packaging of enzymes occur; 3. Secretory vesicles (A: Golgi vesicles) containing enzymes buds off trans/maturing face of Golgi apparatus; 4. Secretory vesicles move to and fuse with cell surface membrane, releasing the enzymes via exocytosis; [Points 5 and 6 – 1m max] 5. Vesicles move towards cell surface membrane with the help of microtubules; 6. ATP is required for exocytosis; (b) Explain how the structure of the vesicle allows it to serve its function shown in Fig. 1. 1. [3] 1. Structure of vesicle: made up of a phospholipid bilayer; 2. Phospholipids (PL) provides fluidity, which allows for fusion of vesicle membrane with cell surface membrane for release of enzymes to the outside of the cell; 3. The hydrophilic phosphate heads of the PL interact with the aqueous environment/cytoplasm and within the vesicle for stability; Or hydrophilic phosphate heads of the PL interact with the aqueous environment of the cytoplasm to allow for transport of vesicles within the cell; 4. Hydrocarbon tails of the phospholipids forms the hydrophobic core of the membrane prevents the enzymes from moving out of the vesicles while they are being transported; 5. AVP; (c) Suggest and explain one modification to the vesicles to allow them to deliver the drugs to specific cells. [2] • Modification to vesicle [Any one below] ➢ Add glycoproteins/ glycolipids add to the phospholipids on the outer surface of the vesicle; ➢ Attach carbohydrate specific epitopes/ antigen to the phospholipids on the outer surface of the vesicle; which will recognise and bind to specific receptors found only on the specific cells by complementary shape; • How uptake can take place: (binding of glycoproteins on vesicle to specific receptors on specific cell results in ) receptor-mediated endocytosis/ endocytosis/ fusion, allowing uptake by cells;

2 (d) Describe two differences between the release of enzymes shown in Fig 1.1 and the process in which flu virus leave the host cells. [2] Release of enzymes Process which flu virus leave the host cells [Any 1 of the following] • Exocytosis • involves fusion of vesicle membrane with cell surface membrane • Addition of cell membrane • Budding • Involves evagination of host cell membrane; • Involves removal/ loss of cell membrane; R: Budding vs no budding, fusion vs no fusion, loss vs no loss of membrane etc – when there is an equivalent process that occurs, students should describe the process. [Any 1 of the following] • Vesicle can exit / leave / fuse