What happens to the protons receIved trom NADH in bacteria?
They are passed along the electron transport chain along with the electrons, setting up a proton motive force.
They act as coenzymes in chemical reactions.
They act as terminal electron acceptors.
They are transported across the cytoplasmic membrane, setting up a proton motive force.
The Correct Answer and Explanation is :
The correct answer is:
They are passed along the electron transport chain along with the electrons, setting up a proton motive force.
Explanation
In bacterial cells, as in many other organisms, NADH is a crucial molecule in cellular respiration, particularly in the process of oxidative phosphorylation. NADH is formed in earlier stages of respiration such as glycolysis and the Krebs cycle. The main role of NADH in the electron transport chain (ETC) is to donate electrons that it carries from these metabolic processes.
Here’s how it works in bacteria:
- NADH Donation: NADH donates the electrons it carries to the first complex of the electron transport chain. This complex is often referred to as NADH dehydrogenase (Complex I).
- Proton Movement: When NADH donates electrons to Complex I, this complex uses some of the energy from these electrons to pump protons (H+) from the cytoplasm to the periplasm or across the inner mitochondrial membrane in eukaryotes. This action establishes a gradient of protons across the membrane, which is crucial for the next step.
- Creating Proton Motive Force: The pumping of protons across the membrane leads to a difference in concentration and charge across the membrane, known as the proton motive force (PMF). This force is essentially a store of potential energy which is then used by ATP synthase.
- ATP Synthesis: The proton motive force drives protons back across the membrane through the enzyme ATP synthase. The flow of protons through ATP synthase provides the energy necessary for the synthesis of ATP from ADP and inorganic phosphate.
The other options given do not describe the role of protons in bacterial electron transport chain correctly:
- Protons acting as coenzymes: Protons (H+) are ions, not coenzymes. They do not participate directly in catalyzing reactions but are involved in creating the proton motive force.
- Protons as terminal electron acceptors: In bacterial respiration, the terminal electron acceptors can vary (e.g., oxygen in aerobic respiration, sulfate in some types of anaerobic respiration) but protons are not electron acceptors. They are the particles being transported to create the PMF.
- Protons transported across the cytoplasmic membrane: While technically true, this choice does not explicitly connect the process to the activity of NADH and the electron transport chain, making it a less accurate answer.