Ch 13 Text 1

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  1. ·         Permeability is conferred by three classes of membrane proteins: __, _, and __

    What does they each do? 
    pumps, carriers and channels

    • o   Pumps use a source of free energy to drive the thermodynamically uphill transport of ions or molecules; active transport
    • o   Carriers mediate the transport of ions and small molecules across the membrane without consumption of ATP
    • o   Channels provide a membrane pore through which ions can flow through; facilitated diffusion
  2. ·         Pumps are __ in that they do what? Two types of ATP-driven pumps, __ and __, undergo conformational changes on __ and __ that causes a bound ion to be transported across the membrane
    o   The __ is used to drive the movement of ions how?, a process referred to as __
    • energy transducers
    • convert one form of free energy into another
    • P-type ATPases and the ATP-binding cassette (ABC) transporters
    • ATP binding and hydrolysis
    • free energy of ATP hydrolysis
    • against their concentration gradients
    • primary active transport
  3. ·         Carriers utilize what to drive the transport of another against its gradient, termed __. (ex: E. coli lactose transporter)
    ·         Pumps can establish __.

    Specific ion channels can allow these ions to __; can allow some ions to flow freely while __ of others
    o   Opening of these channels is controlled by __
    • the gradient of one ion
    • secondary active transport

    • persistent gradients of particular ions across membranes
    • flow rapidly across membranes down these gradients
    • blocking the flow
    • the presence of certain ligands or a particular membrane voltage
  4. ·         The __, allows the flow of metabolites or ions between cells
    ·         Each cell type expresses a __. This collection of expressed transporters is important because it largely determines the __ and the __.
    o   In some senses, the cell-specific array of transporters defines the __ because a cell can execute only those biochemical reactions for which it has done what?
    • cell-to-cell channel, or gap junction
    • specific set of transporters in its plasma membrane
    • ionic composition inside cells
    • compounds that can be taken up from the cell’s environment
    • cell’s characteristics
    • taken up the necessary substrates
  5. ·         Two factors determine whether a molecule will cross a membrane: __ and __
    ·         __molecules  can pass through cell membranes because they __
    o   Molecules spontaneously move from a __ to __
    the permeability of the molecule in a lipid bilayer and the availability of an energy source

    • Lipophilic 
    • dissolve in the lipid bilayer, such as steroid hormones, which undergo simple diffusion
    • region of higher concentration to one of lower concentration
  6. ·         When a molecule is __, it is more complicated.

    For example, sodium is present at 143 mM outside a typical cell and at 14 mM inside the cell; yet, it does not __ because of __.
    o   The way they can do so is by __ through a channel, also called __ because the energy driving the ion movement originates from __, without any contribution by the __
    §  Channels display __ in that they facilitate the transport of some ions but not others
    • polar
    • freely enter the cell
    • its charge
    • facilitated diffusion
    • passive transport
    • the ion gradient itself
    • transport system
    • substrate specificity
  7. ·         How is the sodium gradient established in the first place?

    o   Sodium must move, or be pumped, against a concentration gradient. Because moving the ion from a low concentration to a higher concentration decreases entropy, it requires an input of free energy.
  8. §  Protein transporters embedded in the membrane are capable of using an __ to __. Because an input of energy from another source is required, this means of crossing the membrane is called __. 
    • energy source
    • move the molecule up a concentration gradient
    • active transport
  9. ·         An unequal distribution of molecules is an __ condition because __ is minimized when __; but, this requires __
    o   To quantify this free energy, we can look at the __ produced due to the unequal distribution; and, ions will be __
    • energy-rich
    • free energy
    • all concentrations are equal

    • free energy
    • electrical potential
    • repelled by like charges.
  10. §  The sum of the concentration and electrical terms is the __ or __. The free energy change is then determined by: dG=RT ln(c2/c1) +ZFdV,
    ·         Z is the __, dV is the __, and F is the __
    A transport process is active when__; when __, it is passive
    • electrochemical potential or membrane potential
    • electrical charge of the transported species
    • potential in volts across the membrane
    • Faraday constant

    •  dG is positive
    • dG is negative
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Ch 13 Text 1
2014-11-08 17:17:32
Test Three
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