RI Nov 13 H2P2 Ans

Raffles Institution Nov 2013 (H2 Biology) Paper 2 (for 9744 syllabus) 2017 Nov 2013 H2 Bio Paper 2 N13P2Q1 (a) Describe the processes that occur in the Golgi body. [3] 1. Glycosylation* where oligosaccharides/short sugar chains are added to proteins and lipids to form glycoproteins and glycolipids respectively; 2. Modification of existing glycoproteins and glycolipids made in the endoplasmic reticulum by modifying the existing oligosaccharide / cleaving sugar molecule(s) from the oligosaccharide; 3. In plant cells, Golgi body is the site for synthesis of polysaccharides such as pectin (a component in plant cell wall) and then transported in vesicles to the cell membrane; 4. Sorting* of proteins into different kinds of vesicles to target the proteins to different parts of the cell or for secretion; (b) Describe the role of vesicles that fuse with the forming face of the Golgi body. [3] 1. Vesicles that bud off from rough endoplasmic reticulum (RER) carry proteins; 2. and bud off from smooth endoplasmic reticulum (SER) carry lipids; 3. These vesicles are targeted to fuse to cis-face of Golgi by microtubules of the cytoskeleton/proteins; (c) Outline two roles for the vesicles that are formed at the maturing face of the Golgi body. [4] 1. Lysosome / lysosomal vesicles; 2. fuses with vesicles/vacuoles formed by endocytosis to digest the contents (e.g. foreign particles) within the vesicles/vacuoles; (pt 1 & 2 = 2 marks) 3. Exocytic vesicles; 4. fuses with plasma membrane to release enzymes outside of cell by exocytosis to breakdown extracellular content / fuses with plasma membrane to release contents outside of cell by exocytosis; (pt 3 & 4 = 2 marks) 5. Secretory vesicles; 6. fuses with plasma membrane to release contents upon receiving signal; (pt 5 & 6 = 2 marks) Any 2 pairs of points N13P2Q2 (a) State what happens if a cell loses control of the cell cycle. [1] 1. Uncontrolled cell proliferation; (b) With reference to Fig. 2.1, suggest how the dysregulation of checkpoints of cell division may occur. [3] 1. Point mutation of S-cyclin gene to cause change in amino acid sequence of S- cyclin protein, thus S-cyclin is resistant to degradation / Point mutation of M-cyclin gene to cause change in amino acid sequence of M-cyclin protein, thus M-cyclin is resistant to degradation; 2. Prolonged activation of M-CDK and S-CDK to cause more rounds of cell division thus excessive cell proliferation; 3. Gene amplification of CDK gene to increase number of copies of gene resulting in increase amount of CDK protein; 4. Increase number of binding sites for S-cyclin/M-cyclin to form increase amount of active CDK;

Raffles Institution Nov 2013 (H2 Biology) Paper 2 (for 9744 syllabus) 2017 (c) (i) Name o