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2007mcb2001s - University of Cape Town Department of...

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University of Cape Town Department of Molecular & Cell Biology Course Code: MCB2001S Course Name: Molecular Biology & Physiological Biochemistry Paper: 1 (Theory) Date: 2 Nov 2007 @ 17h00 No.of pages: 14 Marks: 136 Time: 3 Hours Venue: Zoology 1 Additional: Graph paper and Data Sheet ANSWER ALL THE QUESTIONS In the interest of economy please write on both sides of the exam script Please answer each section in a different answer book. Multiple choice questions are subject to negative marking Section 1 : Dr Jerry Rodrigues 100 Marks Carbohydrates: (20 marks) 1a) Draw the Haworth structure of α -D-glucopyranose. (3) b) Now draw the mirror image (Haworth) of the α -D-glucopyranose. (3) c) What is the name of the compound that is the mirror image of α -D-glucopyranose? (2) d) Would you refer to these two compounds as epimers or enantiomers? (1) 2. Draw the structure of the disaccharide glucosyl α (1 6)-galactopyranose in the β -anomeric form. (6) 3. The carbohydrate portion of some glycoproteins may serve as a recognition site and in some cases as a timing device for protein degradation. Two serum glycoproteins (A and B) are partially depicted below with attached oligosaccharide chains and showing the N- and C-termini. Please answer the questions that follow: 1 A. B.
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(a) What is the identity of the amino acid (marked X in the boxes) to which the oligosaccharide chains are attached? (1) (b) Are the oligosaccharide chains bound to the protein via O-glycosidic bonds or N- glycosidic bonds? (1) (c) What is another name for sialic acid? (1) (d) Which of the two glycoproteins (A or B) will bind to the asialoglycoprotein receptor on the liver cell? (1) (e) Which of the two glycoproteins (A or B) is not yet earmarked for degradation in the lysosome? (1) Immunology: (20 marks) 1. Define the following terms: (a) hapten (b) affinity maturation (c) plasma cell (d) perforin (4) 2. When sodium dodecylsulfate (SDS) polyacrylamide gel electrophoresis of a monoclonal antibody preparation is conducted in the absence of β -mercaptoethanol, a single sharp band appears. When the antibody preparation is treated with β - mercaptoethanol, two bands appear. Why is this the case? (2) 3a) What mechanisms generate the three hypervariable regions (complementarity- determining regions) of immunoglobulin heavy and light chains? (3) b) Why is the third hypervariable region (CDR3) more variable than the other two (CDR1 and CDR2)? (3) c) Why is there greater diversity within the CDR3 of the heavy chains compared with that of the light chains? (2) 4. Indicate whether each of the following statements is true ( T ) or false ( F ). (0.5 marks each) a) A large protein antigen generally can combine with many different antibodies. b) A hapten can stimulate antibody formation (bound to BSA) but cannot then combine with the isolated antibody. c) Major histocompatibility complex (MHC) genes play a major role in the immune response to an antigen.
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