Active Transport Quiz

PDF page 221: If a substance must move into the cell against its concentration gradient, the cell must use free energy, often provided by ATP, and carrier proteins acting as pumps to move the substance. Substances that move across membranes by this

PDF page 223: To move substances against a concentration or electrochemical gradient, the cell must use energy. This energy is harvested from ATP generated through the cell’s metabolism. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. Small substances constantly pass through plasma membranes. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements. Much of a cell’s supply of metabolic energy may be spent maintaining these processes. (Most of a red blood cell’s metabolic energy is used to maintain the imbalance between exterior and interior sodium and potassium levels required by the cell.) Because active transport mechanisms depend on a cell’s metabolism for energy, they are sensitive to many metabolic poisons that interfere with the supply of ATP. Two mechanisms exist for the transport of small-molecular weight material and small molecules. Primary active transport moves ions across a membrane and creates a difference in charge across that membrane, which is directly dependent on ATP. Secondary active transport describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP.

PDF page 221: mechanism, a process called active transport, include ions, such as Na and K . The combined gradients that affect movement of an ion are its concentration gradient and its electrical gradient (the difference in charge across the membrane); together these gradients are called the electrochemical gradient. To move substances against an electrochemical gradient

PDF page 222: gradient of K , a positive ion, also tends to drive it into the cell, but the concentration gradient of K tends to drive K out of the cell (Figure 5.16). The combined gradient of concentration and electrical charge that affects an ion is called its electrochemical gradient.

PDF page 222: requires free energy. The sodium-potassium pump, which maintains electrochemical gradients across the membranes of

PDF page 222: nerve cells in animals, is an example of primary active transport. The formation of H gradients by secondary active transport (co-transport) is important in cellular respiration and photosynthesis and moving glucose into cells. Information presented and the examples highlighted in the section support concepts and learning objectives outlined in Big

PDF page 223: To move substances against a concentration or electrochemical gradient, the cell must use energy. This energy is harvested from ATP generated through the cell’s metabolism. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. Small substances constantly pass through plasma membranes. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements. Much of a cell’s supply of metabolic energy may be spent maintaining these processes. (Most of a red blood cell’s metabolic energy is used to maintain the imbalance between exterior and interior sodium and potassium levels required by the cell.) Because active transport mechanisms depend on a cell’s metabolism for energy, they are sensitive to many metabolic poisons that interfere with the supply of ATP. Two mechanisms exist for the transport of small-molecular weight material and small molecules. Primary active transport moves ions across a membrane and creates a difference in charge across that membrane, which is directly dependent on ATP. Secondary active transport describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP.

PDF page 222: We have discussed simple concentration gradients—differential concentrations of a substance across a space or a membrane—but in living systems, gradients are more complex. 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. The interior of living cells is electrically negative with respect

PDF page 222: of Na tends to drive it into the cell, and the electrical gradient of Na (a positive ion) also tends to drive it inward to the negatively charged interior. The situation is more complex, however, for other elements such as potassium. The electrical

PDF page 222: to the extracellular fluid in which they are bathed, and at the same time, cells have higher concentrations of potassium (K )

PDF page 222: and lower concentrations of sodium (Na ) than does the extracellular fluid. So in a living cell, the concentration gradient

PDF page 223: To move substances against a concentration or electrochemical gradient, the cell must use energy. This energy is harvested from ATP generated through the cell’s metabolism. Active transport mechanisms, collectively called pumps, work against electrochemical gradients. Small substances constantly pass through plasma membranes. Active transport maintains concentrations of ions and other substances needed by living cells in the face of these passive movements. Much of a cell’s supply of metabolic energy may be spent maintaining these processes. (Most of a red blood cell’s metabolic energy is used to maintain the imbalance between exterior and interior sodium and potassium levels required by the cell.) Because active transport mechanisms depend on a cell’s metabolism for energy, they are sensitive to many metabolic poisons that interfere with the supply of ATP. Two mechanisms exist for the transport of small-molecular weight material and small molecules. Primary active transport moves ions across a membrane and creates a difference in charge across that membrane, which is directly dependent on ATP. Secondary active transport describes the movement of material that is due to the electrochemical gradient established by primary active transport that does not directly require ATP.

PDF page 222: nerve cells in animals, is an example of primary active transport. The formation of H gradients by secondary active transport (co-transport) is important in cellular respiration and photosynthesis and moving glucose into cells. Information presented and the examples highlighted in the section support concepts and learning objectives outlined in Big

PDF page 224: An important membrane adaption for active transport is the presence of specific carrier proteins or pumps to facilitate movement: there are three types of these proteins or transporters (Figure 5.17). A uniporter carries one specific ion or molecule. A symporter carries two different ions or molecules, both in the same direction. An antiporter also carries two different ions or molecules, but in different directions. All of these transporters can also transport small, uncharged organic molecules like glucose. These three types of carrier proteins are also found in facilitated diffusion, but they do not require

PDF page 224: An important membrane adaption for active transport is the presence of specific carrier proteins or pumps to facilitate movement: there are three types of these proteins or transporters (Figure 5.17). A uniporter carries one specific ion or molecule. A symporter carries two different ions or molecules, both in the same direction. An antiporter also carries two different ions or molecules, but in different directions. All of these transporters can also transport small, uncharged organic molecules like glucose. These three types of carrier proteins are also found in facilitated diffusion, but they do not require

PDF page 224: An important membrane adaption for active transport is the presence of specific carrier proteins or pumps to facilitate movement: there are three types of these proteins or transporters (Figure 5.17). A uniporter carries one specific ion or molecule. A symporter carries two different ions or molecules, both in the same direction. An antiporter also carries two different ions or molecules, but in different directions. All of these transporters can also transport small, uncharged organic molecules like glucose. These three types of carrier proteins are also found in facilitated diffusion, but they do not require

PDF page 224: same direction. An antiporter also carries two different molecules or ions, but in different directions. (credit: modification of work by “Lupask”/Wikimedia Commons)

PDF page 224: ATP to work in that process. Some examples of pumps for active transport are Na -K ATPase, which carries sodium and

PDF page 224: potassium ions, and H -K ATPase, which carries hydrogen and potassium ions. Both of these are antiporter carrier proteins.

PDF page 225: sodium-potassium pump moves K into the cell while moving Na out at the same time, at a ratio of three

PDF page 225: Na for every two K ions moved in. The Na -K ATPase exists in two forms, depending on its orientation to the interior or exterior of the cell and its affinity for either sodium or potassium ions. The process consists of the following six steps: