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When the protein gramicidin is integrated into a membrane, an H+

channel forms and the membrane becomes very permeable to protons ( H+
ions). If gramicidin is added to an actively respiring muscle cell, how would it affect the various processes involved in cellular respiration and oxidative phosphorylation? (Assume that gramicidin does not affect the production of NADH
and FADH2
during the early stages of cellular respiration.)
Sort the labels into the correct bin according to the effect that gramicidin would have on each process.
View Available Hint(s)for Part D
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remains the samedroppable
decreases (or goes to zero)droppable
increasesdroppable

1 answer

To understand how gramicidin affects cellular respiration and oxidative phosphorylation, we will consider its specific effect on the proton gradient across the inner mitochondrial membrane. Gramicidin acts as a proton channel, allowing protons (H+) to flow freely across the membrane.

Effects on Processes Involved in Cellular Respiration and Oxidative Phosphorylation:

  1. Proton Gradient Generation

    • Effect: Decreases (or goes to zero)
    • Explanation: Gramicidin allows protons to flow back into the mitochondrial matrix, dissipating the proton gradient that is normally generated by the electron transport chain during oxidative phosphorylation.

  2. ATP Synthesis

    • Effect: Decreases (or goes to zero)
    • Explanation: The proton gradient is necessary for ATP synthase to produce ATP from ADP and inorganic phosphate (Pi). If the gradient is dissipated due to gramicidin, ATP synthesis will significantly decrease or stop.

  3. Electron Transport Chain Activity

    • Effect: Decreases (or goes to zero)
    • Explanation: As protons leak back into the matrix, the electron transport chain will slow down due to a lack of proton gradient, which is necessary for driving the chain complexes. This can lead to a decrease in the overall activity and efficiency of the chain.

  4. NADH and FADH2 Oxidation

    • Effect: Decreases (or goes to zero)
    • Explanation: The oxidation of NADH and FADH2 depends on the ability of the electron transport chain to establish a proton gradient. If the gradient is compromised, the oxidation of these electron carriers will also be negatively affected.

  5. Oxygen Consumption

    • Effect: Decreases
    • Explanation: The electron transport chain requires molecular oxygen as the final electron acceptor. If the flow of protons is disrupted, less NADH and FADH2 are oxidized, leading to decreased oxygen consumption.

Summary of Effects:

  • Proton Gradient Generation: Decreases (or goes to zero)
  • ATP Synthesis: Decreases (or goes to zero)
  • Electron Transport Chain Activity: Decreases (or goes to zero)
  • NADH and FADH2 Oxidation: Decreases (or goes to zero)
  • Oxygen Consumption: Decreases

Correct Bins:

Remains the same:

  • None

Decreases (or goes to zero):

  • Proton Gradient Generation
  • ATP Synthesis
  • Electron Transport Chain Activity
  • NADH and FADH2 Oxidation
  • Oxygen Consumption

Increases:

  • None

By disrupting the proton gradient and reducing the ability to produce ATP through oxidative phosphorylation, gramicidin can severely impair cellular respiration in actively respiring muscle cells.