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BCHM 561 exam 1 - BCHM 561 EXAM I Fall 2009 NAME(please...

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- ± - NAME ( please print clearly ) Please write legibly in the space provided. If additional space is needed to write your answers, use the back of the pages provided making sure you include the question number. The total points assigned to each question are enclosed in brackets. There are a total of 200 points. There may be more than one correct selection for multiple choice questions. Circle all correct choices. CONCEPTS FROM CHEMISTRY (Chapter 1) ±. [4] Describe two things that the free-energy change (∆G) can reveal about a biochemical reaction or process. 2. [4] For a chemical or biochemical reaction occurring at constant pressure and volume, the equation for the free-energy change (∆G) contains two terms, the change in enthalpy (∆H) and change in entropy (∆S). Which of these two terms expresses or most closely reflects the number and nature of the chemical bonds and/or noncovalent interactions that are formed and broken during the reaction? 3. [6] ∆H and –T∆S values are given below for four different biochemical reactions. Which of these reactions are thermodynamically favored processes that will occur spontaneously? ( circle the correct answers ) A. ∆H = – 32 kJ/mol – T∆S = – 13 kJ/mol B. ∆H = – 86 kJ/mol – T∆S = + 106 kJ/mol C. ∆H = – 10 kJ/mol – T∆S = + 16 kJ/mol D. ∆H = + 100 kJ/mol – T∆S = + 22 kJ/mol Using the ∆H and –T∆S values given above, can you predict which of the four reactions will occur at the greatest rate? Yes No Based on the ∆H and –T∆S values provided above, which for the four reactions occurs with the greatest increase in the randomness or disorder of the system? A B C D BCHM 561 EXAM I Fall 2009 The enthalpy change is a measure of the change in heat content of the system during a reaction. For chemical reactions, the enthalpy changes approximate the difference in energy used to break bonds and the energy released upon formation of new bonds. In contrast, the change in entropy ( ∆S ) reflects alterations in the extent of randomness or disorder in the system. enthalpy change (∆H) (1) ∆G can be used to determine whether a biochemical reaction will occur spontaneously as written or conceived. ∆G is negative for spontaneous processes. (2) ∆G is a measure of the energy released from a reaction that is available to do work.
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- 2 - 4. [±2] Briefly, define the following terms. A. Hydrogen bonds B. Electrostatic interactions C. Van der Waals interactions D. Hydrophobic interactions 5. [4] List two types of noncovalent interactions that are important in providing stability to the three- dimensional structures of macromolecules. 6. [4] Why is it important that noncovalent interactions, as opposed to covalent bonds have a major role in stabilizing the three-dimensional structure of macromolecules? A hydrogen bond is an electrostatic interaction between a hydrogen atom carrying a partial positive charge (as a result of its bonding to an electronegative atom) and a second atom carrying a partial negative charge (typically a N or O atom).
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