Glycolysis Case Study

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1. If the reaction XA + Y XY + A has a ΔG of +7.3 kcal/mol, could this reaction be driven in the cell by coupling it to ATP hydrolysis? Why or why not? (10 pts)

The ΔG value for ATP hydrolysis is approximately -30 kcal/mol (Milo, R., & Phillips, R. (n.d.)). The reaction could be driven in the cell by coupling it using ATP hydrolysis because the ΔG value of the reaction would be about -22.7 kcal/mol (Ahern, K. (n.d.).). The products (XY+A) can be used as the reactants in another reaction.

2. Using two of the steps in glycolysis, explain how a favorable reaction is linked to an unfavorable reaction to allow the unfavorable reaction to occur. Be specific in your description. Include products and reactants, ΔG values, and whether …show more content…

Step 8 to 9 is also unfavorable because the delta G value is +0.4, but step 9 to 10 has a delta G value of -7.5. These reactions are able to take place because of coupling—the product of one unfavorable reaction is the reactant of a different favorable reaction. According to Le Chatelier's principle, since the product of the unfavorable reactions are always being used as the reactant of a favorable reaction, the unfavorable reaction will always take place because the removal of a product will result is a shift in equilibrium to make more product. The product of step 2, glucose 6-phosphate, is used in the next reaction as a reactant and favorably forms fructose 6-phosphate. Similarly, from steps 8 to 9, 2-phosphoglycerate is used as a recant to form phosphoenolpyruvate. Step 9 still results in a positive delta G, but step 10 (formation of pyruvate) has a delta G value of -7.5. the formation of ATP drives the unfavorable reaction in the forward …show more content…

3. Using a reaction from the citric acid cycle, please explain oxidation and reduction. Be specific in your description. Include products and reactants, which molecules are oxidized and reduced, and what the oxidizing and reducing agents are in reaction. Why must we speak of oxidation and reduction together? (10 points)

In the first step of the citric acid cycle, NAD+ is reduced to NADH. The oxidizing agent is NAD+ because it accepts electrons and NADH is the reducing agent because it is able to give up electrons. In the reverse reaction, NADH is oxidized to form NAD+, so NADH is still the reducing agent and NAD+ is the oxidizing agent. Oxidation and reduction must go together because, for example, when a substance loses electrons, there must be another substance that is able to accept those electrons.

Citation: Slides 6 and 25 from Week 6 lecture

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