2016 VJC H2 Biology Prelims Paper 2 Answers

VICTORIA JUNIOR COLLEGE BIOLOGY DEPARTMENT JC2 PRELIMINARY EXAMINATIONS 2016 Higher 2 BIOLOGY 9648/02 Paper 2 Core Paper Answers 14 September 2016 1 (a) (i) Identify structures P and Q and describe briefing their functions. [3]  P – Nucleolus [1/2]  Transcription of ribosomal RNA [1/2]  Site of ribosome assembly [1/2]  Q – Smooth endoplasmic reticulum [1/2]  Site of synthesis of lipids [1/2]  Detoxification of drugs and poisons [1/2]  Stores calcium ions required for contraction in muscle cells [1/2] (ii) Contrast the structure of a lysosome with structure P. [2] Lysosome P (Nucleolus)  Membrane-bound [1/2]  Not membrane-bound [1/2]  Contains hydrolytic enzymes [1/2]  Contains DNA coding for rRNA [1/2] (b) (i) Name a carbohydrate that functions as a storage molecule for T-helper cells.  Glycogen [1] (ii) Describe three structural differences between ce llulose and the carbohydrate in (bi). [3] Cellulose Glycogen  Made up of β-glucose  Made up of α-glucose  Joined by β 1,4 glycosidic bonds  Joined by α 1,4 glycosidic bonds and α 1,6 glycosidic bonds  Unbranched, straight chains  Branched brush-shaped  Alternate subunits rotated 180 o  Alternate subunits in the same orientation  Inter-chain hydrogen bonds present  No cross-linkages between adjacent chains (iii) Explain how the presence of two types of bonds in amylopectin enables it to carry out its function. [2]

1    VJC H2 Biology Paper 2 Preliminary examination 2016     α 1,4 glycosidic bonds between subunits within a branch [1/2]  α 1,6 glycosidic bonds at branch points [1/2]  form branched helical structure  compact for storage function  Both bonds can be broken enzymatically to release α glucose for respiration [1/2]  Hydrolysis of α 1,6 glycosidic bonds breaks up am ylopectin into many branches for more efficient breakdown [1/2] (c) Phosphofructokinase is an allosteric enzyme. Explain how the presence of an allosteric inhibitor affects the enzymatic activity of an allosteric enzyme. [2]  Allosteric inhibitor binds to allosteric site [1/2]  Causes the enzyme conformation to change to inactive state [1/2]  Active site not complem entary to substrate [1/2]  Prevent effective collision and formati on of enzyme-substrate complex [1/2] 2. The diagram below shows an enzyme involved in the activation of tRNA for translation in prokaryotes. (a) (i) Explain the mode of action of this enzyme [3]  amino-acyl tRNA synthetase;  has a specific active site that is  complementary to specific tRNA anticodons and a specific amino acid  Ref. to induced fit theory  catalyses the attachment of a specific am ino acid to the 3’ stem of the tRNA in the formation of the amino-acyl tRNA complex  by lowering the activation energy of the reaction  through the formation of an enzyme structure complex (ii) Explain the significance of