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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
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
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
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
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
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 __.
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
Two factors determine whether a molecule will cross a membrane: __ and __
__molecules can pass through cell membranes because they __
Molecules spontaneously move from a __ to __
the permeability of the molecule in a lipid bilayer and the availability of an energy source
- dissolve in the lipid bilayer, such as steroid hormones, which undergo simple diffusion
- region of higher concentration to one of lower concentration
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 __.
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
- freely enter the cell
- its charge
- facilitated diffusion
- passive transport
- the ion gradient itself
- transport system
- substrate specificity
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.
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
An unequal distribution of molecules is an __ condition because __ is minimized when __; but, this requires __
To quantify this free energy, we can look at the __ produced due to the unequal distribution; and, ions will be __
- free energy
- all concentrations are equal
- free energy
- electrical potential
- repelled by like charges.
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