Active transport mechanisms, or pumps, work against electrochemical gradients. This energy comes from ATP generated through the cell’s metabolism. To move substances against a concentration or electrochemical gradient, the cell must use energy. Department of Biology, Texas A&M University. ![]() This gradient allows for cotransport/secondary transport of sucrose against its concentration gradient as protons come down their concentration gradient via their membrane cotransporter protein. The proton pump creates an electrochemical gradient of protons (hydrogen ions, H+) using ATP to drive primary active transport. We call the combined concentration gradient and electrical charge that affects an ion its electrochemical gradient.įigure 5.17 Proton Gradient provides energy for a secondary active transporter. The electrical gradient of K +, a positive ion, also drives it into the cell, but the concentration gradient of K + drives K + out of the cell ( Figure 5.16). However, the situation is more complex for other elements such as potassium. Thus in a living cell, the concentration gradient of Na + tends to drive it into the cell, and its electrical gradient (a positive ion) also drives it inward to the negatively charged interior. The interior of living cells is electrically negative with respect to the extracellular fluid in which they are bathed, and at the same time, cells have higher concentrations of potassium (K +) and lower concentrations of sodium (Na +) than the extracellular fluid. Because ions move into and out of cells and because cells contain proteins that do not move across the membrane and are mostly negatively charged, there is also an electrical gradient, a difference of charge, across the plasma membrane. ![]() We have discussed simple concentration gradients-a substance's differential concentrations across a space or a membrane-but in living systems, gradients are more complex. Other mechanisms transport much larger molecules. Some active transport mechanisms move small-molecular weight materials, such as ions, through the membrane. If a substance must move into the cell against its concentration gradient-that is, if the substance's concentration inside the cell is greater than its concentration in the extracellular fluid (and vice versa)-the cell must use energy to move the substance.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |