Biochemistry End of Year Exam — 2014 (Past OmpathStudy

Biochemistry End of Year Exam — 2014 (Past Paper) University of Nairobi Level 1 Biochemistry end-of-year exam, 2014. Scanned original exam paper, reproduced as page images — questions only. --- SECTION A (30 MARKS): Attempt any THREE Questions. 1. The Henderson - Hasselbalch equation is important in the calculation of a pH of a buffer solution. a) With a specific, physiological example, explain the term "buffer solution". (2 Marks) b) Derive the Henderson Hasselbalch equation using a hypothetical weak acid HA. (3 Marks) c) How many grams of acetic acid ($\text{CH} 3\text{CO} 2\text{H}$) and sodium acetate are needed to make up to one litre of a 50 mm acetate buffer with a pH of 5.0. $\text{ka} = 1.75 \times 10^{-5}$ (4 Marks) 2. (a) State 4 functions of carbohydrates. (4 Marks) (b) Explain the basis of reduction tests as a means of identifying sugars in unknown solutions. (2 Marks) SECTION A: Attempt any THREE Questions (30 Marks) 1. Hyperammonemia is lethal and can result in serious mental retardation. Describe the main pathway for removal of ammonia from the body. 2. With regards to glycolysis; a) Describe in detail, the reactions catalysed by kinases b) With relevant reaction(s), distinguish between aerobic and anaerobic glycolysis. c) Which of the two types of glycolysis proceeds with a higher overall standard free energy ($\Delta G^{01}$)? Why? 3. (i) What are enzymes? (ii) Describe the factors which affect the rate of enzymatic reactions. 4. (a) Briefly discuss fate of amino acid pool. (b) Outline metabolic circumstances under which amino acids undergo oxidative deamination and list 4 human disorders associated with amino acids catabolism. 5. (a) Explain the term "Genetic code is degenerate". (b) Explain 'Wobble Hypothesis' showing clearly all the permitted interactions. (c) With regards to ribosomes:- (i) Differentiate between prokaryotic and eukaryotic types (ii) Explain the biological role in living organisms. SECTION B: Answer ALL questions in the spaces provided (30 marks) 1. Synthesis of amino acids is mainly catalyzed by enzymes called which catalyses the transfer of an amino group from an amino acid to a keto acid via a process called . Nevertheless, amino acids can also be catabolized by various pathways. For instance, the catabolism of branched amino acids namely isoleucine, leucine and initially share the first, second and third reactions in their pathways. Deficiency in one of the common enzymes namely leads to a disease called . Catabolism of branched amino acid which is classified exclusively as produce a ketone namely whereas the catabolism of isoleucine result in both 2-carbon and 4-carbon citric acid cycle intermediates namely and respectively. 2. To enter the glycolytic pathway, , , and are firstly converted to , , and respectively. They all end up as a common product namely and from which a high-energy compound known as is formed. 3. The following graph represents a titration curve for the amino acid, lysine. answer the following questions (a-h) choosing answers I-VIII (a) Identify all the $\text{pK} \text{a}$ values on the lysine titration curve [0.75 marks] (b) At which points does lysine have maximum buffering capacity? [0.95 marks] (c) Would lysine have a good buffering capacity at pH 7.6? Explain briefly................................................................................... ......................................................................................................... [1 mark] (d) Which point corresponds to pI of lysine? [0.5 marks] (e) At which point has the carboxyl group been completely titrated? [0.5 marks] (f) At which pint is lysine completely titrated (i.e. all protons neutralized)? [0.5 marks] (g) At which point is the average net charge of lysine equal to -1? [0.5 marks] (h) At which pint is the average net charge of lysine equal to 0? [0.5 marks] 4. Statement Answer :--- :--- (i) Name a 'stop' code for protein biosynthesis UAG, UGA, UAA. (ii) The enzyme that lays an RNA primer in DNA replication/ (iii) The enzyme that makes a double stranded DNA from a single strand RNA template in viral replication (iv) Translocase in protein biosynthesis is also referred to as (v) A compound that inhibits transcription (vi) Name three post-transcriptional modifications in eukaryotes: (viii) Name two types of post-translational modifications on OH containing amino acid proteins: 5. Urea cycle begin inside mitochondria where carbamoyl Phosphate donate its carbamoyl group to ornithine to form . The reaction is catalyzed by , and the product passes form the to the . The second amino group then enters the cycle by a condensation reaction between the amino groups of and ureido group of citrulline, forming in a reaction catalyzed by the product is then cleaved by the enzyme to form fumarate and . In the last reaction of the urea cycle, the cytosolic enzyme cleaves to yield urea and ornithine. 6. Using the active site concept and substrate binding concept, fill the mis