2018_Cancer_STQ_MS

2018 Cancer STQ MS2018 / H2 / AJC PRELIM / P2 Q51Skin cancer cells may be grown in culture and examined using the technique of immunofluorescence in which antibodies are used to attach fluorescent dyes to specific molecules within the cells. Fig. 5.1 is an immunofluorescent light micrograph of skin cancer cells. A particular type of protein is stained with the dye and appears as pale regions in the skin cancer cells. Fig. 5.1 (a)(i)Before the skin cancer cells could be stained with antibodies, the cells had to be fixed and treated with a mild detergent to increase the permeability of the cell surface membranes.Explain the purpose of this step.Membrane has a hydrophobic core; Antibodies that is polar in nature are unable to pass thru the membrane.Accept: too large to pass through the membrane[2](ii)There are two cells in the process of dividing. Each of these cells has two areas stained heavily, labelled A on Fig. 5.1.Suggest the identity of these two areas and outline their functions in these cells.spindle apparatus / spindle fibresaccept: spindle / microtubules / tubulin / centrioles / microtubule organising centres / MTOCs Attach to centromere/kinetochore protein of the chromosomes; Can elongate/shorten to move chromosomes during mitosis[3]

(accept if students describe function of spindle fibre in prophase/anaphase); Accept if centrioles given as identityforms poles of the cell ;organises the spindle ;(iii)Suggest why the proteins stained in the cytoplasm of the non-dividing cells in Fig. 5.1 are not evenly distributed.forming cytoskeleton/actin filaments in the cells. to maintain shape of cells.to help to support/anchor organelles in different parts of the cells. For movement of transport vesicles/secretory vesicles[1](b)Explain two ways in which the behaviour of chromosomes in prophase of meiosis I differ from prophase of mitosis. During prophase I, homologous chromosomes pair up. However, in prophase of mitosis, homologous chromosome doses not pair up; During prophase I, chiasmata formed and crossing over between non-homologous sister chromatids occurs. However, in mitosis, no crossing over occurs. [2](c)Some chemicals known to inhibit the cell cycle are used as drugs for the treatment of cancer. A particular drug was found to be most effective when applied to cancer cells in the G2 phase of the cell cycle. Suggest the possible mechanism of this drug. Inhibit the condensation of chromosomes; Inhibit the replication of centrioles/centrosome; Inhibit the organisation of spindle fibres within the cells; Reject: “inhibit protein synthesis” unless specifically mention that inhibition of synthesis of proteins required for chromosome condensation; Compulsory point: Induced a G2 check point and prevent the cells from entering mitosis; [3] [Total: 11]

2018 / H2 / MJC PRELIM / P2 Q5QUESTION 2Fig. 5.1 shows the stages involved in the synthesis of a p53 protein in a eukaryotic cell. Fig. 5.1(a)Name the structure H. [1]Promoter