Chemistry 130A - Fall 1993 - Tinoco - Midterm 1

Chemistry 130A- - FRI 17:29 FAX 6434330 MOFFITT LIBRARY 001 Name Chemistry 130A Midterm 1 50 minute open book exam Read the whole test then do the

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Unformatted text preview: 11/24/2000 FRI 17:29 FAX 6434330 MOFFITT LIBRARY 001 Name Chemistry 130A - Midterm 1 50 minute open book exam September 27, 1993 Read the whole test, then do the easiest parts first. 1. (25 points) 7 During exercise glyCOgen~—a polysaccharide—is hydrolyzed to produce glucose (Cd-11205) which is convened to pyruvate by a series of enzyme-catalyzed reactions. The pyruvate is then oxidized to C02 and H20 by steps in the citric acid cycle. The net reaction can be approximated by C6H1206 (S) + 6 02 (g) —> 6 C02 (9+ 6 H20 (1) a. Use the Tables-in the book to calculate AHO for this reaction at 25 °C, 1 atm. b. Use the Tables in the book to calculate A80 for this reaction at 25 DC, 1 arm. c. Calculate AGO for this reaction at 37 “C, 1 atm. You may assume that AH0 and A80 are independent of temperature. (1. In the body the reaction does not occur with solid glucose reacting with 1 arm of 02 gas to form 1 atm of C02 gas and pure water. The main difference in the body is that the glucose is in very dilute solution. Will the free energy for the reaction under these conditions be greater or less than your answer in part (b)? Explain in a few sentences or equations or both. e. The answers to (a) and (b) are in kjoules, but we usually think of food energy in terms of kcal. The glycogen in our bodies came from eating, of course. If all the energy in a teaspoon of sugar (15 kcal) could be converted into work by our muscles, how many times could we lift a weight of 1 pound (mass = 0.454 kg) by llfoot (distance = 0.305 m). 11/24/2000 FRI 17:29 FAX 6434330 MOFFITT LIBRARY 002 Name 2. (25 points) The isomerization of 3—phosphoglycerate to 2-phosphog1ycerate is an important step in the metabolism of glucose. 3—PG ——) 2-PG At pH 7, 25 ‘C its equilibrium constant is K = 0.156. a. What is the standard fiee energy for the reaction (1d) at 25 “C? b. ‘Nhat is the free energy change (kJ) of the reaction when both concentrations are equilibrium concentrations at 25 °C? c. What is the free energy change (ij of the reaction when the concentration of 3—PG = the concentration of 2-PG? d. In a certain cell the concentration of 3—PG = 5.3 X 10‘5 M. Calculate the maximum concentration of 2-PG which will allow the reaction to occur. e. Write the equation you would use to calculate AHO for the reaction from equilibrium constants. If K increases with increasing temperature, what is the sign of AHO? Is heat given off or absorbed by the reaction? 11/24/2000 FRI 17:30 FAX 6434330 MOFFITT LIBRARY 003 _ Name 3. (25 points) You want to estimate the concentration of a probe necessary to find the sequence 5'—GGCT—3' in a target DNA molecule. Use the nearest-neighbor values in the handout sheet to calculate thermodynamic data for the formation of a DNA double strand at 25 °C from the probe 5'- AGCC—B' and the DNA molecule. You can ignore the effect of the dangling ends—the NNN. 5'._.NNNGGCTNNNM3' 5'...NNNGGCTNNN...3' + o o o o (2.) Calculate AGO at 25 “C. (b) Calculate the equilibrium constant K at 25 "C. (c) Write a mass balance equation for the target DNA in terms of concentration of free DNA at equilibrium [DNA], complex concentration [complex], and total DNA [DNAo]. Write a mass balance equation for the probe molecule in terms of [probe], [complex], [probeo]. (d) Using K from part ( b) calculate the concentration of probe necessary to bind 1/2 of the DNA 5' -GGCT—3' sites. The concentration of the probe is much larger than the concentration of the DNA sites. This means that the c0ncentration of probe added to the solution is equal to the free concentration of probe at equilibrium (e) What if the DNA molecule had the probe sequence 5'-AGCC-3' somewhere else in its sequence? Would this increase or decrease the concentration of added probe necessary to bind half the target sequence? Explain qualitatively. ' 11/24/2000 FRI 17:30 FAX 6434330 MOFFITT LIBRARY 004 Name 4. (25 points) (a) Calculate the change in entropy (J K4) for a new deck of 10 cards which is shuffled thoroughly. Its initial state is ordered (1, 2, ...9, 10); its final state is disordered. (b) Calculate the change in entropy (J K4) when 0.80 mol of N2 (gas) is mixed with 0.20 mol of 02 (gas) to make 1 mol of air. (c) A spontaneous reaction occurs at constant temperature and pressure. For each thermodynamic variable (AS,,AH, AG, AE) state whether its sign'is positive, negative, zero, or impossible to tell. (d) Christian Anfinsen received the Nobel Prize for showing that an enzyme (fibonucleasw RNAase) could be completely denatured—unfolded, and then refolded to regain the same active enzyme. The reaction was done at 1 atm pressure: active RNAase (pH 7, 25 “C) —> denatured (8 M urea, 90 °C) —eactive RNAase (pH 7, 25°C) Calculate AS, AH, AG, AE for the complete reaction as written. (e) The statement "You can't unscramble an omelette to make an egg." is a qualitative description of the second law of thermodynamics. Yet you can feed the omelette to a hen and have her metabolically convert the omelette into an egg. Does this mean that hens are not limited by the second law? Answer yes or no and give a one sentence explanation. ...
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This note was uploaded on 05/17/2009 for the course CHEM 130A taught by Professor Kuriyan during the Spring '08 term at University of California, Berkeley.

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Chemistry 130A- - FRI 17:29 FAX 6434330 MOFFITT LIBRARY 001 Name Chemistry 130A Midterm 1 50 minute open book exam Read the whole test then do the

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