Biochemistry Mid-Semester Exam — 2016 (Past OmpathStudy

Biochemistry Mid-Semester Exam — 2016 (Past Paper) University of Nairobi Level 1 Biochemistry mid-semester exam, 2016. Full text transcription of the original scanned paper — questions only. --- " MARKING SCHEME " Other names Reg. No. Group UNIVERSITY OF NAIROBI DEPARTMENT OF BIOCHEMISTRY MID OF SECOND SEMESTER CONTINUOUS ASSESSMENT TEST FOR LEVEL - I MBCHB, BPHARM & BDS (2016/2017) DATE: Wednesday, May 4 2016 TIME: 2.00 – 5.00 PM SECTION A (30Marks) : Answer ALL questions in the spaces provided 1. Write the two half reactions (i and ii) and the overall equation (iii) for:- (a) Aerobic glycolysis (i) Glucose $\longrightarrow$ 2 Pyruvate$^-$ + 2 H$^+$ (ii) 2 ADP + 2 Pi + 2 NAD$^+$ + 4 ADP $\longrightarrow$ 4 ATP + 2 H$ 2$O + 2 NADH + 2 H$^+$ + 2 ADP (iii) Glucose + 2 ADP + 2 Pi + 2 NAD$^+$ $\longrightarrow$ 2 Pyruvate + 2 H$^+$ + 2 NADH + 2 H$^+$ + 2 ATP + 2 H$ 2$O (b) Anaerobic glycolysis (i) Glucose $\longrightarrow$ 2 Lactate$^-$ + 2 H$^+$ (ii) 2 ADP + 2 Pi + 2 NAD$^+$ + 2 NADH + 2 H$^+$ + 4 ADP $\longrightarrow$ 4 ATP + 2 H$ 2$O + 2 NADH + 2 H$^+$ + 2 NAD$^+$ + 2 ADP (iii) Glucose + 2 ADP + 2 Pi $\longrightarrow$ 2 Lactate$^-$ + 2 H$^+$ + 2 ATP + 2 H$ 2$O (c) Explain why the two equations (a iii and b iii, above) are different. In aerobic glycolysis, the two molecules of NADH made in the cytosol are reoxidized to $\text{NAD}^+$ by transfer of their electrons to the ETC in the mitochondria. The electrons are used to reduce $\text{O} 2$ to water $2\text{NADH} + 2\text{H}^+ + \text{O} 2 \longrightarrow 2\text{NAD}^+ + 2\text{H} 2\text{O}$ In anaerobic glycolysis, the two NADH are reused by the LDH to generate $2\text{NAD}^+$ that are reused by the G3P-DH to keep glycolysis going. (d) If the sum $\Delta\text{G}^{01}$ for conversion of glucose to lactate is - 47 kcal/mol, calculate the overall $\Delta\text{G}^{01}$ for anaerobic glycolysis in an active muscle. $-47 + (+14.6) = -32\text{ kcal/mol}.$ Input of ATP in the investment phase of glycolysis. $2\text{ADP} + 2\text{Pi} \longrightarrow 2\text{ATP} + 2\text{H} 2\text{O} \quad +14.6\text{ kcal/mol} = \Delta\text{G}^{01}$ 2. In the liver, heart and kidney, the NADH - dehydrogenase (E-FMN) of the inner mitochondrial membrane (IMM) accept electrons only from mitochondrial NADH. How, then, is cytosolic NADH (arising from the reaction of G3P-dehydrogenase) able to cross the IMM under aerobic conditions? <u NB: Use a scheme to answer the question.</u "MARKING SCHEME" 3. With full details, describe:- a) A substrate -level phosphorylation reaction involving a diphosphate-containing substrate. (2) 1, 3-Bisphosphoglycerate = 3-Phosphoglyceroyl phosphate (2) 3-Phosphoglycerate b) An anaplerotic reaction that requires biotin Pyruvate Oxaloacetate (OAA) c) A condensation reaction. Acetyl CoA OAA Citrate "MARKING SCHEME" SECTION B (30 Marks): Answer all questions in the spaces provided 1. Fill-in the missing details:- When $\text{k}^1\text{eq}$ is; $\Delta\text{G}^{01}$ is; Reaction proceeds; --- --- --- 6.8 $\approx -1.14 \text{ kcal/mol}$ Forward (to the right) 0.0475 $\approx +1.82$ In Reverse (to the left) 254 $\approx -3.28$ N/A IGNORE $\approx 263$ -3.3kcal/mol Forward $\approx 0.28$ +0.75 In Reverse $\approx 30.3$ -2.02 2. An $\text{H}^+$ transporting ATPase located in the plasma membrane of the parietal cells actively pumps $\text{H}^+$ into the stomach lumen. If the actual $[\text{H}^+]$ in the cells is $10^{-7}\text{M}$ while that in the stomach is $0.1\text{M}$, calculate the actual change in free energy required to transport 1 mole of $\text{H}^+$ ion into the stomach of a human. $$\Delta \text{G} = 2.303 \text{ RT} \log \frac{c 2}{c 1}$$ $$\Delta \text{G} = 2.303 \times 1.987 \times 310 \times \left(\log \frac{[0.1]}{[10^{-7}]}\right) = 6$$ $$\Delta \text{G} = 2.303 \times 1.987 \times 310 \times 6$$ $$\Delta \text{G} = 8511.473 \text{ cal/mol}$$ $$\Delta \text{G} = 8.511 \text{ kcal/mol} = \text{This is the } \overset{\text{amount of}}{\text{energy}} \text{ that}$$ $$\text{is required to transport}$$ $$1 \text{ mol of } \text{H}^+ \text{ across the}$$ $$\text{membrane (against a}$$ $$\text{concentration gradient)}$$ $\underline{\text{NB}}$ Value of $R = 1.987 \text{ cal/mol k}$ $\text{Temperature} = 37^\circ\text{C } (\text{normal body temp.}) = 310\text{ K}$ 3. (a) Name the two main activators and the two main inhibitors of the major regulatory glycolytic enzyme in the muscle. <u Activators</u Fructose 2,6-Biphosphate AMP <u Inhibitors</u ATP Citrate (b) Muscle and liver glycogen phosphorylases are both modulated by ATP, while non-covalently regulated by AMP and Glucose, respectively. (b) The entry of glucose residues into the glycolytic pathway is regulated by two enzymes namely Hexokinase and Glycogen phosphorylase while the glycolytic pathway is primarily regulated by the enzyme PFK-1. 4. (a) List/Name 5 proteins (not complexes) which serve as carriers through which electrons pass to reach molecular oxygen during electron transport in the mitochondria.