Exam 1 Review: Chapter 3 - Active Transport
active transport process - The movement of ions or molecules, e.g., a Na+ ion or a glucose, through a cell membrane, usually along a gradient of concentration or electrical potential in the direction opposite to normal diffusion, requiring the expenditure of energy from ATP hydrolysis; the ATP hydrolysis may occur at the same site as the movement of the ions or molecules through the membrane (primary active transport) or the ATP hydrolysis may occur at a different site from the movement of the ions or molecules through the membrane (secondary active transport ); a variety of membrane-bound proteins have this capacity, e.g., ion pumps, symporters, and antiporters; processes of vesicular transport, i.e., endocytosis and exocytosis are also examples of active transport processes. [Note: It is a general characteristic of living cells that the intracellular concentration of many solutes differs from their concentration in the surrounding solution. Maintenance of this "non-equilibrium" condition requires the input of energy. This energy is used by transport processes which, unlike facilitated diffusion, can move substrates against an electrochemical gradient. The ability of these processes to move substrates in oppsition to their electrochemical gradients resulted in coining the collective term "active" transport to them.]
primary active transport - The movement of ions or molecules, e.g., a Na+ ion or a glucose, through a cell membrane, usually along a gradient of concentration or electrical potential in the direction opposite to normal diffusion, requiring the direct expenditure of energy in which ATP hydrolysis occurs at the same site as the movement of the ions or molecules through the membrane; a variety of membrane-bound proteins have this capacity, e.g., ion pumps, symporters, and antiporters.
secondary active transport - The movement of ions or molecules, e.g., a Na+ ion or a glucose, through a cell membrane, usually along a gradient of concentration or electrical potential in the direction opposite to normal diffusion, requiring the indirect expenditure of energy in which ATP hydrolysis occurs at a different site (often a primary active transport system such as a Na+/K+ ATPase transport system) from the movement of the ions or molecules through the membrane; a variety of membrane-bound proteins have this capacity, e.g., ion pumps, symporters, and antiporters.
Sodium pump = NA+/K+ pump = NA+/K+ ATPase - An integral membrane protein active transport molecule which has the capacity to bind and hydrolyze ATP and use the energy from the ATP hydrolysis to move 3 Na+ ions from the cytoplasm to the exterior of the cell while simultaneously moving 2 K+ ions from the exterior of the cell into the cytoplasm; the action of this ion pump is the main factor in establishing a resting membrane potential for the cell.
symport - A type of active transport protein found in cell membranes which moves two different ions or molecules, e.g., a Na+ ion and a glucose, in the same direction across the membrane; often one ion or molecule can be moved in opposition to its concentration gradient because the movement of the other ion or molecule, moving in accord with its concentration gradient, is driving the process; ultimately, the movement is powered by ATP hydrolysis, but that energy source may be directly (primary active transport) or indirectly (secondary active transport) associated with the active transport protein. aka - symporter.
antiport - A type of active transport protein found in cell membranes which moves two different ions or molecules, e.g., a Na+ ion and a glucose, in opposite directions across the membrane; often one ion or molecule can be moved in opposition to its concentration gradient because the movement of the other ion or molecule, moving in accord with its concentration gradient, is driving the process; ultimately, the movement is powered by ATP hydrolysis, but that energy source may be directly (primary active transport) or indirectly (secondary active transport) associated with the active transport protein.. aka - antiporter.
cotransport - The linked, simultaneous movement of one ion or molecular species across a semipermeable membrane, coupled with the simultaneous movement of another ion or molecular species across the same membrane in the same direction; e.g., the transport of Na+ ions from the area of high to low concentration can provide the necessary energy for the transport of the second species, e.g., glucose or an amino acid, in the same direction but in opposition to the glucose or amino acid concentration gradient; this is the function of symports = symporters.
countertransport - The linked, simultaneous movement of one ion or molecular species across a semipermeable membrane, coupled with the simultaneous movement of another ion or molecular species across the same membrane in the opposite direction; e.g., the transport of Ca++ ions from the area of high to low concentration can provide the necessary energy for the transport of the second species, e.g., H+ ions, in the opposite direction and in opposition to the H+ ion concentration gradient; this is the function of antiports = antiporters.
There is an animation of active transport linked in here. You will need Shockwave Flash software (which may be downloaded from the Internet for free) to view them.
List:
6. two active processes that move substances into and out of cells.
active transport - vesicular transport
7. two types of active transport observed within cell membranes.
primary active transport - secondary active transport
19. the number and direction of sodium and potassium ions which move into and out of cells in one cycle of the Na+/K+ ATPase "sodium-potassium" pump.
3 Na+ ions out & 2 K+ ions in
[The energy from one ATP hydrolysis is used to move 3 Na+ ions from the cytoplasm to the exterior of the cell while simultaneously moving 2 K+ ions from the exterior of the cell into the cytoplasm.]
Sketch and Label:
12. the action of the Na+/K+ ATPase "sodium-potassium" pump.
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