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Student ID: Name: Midterm 1 - Version A INSTRUCTIONS: KEEP CALM 1. Please write legibly, clearly and succintly. We grade on what we can read and understand - not what you think you wrote or marked! 2. Please be concise. You will not get more points just for writing more stuff! 3. Please fill out your name and Student ID clearly for the Rapid Return sheet. If you don’t do this, you won’t get your answer script returned to you! AND GET YOUR MIDTERM ON 4. Don’t PANIC! Stressing yourself out has exactly ZERO positive consequences! MULTIPLE CHOICE INSTRUCTIONS: 1. Unclearly marked answers WILL NOT be considered a reason for regrading. 2. Each question will only have ONE TRUE statement, or only ONE correct answer (which you should mark as TRUE). 3. For each choice of each question, mark off ONLY ONE (True/False/Unsure). If you leave a choice blank, it will be counted as “Unsure” If you mark multiple answers for an answer choice, it will be counted as “Unsure” Key: T=TRUE, F=FALSE, ?=UNSURE 4. Scoring: A choice that is TRUE, which is marked as TRUE will get +1 A choice that is FALSE, which is marked as FALSE will get +1 A choice marked as UNSURE will get 0 A choice that is FALSE which is marked as TRUE will get -1 A choice that is TRUE, which is marked as FALSE will get -3 Your score for each question can therefore range from +4 to -3 Student ID: Name: 01. The effect of an enzyme on a chemical reaction is to (select the BEST answer) _______ : T T T T F F F F ? ? ? ? A) B) C) D) decrease the Keq get to the Keq faster increase the Keq change the Keq 02. Select the BEST choice regarding the statement below: Active sites of enzymes cannot have amino acids with hydrophobic R-groups. T F ? A) T F ? B) T F ? C) T F ? D) TRUE: hydrophbic residues will be on the inside of proteins, while active sites are on the outside TRUE: hydrophobic residues will prevent the substrate from binding the active site FALSE: weak interactions with hydrophobic residues can stabilize the transition state FALSE: hydrophobic residues cause water to be excluded from active sites, thereby allowing the substrate to bind 03. The measured activity of 1 mg of a protein in water is 455 units. The measured activity of 1 mg of the same protein in benzene (a non-polar solvent) is 2 units. What is the best explanation for this data? T T F F ? ? A) B) Non-polar solvents disrupt H-bonds required for secondary structure T T F F ? ? C) D) Covalent peptide bonds are broken in non-polar solvents Non-polar solvents disrupt hydrophobic interactions required for tertiary structure H-bonding and hydrophobic interactions are disrupted in non-polar solvents 04. The BEST statement about the data shown in the graph is: F ? A) T F ? B) T F ? C) T F ? D) Solid line is catalyzed reaction because it has lower activation energy Dotted line is catalyzed reaction because [Products] is higher ^ A [Products] T Time (minutes) Solid line is catalyzed reaction because is has a lower slope Dotted line is catalyzed reaction because it reaches equilibrium faster 05. Refer to the point marked “A” in the figure for Question 4. Which statement BEST describes “A”? T T T T F F F F ? ? ? ? A) B) C) D) Reaction equilibrium; no change in [Products] Reaction equilibrium; no change in ∆G Transition state; highest energy of reaction Transition state; extremely short-lived intermediate Student ID: Name: 06. Two enzymes that catalyze different reactions contain the same domain. Which statement BEST applies to this situation? T F ? A) T T T F F F ? ? ? B) C) D) Extremely unlikely. Enzymes with similar domains should catalyze similar reactions The common domain is likely non-functional in these enzymes The two enzymes could have evolved from a common protein The common domain will most likely be mutated in one of the proteins 07. The figure depicts the primary structure of an enzyme. The amino acids that make up the active site are marked for the wild type enzyme (top amino acids) and a mutant enzyme (bottom amino acids). Based on this, what is the BEST prediction? T F ? A) T F ? B) T F ? C) T F ? D) Wild type Mutant Phe Tyr Leu Ala Lys Phe Tyr Ile Ala Lys Mutant enzyme will have lower activity; Ile will not bind substrate as well as Leu, and will not stabilize the transition state Mutant enzyme will have lower activity; mutation will cause protein to unfold Mutant enzyme will have the same activity as wild type; Leu and Ile have similar R-groups with similar weak bonds Mutant enzyme will have higher activity; Ile will accomodate the substrate better and stabilize the transition state better T F ? A) T F ? B) T F ? C) T F ? D) Solid line is mutant enzyme; [Products] is lower Dotted line is mutant enzyme; reaches equilibrium faster Solid line is mutant enzyme; reaches equilibrium slower [Products] 08. The BEST statement about the data shown in the graph is: Time (minutes) Cannot tell which is mutant or wild type; mutations can increase or decrease enzyme activity T T F F ? ? A) B) Only Reaction 1 is spontaneous, Keq > 1 T F ? C) T F ? D) Only reaction 1 is non-spontaneous, ∆G is positive Both Reaction 1 and 2 are spontaneous, Keq is positive Both reaction 1 and 2 are non-spontaneous, ∆G is positive Keq 09. The BEST statement about the data shown in the graph is: 8 7 6 5 4 3 2 1 Reaction 1 Reaction 2 Student ID: Name: 10. What is the BEST explanation for why you cannot lift the same weight as Arnold Schwarzenegger? T T T T F F F F ? ? ? ? A) B) C) D) His muscles have more actin and myosin than you His muscles have more actin, myosin and ATP than you His muscles have more ATP than you He has mutant actin and/or myosin Activation energy = 5 kCal mol-1 11. A -> X + Y ∆G = -29 kCal mol-1; -1 X -> D + E ∆G = +3 kCal mol ; Activation energy = 10 kCal mol-1 We can couple these two reactions to carry out the overall reaction: A -> Y + D + E. Which of the following statements is TRUE about these reactions? T T F F ? ? A) B) A -> X+Y will occur more slowly since its activation energy is lower T F ? C) T F ? D) The coupled reaction will have a very low Keq (<0.5) since its rate is very high The coupled reaction will be very slow since its activation energy will be 15 kCal mol-1 X -> D+E is an endergonic reaction, that might be reversible 12. A -> B + C Activation energy = 10 kCal mol-1 X + C -> Y ∆G = +3 kCal mol-1; A + X -> Y + B ∆G = -13 kCal mol-1; Activation energy = 6 kCal mol-1 Based on the reactions shown, pick the BEST conclusion about reaction A -> B+C T T T T F F F F ? ? ? ? A) B) C) D) Must be faster than either of the other two reactions Must be carried out by an enzyme Must be exergonic, and have a ∆G lower than -15 kCal mol-1 Must be spontaneous 13. For each amino acid shown, in the box below the amino acid, write down the STANDARD THREE LETTER designation for the amino acid. If the molecule shown is a non-standard amino acid, write in “NS.” 0.5 X 4 points + NH3 CH COOCH3 + NH3 CH COO- + NH3 CH COO- + NH3 CH CH2 CH2 CH2 CH2 CH2 COO- CH2 COO- CH2 NH3 + NH3 + Student ID: 14. The reaction A --> B is catalyzed by the enzyme E1, ∆G = 8 kJ mol-1 The reaction B --> C is catalyzed by the enzyme E2. Addition of E1 and E2 to A results in formation of C. You start off with 2 moles of A in 1 L of solution at 298K. You then add either E1 alone (solid line) or E1 and E2 (dashed line) and measure the product formed over time. Your data is shown in the figure. Based on all this, what is the BEST conclusion about the reaction B --> C? Specifically, what would you predict is the ∆G of B --> C? Explain your answer. A + E1 + E2 [Products] Name: A + E1 Time (minutes) 4 points 16. The ∆G for the reaction D --> E is -23 kJ mol-1. I start off with 1 mole of D and measure the amount of E that is produced over time. My data is shown in the graph. Most likely, what did I do at the point marked “X” in the graph? Explain your answer. 3 points [E] 15. A protein is composed only of the amino acids Ala, Gly, Val, Leu, Ile, and Phe. This protein is insoluble in water, and forms large aggregates when placed in pure water. What is the BEST explanation for all this? 3 points X Time (minutes)