Download Cytogenetics Lesson 7: The Cell Cycle, Na+ Pump & K+ Channels and more Study notes Biology in PDF only on Docsity! CYTOGENETICS Lesson 7 [TRANS] LESSON 07: THE CELL CYCLE NA+ PUMP & K+ CHANNELS โ It is how membrane potential is maintained โ The Na pump uses the energy of ATP hydrolysis to pump Na+ out of animal cells and K+ in. In this way, the pump helps keep the cytosolic concentrations of NA+ low and K+ high โ โ โNa is extracellular cation, and K is intracellular cationโ NEURONAL COMMUNICATION NA+ PUMP โ Accounts for 30% of ATP-use โ Pumps Na+ out, carries K+ in โ Also known as Na+-K+ ATPase or the Na+-K+ pump โ 3 Na+ out โ 2 K+ in โ Creates a steep concentration gradient of both ions โ Na+ gradient produces most energy โ โIn this case Na is higher concentration outside. Each time it pumps out 3 Na+ ions and carries in 2 K+ ions, so dili equal ang transport sa ion. That is why the outside is more positive than the inside of the cellโ TAKEAWAYS โ The lipid bilayer of cell membranes is highly permeable to small, non- polar molecules such as oxygen and carbon dioxide and, to a lesser extent, to very small, polar molecules such as water. It is highly impermeable to most large, water-soluble molecules and to all ions. โ Transfer of nutrients, metabolites, and inorganic ions across cell membranes depends on membrane transport proteins. โ Cell membranes contain a variety of transport proteins that function either as transporters or channels, each responsible for the transfer of a particular type of solute. โ Channel proteins form pores across the lipid bilayer through which solutes can passively diffuse. โ Both transporters and channels can mediate passive transport, in which an uncharged solute moves spontaneously down its concen- tration gradient. โ For the passive transport of a charged solute, its electrochemical gradient determines its direction of movement, rather than its con- centration gradient alone. โ Transporters can act as pumps to mediate active transport, in which solutes are moved uphill against their concentration or electrochemi- cal gradients; this process requires energy that is provided by ATP hydrolysis, a downhill flow of Na+ or H+ ions, or sunlight. โ Transporters transfer specific solutes across a membrane by under- going conformational changes that expose the solute-binding site first on one side of the membrane and then on the other. โ The Na+ pump in the plasma membrane of animal cells is an ATPase; it actively transports Na+ out of the cell and K+ in, maintaining a steep Na+ gradient across the plasma membrane that is used to drive other active transport processes and to convey electrical signals. โ Ion channels allow inorganic ions of appropriate size and charge to cross the membrane. Most are gated and open transiently in response to a specific stimulus. โ Even when activated by a specific stimulus, ion channels do not remain continuously open: they flicker randomly between open and closed conformations. An activating stimulus increases the propor- tion of time that the channel spends in the open state. โ The membrane potential is determined by the unequal distribution of charged ions on the two sides of a cell membrane; it is altered when these ions flow through open ion channels in the membrane. โ In most animal cells, the negative value of the resting membrane potential across the plasma membrane depends mainly on the K+ gradient and the operation of K+-selective leak channels; at this rest- ing potential, the driving force for the movement of K+ across the membrane is almost zero. โ Neurons produce electrical impulses in the form of action potentials, which can travel long distances along an axon without weaken- ing. Action potentials are propagated by voltage-gated Na+ and K+ channels that open sequentially in response to depolarization of the plasma membrane. โ Voltage-gated Ca2+ channels in a nerve terminal couple the arrival of an action potential 1
