Chapter 12 A molecule moves down its concentration gradient by transport but requires transport to move up its concentration gradient Transporter proteins and ion channels function in membrane transport by providing a pathway through the membrane for specific polar solutes or inorganic ions are highly selective in the solutes they transport binding the solute at a specific site and changing conformation so as to transport the solute across the membrane On the other hand discriminate between solutes mainly on the basis of size and electrical charge hydrophilic hydrophobic ion channels noncovalent passive transporter proteins active amino acid amphipathic Fill in table For an uncharged molecule the direction of passive transport across a membrane is determined solely by its gradient On the other hand for a charged molecule the must also be considered The net driving force for a charged molecule across a membrane therefore has two components and is referred to as the gradient Active transport allows the movement of solutes against this gradient The transporter proteins called transporters use the movement of one solute down its gradient to provide the energy to drive the uphill transport of a second solute When this transporter moves both ions in the same direction across the membrane it is considered a n if the ions move in opposite directions the transporter is considered a n antiport ATP hydrolysis concentration coupled electrochemical light driven membrane potential symport uniport The action potential is a wave of that spreads rapidly along the neuronal plasma membrane This wave is triggered by a local change in the membrane potential to a value that is negative than the resting membrane potential The action potential is propagated by the opening of gated channels During an action potential the membrane potential changes from to The action potential travels along the neuron s to the nerve terminals Neurons chiefly receive signals at their highly branched anions axon cytoskeleton dendrites depolarization hyperpolarization less ligand more negative neutral positive pressure synaptic vesicle voltage Figure illustrates changes in membrane potential during the formation of an action potential What membrane characteristic or measurement used to study action potentials is indicated by each arrow Which of the following statements are correct Explain your answer 1 The plasma membrane is highly impermeable to all charged molecules True False 2 CO2 and O2 are water soluble molecules that diffuse freely across cell membranes True False 3 K ions is the most abundant outside a typical mammalian cell True False 4 For a cell to avoid being torn apart by electrical forces the quantity of positive charge inside the cell must be balanced by an almost exactly equal quantity of negative charge and the same is true for the charge in the surrounding fluid True False 5 The differences in permeability between artificial lipid bilayers and cell membranes arise from variations in phospholipid content True False 6 Channels have specific binding pockets for the solute molecules they allow to pass True False 7 Transporters allow solutes to cross a membrane at much faster rates than do channels True False 8 Facilitated diffusion passive transport can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient True False 9 Transporters undergo transitions between different conformations depending on whether the substrate binding pocket is empty or occupied True False 10 The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter True False 11 The ion selectivity of a channel depends solely on the charge of the amino acids lining the pore inside the channel True False 12 The plasma membrane of many animal cells contains open K channels yet the K concentration in the cytosol is much higher than outside the cell True False 13 Most ion channels are gated which allows them to open and close in response to a specific stimulus rather than allowing the constant unregulated flow of ions True False 14 The membrane potential of an axon temporarily becomes more negative when an action potential excites it True False 15 Action potentials are usually mediated by voltage gated Ca2 channels True False 16 Voltage gated Na channels become automatically inactivated shortly after opening which ensures that the action potential cannot move backward along the axon True False 17 Voltage gated K channels also open immediately in response to local depolarization reducing the magnitude of the action potential True False 18 The resting potential is restored by an efflux of K through voltage gated K channels and K leak channels True False
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