In this video, we're going to begin our lesson on how the proton motive force drives prokaryotic flagellar motility. The proton motive force is commonly abbreviated as PMF. The proton motive force or PMF refers to the energy that is generated from the transport of protons or hydrogen ions (H+) across the plasma membrane. This proton motive force is generated via a series of three steps that we have numbered below, 1, 2, and 3. These numbers correspond with the numbers in the image below. Keep that in mind as we go through this.
In the very first step of generating the proton motive force, protons or hydrogen ions are going to be pumped from the periplasm into the cell's cytoplasm. If we take a look at our image below, notice that this is an image of the proton motive force. This process involves the movement of protons across the membrane to generate energy. Also, notice that this image shows the structure of a gram-negative cell's flagellum. You can tell because there is an outer membrane here, which is associated with gram-negative cells. Protons, these H+ ions in the periplasm, are going to be transported and pumped into the cell cytoplasm. You can see that the direction of movement here is in this direction right here.
These protons that are pumped into the cytoplasm are going to interact with charged amino acids on the MS ring protein. Recall that protons are positively charged (H+ ions) and thus are able to interact electrostatically with other charged particles such as amino acids. In step two here, we're showing you the proton and MS ring interaction, electrostatic interaction. You can see the protons interacting with the MS ring, which is right here. Then, the interaction with the MS ring is going to cause the flagellum to rotate. The rotation of the flagellum will lead to either a run or a tumble.
The speed at which the protons are pumped into the cell controls the rotational speed of the flagella. In step number three, we can see how the interaction between the MS ring and the protons leads to flagellar rotation, which consequently moves the flagella. The energy from the proton motive force or PMF is used to move the cell toward a more favorable environment where the cell is more likely to survive and thrive. This ability for cells to move toward more favorable environments is referred to as chemotaxis, which we will talk about in our next lesson video.
For now, this here concludes our brief lesson on how the proton motive force drives prokaryotic flagellar motility. We'll be able to get some practice applying these concepts as we move forward. So, I'll see you in our next video.
