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  1. Phosphoglucose isomerase catalyzes the interconversion of glucose 6-­‐‑phosphate (G6P) and fructose 6-­‐‑phosphate (F6P):
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    a. At equilibrium, the ratio of [F6P] to [G6P] is observed to be 0.5. What are the values of ΔG and ΔG°?
    b. Inside a cell, the reaction is not at equilibrium. The value of ΔG in cellular conditions is measured as –2.51 kJ/mol. What is the ratio of [F6P] to [G6P] inside the cell?
  2. Normal differentiated cells that are no longer actively growing rely primarily upon aerobic respiration to generate ATP, except when they experience decreased levels of oxygen, in which case they switch to glycolysis. In contrast, cancer cells rely heavily upon glycolysis for producing ATP, regardless of the presence of oxygen. Cancer cells can increase the rate of glycolysis up to 200-­‐‑fold compared to normal cells. Cancer cells undergo rapid unrestrained proliferation. The increased reliance of cancer cells upon glycolysis therefore seems paradoxical, since glycolysis generates far less ATP from each glucose than does oxidative respiration. Can you come up with any reason(s) why glycolysis may be advantageous to rapidly proliferating cancer cells?
  3. Would the following regulatory schemes make sense to you or not?
    1. Pyruvate kinase is inhibited by high concentrations of ATP.
    2. Phosphofructokinase is inhibited by low concentrations of citrate.
    3. Phosphofructokinase is activated by high concentrations of ADP.
    4. The enzyme that converts isocitrate to a-­‐‑ketoglutarate is activated by low concentrations of ADP.

6. Integrating Question 14 (section 10.2 of your textbook) asks you to investigate four different lipid metabolism diseases found in humans. Based on what you learn from this investigation, how important is it that humans are able to metabolize fatty acids to 2-­‐‑carbon products?

5. Given that fatty acids are fully oxidized once they enter the mitochondria, where is the logical place for regulation of beta oxidation? Speculate what molecule could function as a regulator of beta oxidation. (Note: this is Integrating Question 17 from section 10.2 of your textbook)

14-Search OMIM for these ID numbers that are associated with genetic diseases related to lipid digestion: 201450, 609016, 201470, and 201475. What can you deduce about beta oxidation based on the OMIM results? Are there serious consequences for the inability to convert fatty acids into 2-carbon molecules?

  1. Integrating Question 26 (section 10.2) in your textbook asks you to use data in figure 10.15 to determine which steps of glycolysis might be reasonable targets for regulation. This is based on measured values of the concentrations of intermediates in the pathway. Another approach to predicting regulation arises from considering the DGs of the individual reactions. These values are provided on the glycolysis “cheat sheet” you were given.
    Can you find any correlation between the DG values for each reaction and the concentration of intermediates? Why it is reasonable to identify potential regulatory steps based on the DGs of those reactions?

26. How many of the enzyme steps in glycolysis are limited by substrate (intermediates 2 to 7) availability? How many are regulated by the rate of the enzyme? If you were going to regulate the rate of acetyl-CoA production (final product 8) from glucose (substrate 1), which enzymatic step would you modulate? Explain your answer using the data in Table 10.15.

7.In actively respiring liver mitochondria, the pH inside the matrix is about one pH unit higher than that in the cytosol.

  1. Assuming that the cytosol is at pH 7.5 and the matrix is a sphere with a diameter of 1 μM, calculate the total number of protons in the matrix of a respiring liver mitochondrion.
  2. If the matrix began at pH 7.5 (equal to that in the cytosol), how many protons would have to be pumped out to establish a matrix pH of 8.5?
  3. The electrochemical proton gradient is responsible not only for ATP production in bacteria, mitochondria, and chloroplasts, but also for powering bacterial flagella. The flagellar motor is thought to be driven directly by the flux of protons through it. To test this idea, you analyze a motile strain of Streptococcus. These bacteria swim when glucose is available for oxidation, but they do not swim when glucose is absent (and no other substrate is available for oxidation).
    1. Ionophores are compounds that allow specific ions to freely cross a membrane. Using a series of ionophores that alter the pH gradient or the membrane potential, you make several observations. Are each of the four observations below consistent with the proposed model (that is, that flagellar motion is driven by an influx of protons through the flagellar motor)? Why or why not? Note that in these experimental conditions, the [K+] inside the bacterial cells is lower than the [K+] that is present in the growth medium outside the cells.
      i. Bacteria that are swimming in the presence of glucose stop swimming upon addition of the proton ionophore FCCP.
      ii. Bacteria that are swimming in the presence of glucose in a medium containing K+ are unaffected by the addition of the K+ ionophore valinomycin.
      iii. Bacteria that are motionless in the absence of glucose in a medium containing K+ remain motionless upon addition of valinomycin.
      iv. Bacteria that are motionless in the absence of glucose in a medium containing Na+ swim briefly upon addition of valinomycin and then stop.
    2. Normal bacteria can swim in the presence or absence of oxygen. However, mutant bacteria that are missing ATP synthase, which couples proton flow to ATP production, can swim only in the presence of oxygen. How are normal bacteria able to swim in the absence of oxygen when there is no electron flow?
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    • 15.11.2019

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