Question

6) Explain what would happen if someone took the drug DNP (dinitrolphenol). DNP allows H+ ions to flow down the concentration gradient and across the inner mitochondrial membrane without going through the ATP Synthase. Why would this be a problem for Cell Respiration? You may want to refer to your diagram of the ETC to help you. Answer this in 3-5 well crafted sentences. 7) Describe what happens to the free energy of the carbon molecules through Cell Respiration. Your answer should include whether the carbon molecules start as low or high energy, what changes their energy and where those carbon atoms wind up at the end of Cell Respiration. Include glycolysis, pyruvate oxidation, and the TCA/Citric Acid Cycle in your discussion. You can choose to answer only with text, an energy diagram graph (like in question #1), or a combination.

Answer 1

1. We know that the energy in the food is converted into the chemical energy of the ATP by the action of electron transport chain present in the inner mitochondrial membrane. The food components (monosaccharides (glucose), fatty acids (acetyl CoA) and amino acid skeleton) are metabolised into carbon dioxide and reductive equivalents (FADH2, NADH +H) in the Kreb’s cycle. The resultant reductive potentials donate their electron to electron transport chain; where the energy released by the travel of the electron downhill through the protein complexes is converted to transport the protons against their concentration gradient towards one side of the mitochondrial membrane. Thus, created electrochemical gradient is utilized by ATPase complex to synthesise ATP from ADP and Pi. The electrons transported by the ETC are finally accepted by O to form H2O.

Ø DNP (stands for 2-4 Dinitro phenol) is lipophilic, and a phenolic compound with ability to bind to the protons.

Ø This DNP binds to the protons and pass across the mitochondrial membrane easily, thus disrupting (or can say uncoupling) the electrochemical gradient of the protons across the mitochondrial membrane.

Ø Due to loss of the proton gradient ATPase cannot synthesise the ATP.

Ø DNP can also inhibit the ETC complexes for the travel of electrons leading to inhibition of cell respiration (due to decreased utilization of oxygen and reduced citric acid or Kreb’s cycle).

2. The free energy is the amount of the energy in the molecules available to do work. Gibbs free energy is the energy available in the molecule to perform work at constant temperature and pressure. Biological systems (living organisms) have highly regulated temperature and pressure, hence obeys propositions of the Gibbs free energy changes in the system.

In the biological systems, biomolecules (especially carbohydrates and fats) are catabolized into carbon dioxide and water and during their catabolism the free energy stored in them is utilized to synthesize ATP, the energy currency of the cell.

Glucose and fatty acids are energetic molecules since the energy is stored in them in the form of chemical bonds. These energy rich molecules are broken down gradually to convert their free energy into reductive potential of molecules viz., NADH, NADPH, and FADH2.

Glucose will get converted to two molecules of pyruvate in a stepwise process called glycolysis. During the process some of the energy is utilized to synthesize 2 molecules each of ATP and NADH. The pyruvate is converted to acetyl CoA and enters the Kreb’s cycle where all the carbon atoms are oxidised into carbon dioxide and all the hydrogens are used up in synthesizing the NADH, FADH2.

Fatty acid also enters the Kreb’s Cycle in the form of Acetyl-CoA and in the process all the carbon atoms are completely oxidised to CO2.

Thus, in the cell respiration, all the energy stored in the reduced form of carbon is captured and in the process the carbon atoms are converted into more oxidised and less energy form.