Chapter 4 | Metabolism and Cellular Respiration

  1. Figure 4.9 Look at each of the processes shown, and decide if it is endergonic or exergonic. In each case, does enthalpy increase or decrease, and does entropy increase or decrease?
    There are four photos show. The first photo shows a pile of wood chips and dirt, with small plants growing from this. The second photo shows a small baby bird breaking out of its egg as it hatches. The third photo shows a large patch of desert where someone has drawn patterns in the sand. The fourth photo shows a grassy hill outside where people climb into giant inflatable balls and roll down the hillside.
    Figure 4.9 Shown are some examples of endergonic processes (ones that require energy) and exergonic processes (ones that release energy). These include (a) a compost pile decomposing, (b) a chick hatching from a fertilized egg, (c) sand art being destroyed, and (d) a ball rolling down a hill. (credit a: modification of work by Natalie Maynor; credit b: modification of work by USDA; credit c: modification of work by “Athlex”/Flickr; credit d: modification of work by Harry Malsch)
  2. Figure 4.11 If no activation energy were required to break down sucrose (table sugar), would you be able to store it in a sugar bowl?
    This plot shows the activation energy for an exergonic reaction. As the reaction proceeds, energy initially increases to overcome the activation energy. In a catalyzed reaction, the activation energy is much lower. The energy then decreases such that the Gibbs free energy of the products is less than that of the reactants. The activation energy is the peak of the energy plot minus the energy of the reactants. The Gibbs free energy is the energy of the products minus the energy of the reactants.
    Figure 4.11 Activation energy is the energy required for a reaction to proceed, and it is lower if the reaction is catalyzed. This diagram’s horizontal axis describes the sequence of events in time.
  3. Figure 4.15 The hydrolysis of one ATP molecule releases 7.3 kcal/mol of energy (∆G = −7.3 kcal/mol of energy). If it takes 2.1 kcal/mol of energy to move one Na+ across the membrane (∆G = +2.1 kcal/mol of energy), how many sodium ions could be moved by the hydrolysis of one ATP molecule?
    This illustration shows the sodium-potassium pump embedded in the cell membrane. A T P hydrolysis catalyzes a conformational change in the pump that allows sodium ions to move from the cytoplasmic side to the extracellular side of the membrane, and potassium ions to move from the extracellular side to the cytoplasmic side of the membrane as well.
    Figure 6.14 The sodium-potassium pump is an example of energy coupling. The energy derived from exergonic ATP hydrolysis pumps sodium and potassium ions across the cell membrane.
  4. Figure 4.25 Dinitrophenol (DNP) is an uncoupler that makes the inner mitochondrial membrane leaky to protons. It was used until 1938 as a weight-loss drug. What effect would you expect DNP to have on the change in pH across the inner mitochondrial membrane? Why do you think this might be an effective weight-loss drug?
    This illustration shows an ATP synthase enzyme embedded in the inner mitochondrial membrane. ATP synthase allows protons to move from an area of high concentration in the intermembrane space to an area of low concentration in the mitochondrial matrix. The energy derived from this exergonic process is used to synthesize ATP from ADP and inorganic phosphate.
    Figure 4.25 ATP synthase is a complex, molecular machine that uses a proton (H+) gradient to form ATP from ADP and inorganic phosphate (Pi). (Credit: modification of work by Klaus Hoffmeier)

     

  5. Figure 4.26 Cyanide inhibits cytochrome c oxidase, a component of the electron transport chain. If cyanide poisoning occurs, would you expect the pH of the intermembrane space to increase or decrease? What effect would cyanide have on ATP synthesis?
    This illustration shows the electron transport chain, the ATP synthase enzyme embedded in the inner mitochondrial membrane, and the citric acid cycle occurring in the mitochondrial matrix. The citric acid cycle feeds NADH and FADH_{2} to the electron transport chain. The electron transport chain oxidizes these substrates and, in the process, pumps protons into the intermembrane space. ATP synthase allows protons to leak back into the matrix and synthesizes ATP.
    Figure 4.26 In oxidative phosphorylation, the pH gradient formed by the electron transport chain is used by ATP synthase to form ATP.
  6. Figure 4.28 Tremetol, a metabolic poison found in the white snake root plant, prevents the metabolism of lactate. When cows eat this plant, it is concentrated in the milk they produce. Humans who consume the milk become ill. Symptoms of this disease, which include vomiting, abdominal pain, and tremors, become worse after exercise. Why do you think this is the case?
    This illustration shows that during glycolysis, glucose is broken down into two pyruvate molecules and, in the process, two NADH are formed from NAD^{+}. During lactic acid fermentation, the two pyruvate molecules are converted into lactate, and NADH is recycled back into NAD^{+}.
    Figure 4.28 Lactic acid fermentation is common in muscle cells that have run out of oxygen.

License

Icon for the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License

Human Biology Copyright © by Janet Wang-Lee is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.

Share This Book