Plant Physiology Ch. 6 Solute Transport | Quizlet

Molecular and ionic movement from one location to another is known as..

transport

The spontaneous "downhill" movement of molecules is termed...

passive transport

What happens in passive transport at equilibrium?

no further net movements of solutes can occur without the application of a driving force

The movement of substances against a gradient of chemical potential, or "uphill," is termed...

active transport

Is active transport spontaneous or not spontaneous?

not spontaneous. it requires that work be done on the system by the application of cellular energy

- can accomplish this task by coupling transport to the hydrolysis of ATP

Biological transport can be driven by four major forces:

concentration, hydrostatic pressure, gravity, and electric fields

The _________________ for any solute is defined as the sum of the concentration, electrical, and hydrostatic potentials

chemical potential

What is the importance of the concept of chemical potential?

It sums all the forces that may act on a molecule to drive net transport

Neutral solutes have ________________ influenced by _______________

chemical potential; mass-action potential

Charged solutes have both a chemical potential and a charge component =

electrochemical potential

__________________ is a voltage across a membrane that influences the distribution of charges solutes across a membrane

membrane potential

µj (chemical potential) =

µj (chemical potential of j under standard conditions) + RTlnCj (concentration component) + zjFE (electrical potential component) + VjP (hydrostatic pressure component)

µjA > µjB means..

passive transport occurs spontaneously down a chemical-potential gradient

µjA = µjB means..

at equilibrium. If there is no active transport, steady state occurs

µjA < µjB means..

active transport occurs against a chemical-potential gradient

ΔG per mole for movement of j from A to B is equal to..

µjB - µjA

For an overall negative ΔG, the reaction must be coupled to a process that has a ΔG more negative than...

-(µjB - µjA)

Diffusion (passive transport) always moves molecules energetically downhill from areas of...

higher chemical potential to areas of lower chemical potential

Movement against a chemical-potential gradient is indicative of..

active transport

µsi =

µs* + RTlnCsi

What is the equation fo the chemical potential of sucrose inside a cell?

µs^i = µs* + RTlnCs^i

What is the equation for the chemical potential of sucrose outside the cell?

µs^o = µs* + RTlnCs^o

What is the equation for the difference in the chemical potential of sucrose between the solutions inside and outside the cell?

RTln([S]c/[S]o)

If the sucrose different in chemical potential is negative, then...

sucrose can diffuse inward spontaneously

A postive +Δµs =

energy must be applied to move solute into the cytosol

A negative -Δµs =

passive transport into the cell

Ions have ___________ and ____________ potential

electrical and chemical

- electrochemical potential

What is the equation for electrochemical potential and what do the components mean?

µI = µ^oI + RT*ln[I] + zFE

µ^oI = standard electrochemical potential of I (ion) at 1 M

z = valence of the ion (K+ = +1, Mg2 = +2, Cl- = -1, etc.)

F = Faraday constant (96,500 coulombsmol-1) (coulomb = JV-1)

E = electrical potential of the medium in volts (V)

What is the equation for the electrochemical potential difference?

ΔµI = (µI)c - (µI)o = RTln([I]c/ [I]o) + zFDE

ΔE = Eo - Ec =

electrochemical potential difference (volts) between two aqueous media separated by a membrane

A membrane with a charge across it is..

polarized

How can an ion move passively against its concentration gradient?

if the appropriate voltage (electric field) is applied between two compartments

The extent to which a membrane permits the movement of a substance is called the..

membrane permeability

When salts diffuse across a membrane, an _______________ can develop

electrical membrane potential (voltage)

A potential that develops as a result of diffusion is called a..

diffusion potential

Membrane potentials collapse (=0mv) as charge gradients reach..

0

If the concentration of potassium chloride is higher in compartment A ([KClA > [KCL]B), ptassium and chloride ions will diffuse into..

compartment B

If the membrane is more permeable to potassium ions than to chloride ions, potassium ions will diffuse _________ than chloride ions, and a charge separation will develop, resulting in establishment of a ________________

faster; diffusion potential

When concentrations don't collapse, what happens?

membrane potential is maintained

Membranes affect _________, but not. ___________

rate; final equilibrium

What does the Nernst equation state?

that at equilibrium, the difference in concentration of an ion between two compartments is balanced by the voltage difference between the compartments

An ion at equilibrium will have the same _________________ inside and out

electrochemical potential

What is the Nernst equation?

ΔE = (2.3RT/zF)(log[Io/Ic])

The Nernst equation can be further simplified for a univalent cation at 25C..

ΔE = 59 mV (log[Io/Ic]).

A membrane potential of -59 mV will "hold" a ____________ concentration gradient across the membrane for a monovalent cation

tenfold

The Nernst equation can be used at any time to determine..

whether a given ion is at equilibrium across a membrane

- distinction must be made between equilibrium and steady state

______________ is the condition in which influx and efflux of a given solute are equal, and therefore the ion concentrations are constant over time

steady state

A modified version of the Nernst equation, the ________________, includes all permeant ions and therefore gives a more accurate value for the diffusion potential

Goldman equation

_________________ is a major determinant of the membrane potential

Proton transport

Any active transport mechanism that results in the movement of a net electric charge will tend to move the membrane potential away from the value predicted by the Goldman equation. Such transport mechanisms are called..

electrogenic pumps

- common in living cells

The membrane potential of plant cells have two components:

a diffusion potential and a component resulting from electrogenic ion transport

The term transport proteins encompasses three main categories:

channels, carriers, and pumps

What is the proton motive force (PMF)?

the free energy stored in an electrochemical for H+, expressed in mV

What is permeable to small non-polar molecules?

pure lipid bilayer

biological membranes are also permeable to...

ionic, polar, and larger molecules

Proteins facilitate _________ and _________ movement of solute across membranes

active and passive

_____________ are transmembrane proteins that function as selective pores through which ions, and in some cases neutral molecules, can diffuse through the membrane

Channels

Transport through channels is always ____________, and the specificity of transport depends on ______________ and _________ more than on _______________

passive; pore size; electric charge; selective binding

As long as the channel pore is open, substances that can penetrate the pore diffuse through it extremely..

rapidly

- channel pores are not open all of the time

Channel proteins contain particular regions called ________ that open and close the pore in response to signals

gates

Signals that can regulate channel activity include..

membrane potential changes, ligands, hormones, light, and posttranslational modification as phosphorylation

____________ specialize in the transport of specific inorganic ions as well as other organic metabolites

Carriers

Carrier proteins are..

facilitators mostly for organics and some ions, very selective, substrate binds to protein, conformational change in protein, slower (100s-1000s molecules/second)

Channel proteins are...

'pores' through the membrane that transport mostly ions, selective (e.g. K+ >> Na+), no direct interaction between solute and protein, very fast (~108 ions/second!), regulated by "gating" (either opened or closed)

_____________ open or close in response to membrane potential:

Inward rectifying K+ channels open when the membrane is hyperpolarized and let K+ in; outward rectifying K+ channels open when the membrane potential is low and let K+ out

Voltage gated channels

Passive transport via a carrier is sometimes called ____________, although it resembles diffusion only in that it transports substances down their gradient of electrochemical potential, without an additional input of energy

facilitated diffusion

To carry out active transport, what must happen?

a carrier must couple the energetically uphill transport of a solute with another, energy-releasing event so that the overall free-energy change is negative

__________________ is coupled directly to a source of energy other than Δµj, such as ATP hydrolysis, an oxidation-reduction reaction, or the absorption of light by the carrier protein

Primary active transport

Membrane proteins that carry out primary active transport are called..

pumps

Most pumps transport..

inorganic ions

____________________ refers to ion transport involving the net movement of charge across the membrane

electrogenic transport

____________________ involves no net movement of charge

electroneutral transport

The ____________ generates the gradient of electrochemical potential of H+ across the plasma membrane

plasma membrane H+ -ATPase

the ____________ and the _____________ electrogenically pump protons into the lumen of the vacuole and the Golgi cisternae

vacuolar H+ -ATPase; H+-pyrophosphatase

________________ uses the proton gradient created by primary active transport (the proton motive force)

secondary active transport

Secondary active transport is driven indirectly by..

pumps

There are two types of secondary active transport:

symport and antiport

What is symport?

the two substances move in the same direction through the membrane

What is antiport?

coupled transport in which the energetically downhill movement of one solute drives the active transport of another solute in the opposite direction

Which of the following best describes the chemical potential of a neutral solute across a membrane?

ΔGx = 2.303RT*log([X]c/[X]o]

Which of the following can contribute to the membrane potential of a plant cell?

- Negatively charged macromolecules (proteins, nucleic acids) being held inside the cell

- P-type ATPases pumping protons out of the cell at the expense of ATP

- Cations moving out of a cell down a concentration gradient

ΔG = RT*ln([I]c/[I]o) + zFΔE is the electrochemical potential difference of an ion. Based on this equation, name at least three variables that contribute to the distribution of the ion?

- valence of the ion(K+=1, Cl-=-1, Mg2+=2)

- electrical potential of medium(volts)

-concentration inside/outside of cell