Question 1

Yo u have the ability to measure the transport rate, Q, across a mem brane as a function of the concentration of tran spo rted s olute on the source side, S. How would you experimentally determine the Km for tra nsp ort?

A) It is the solute con centration at one-h alf the ma ximu m tran sport rate
B) It is the X -interc ept o n a p lot of 1 /Q aga inst 1 / S
C) It is the Y- interc ept o n a p lot of 1/Q aga inst 1/ S
D) It is the solute concentration when Q = Q max
E) It is -R tim es th e slop e of th e plot o f ln Q vs 1/T

A

Accepted Answer

KS (often denoted as Km in the context of Michaelis-Menten kinetics) is the solute concentration at which the transport rate is half of its maximum value (Qmax/2). This definition is used to characterize the affinity of the transporter for the solute.

Question 2

A facilitated diffusion carrier has a Km = 5 m M an d a m axim um transport rate of Q max. At a s olute concentration of 10 mM, its transport rate is about&#10;A) 0.25 Qmax&#10;B) 0.5 Qmax&#10;C) 0.67 Qmax&#10;D) 2 Q max&#10;E) Q max

Accepted Answer

The transport rate at a given solute concentration can be estimated using the Michaelis-Menten equation, which in this context is $V = \frac{V_{max} \times [S]}{K_M + [S]}$, where $V$ is the rate of transport, $V_{max}$ is the maximum transport rate, $[S]$ is the solute concentration, and $K_M$ is the Michaelis constant (in this case, 5 mM). Plugging in the given values ($V_{max} = Q_{max}$ and $[S] = 10 mM$), we get $V = \frac{Q_{max} \times 10 mM}{5 mM + 10 mM} = \frac{2}{3} Q_{max}$, which is approximately 0.67 $Q_{max}$.

Question 3

A mem brane separates a solution with a concentration CL on the left and CR on the right. The free energy change for movem ent of solute to the right is zero when&#10;A) C L < CR&#10;B) C L = RT Ln C L / CR&#10;C) C R = RT Ln C L / CR&#10;D) C L = CR&#10;E) p = 0

Accepted Answer

The free energy change for the movement of solute across a membrane is zero when the concentration on both sides of the membrane is equal, which is what choice D states (CL = CR). This condition represents equilibrium, where there is no net movement of solute across the membrane.

Question 4

In th e lip id- dis so lutio n m od el o f pa ss ive tra ns po rt, th e ra te- lim iting ste p in the pe rm ea tion is&#10;A) Dissolution of the solute in the lipid phase on the source side of the mem brane&#10;B) Dissolution of the solute in the aqueous phase on the sink side of the mem brane&#10;C) Diffusion of the solute through the lipid interior of the membrane&#10;D) Conformational changes in the carrier&#10;E) The num ber of pores in the mem brane.

Accepted Answer

The lipid-dissolution model of passive transport emphasizes that the rate-limiting step in the permeation of a solute is its diffusion through the lipid interior of the membrane. This is because the lipid bilayer acts as a barrier to the solute, and the rate at which the solute can cross this barrier by diffusing through the lipid phase is what ultimately determines the rate of transport across the membrane.

Question 5

An ionophore is a substance that&#10;A) Increases the permeability of a mem brane to glucose&#10;B) Se para tes p rotein s on the b asis of the ir cha rge a nd s ize&#10;C) Carries water across mem branes&#10;D) Increases the permeability of a membrane to ions&#10;E) Enlarges the size of water pores

Accepted Answer

Ionophores are compounds that facilitate the transport of ions across the lipid membranes of cells, thereby increasing the membrane's permeability to specific ions.

Question 6

Facilitated diffusion differs from simple passive permeability in all of the following EXCEPT&#10;A) Facilitated diffusion is saturable, passive permeability is not&#10;B) Facilitated diffusion uses metabolic energy, passive permeability does not&#10;C) Facilitated diffusion is specific, passive permeability is not&#10;D) Facilitated diffusion displays competitive inhibition, passive permeability does not&#10;E) Facilitated diffusion uses a carrier, passive permeability does not

Accepted Answer

Facilitated diffusion, like simple passive permeability, does not use metabolic energy. Both processes rely on the concentration gradient, without the need for ATP.

Question 7

W hen a solute penetrates through a mem brane by dis so lvin g in the lipid , the pe rm ea bility is dire ctly proportional to the&#10;A) Size o f the s olute&#10;B) Partition coefficient&#10;C) Tem perature&#10;D) Thickness of the mem brane&#10;E) Concentration difference across the mem brane

Accepted Answer

The permeability of a solute that dissolves in the lipid layer of a membrane is directly proportional to the partition coefficient. This coefficient measures how well the solute dissolves in the lipid compared to an aqueous phase, affecting its ability to penetrate the membrane.

Question 8

Permeability through the lipid bilayer&#10;A) Requires an input of metabolic energy&#10;B) Sa turate s with highe r con cen tration o f solu te&#10;C) Always involves mo vem ent of solute from low to high osm otic pressure&#10;D) Depends directly on the partition coefficient&#10;E) Is incr eas ed b y ionization o f the s olute

Accepted Answer

Permeability through the lipid bilayer depends directly on the partition coefficient because substances that are more lipophilic (having a higher partition coefficient) can more easily diffuse through the lipid bilayer without the need for energy input, transport proteins, or moving against a concentration gradient.

Question 9

In carrier kinetics, saturation means that&#10;A) All of the ca rriers are b usy a nd trans po rt is limited by the num ber o f carriers&#10;B) N o m or e tr an sp or t is p os sib le&#10;C) Equilibrium has been reached&#10;D) The m em bran e ca n ho ld no m ore s olute&#10;E) There are no free C=C double bonds

Accepted Answer

Saturation in carrier kinetics occurs when all carriers are occupied, meaning transport across the membrane is at its maximum and limited by the number of carriers available. This does not imply no more transport is possible or that the membrane is physically full; it simply means the rate of transport cannot increase further with an increase in solute concentration because all carrier proteins are already in use.

Question 10

In the microporous model of a mem brane, solutes diffuse across the mem brane by&#10;A) Dissolving in the lipid and diffusing across the lipid phase&#10;B) Diffusing through water-filled channels, or pores&#10;C) Being bound to carriers that diffuse across the mem brane&#10;D) Obtaining enough energy through splitting of ATP&#10;E) Riding down the electrochemical gradient of Na+

Accepted Answer

In the microporous model of a membrane, solutes diffuse across the membrane through water-filled channels or pores. This model describes the movement of water-soluble substances that cannot easily diffuse through the lipid bilayer.

Question 11

Vo ltage- gate d ch ann els c han ge th eir op en p roba bility in res pon se to&#10;A) Chem icals that bind to the channel&#10;B) Current that flows through the channel&#10;C) The loc al ele ctrica l field&#10;D) Binding of ions to the channel&#10;E) Phosphorylation of the channel

Accepted Answer

The answer of Vo ltage- gate d ch ann els...

Question 12

Which of the following is NOT a characteristic of biological ion channels?&#10;A) They disp lay spe cificity&#10;B) They often display gating&#10;C) The y are passive&#10;D) They are integral proteins&#10;E) They are c arriers

Accepted Answer

The answer of Which of the following is NOT a...

Question 13

Permeability is best defined for any mem brane as&#10;A) n wa2 D / &#240;&#10;B) J / 6 C &#240;&#10;C) k s D lipid /&#10;D) D / &#240;&#10;E) (n w a2 D + k

Accepted Answer

The answer of Permeability is best defined for any mem...

Question 14

Gating of ion channels means that the&#10;A) Sp ecificity of ion con duc tanc e is de term ined by a ga te&#10;B) Ch an ne ls appear to have gates that are opened sometimes, and closed at other times&#10;C) Channels behave like sieves&#10;D) Channels are like circular pipes with pressure-operated valves&#10;E) Opening of the channels is metabolically controlled

Accepted Answer

The answer of Gating of ion channels means that the&#10;A)...

Question 15

Ex plain w hy at ste ady-s tate the con cen tration g radie nt in a p ore m ust b e co nsta nt.

Accepted Answer

The answer of Ex plain w hy at ste ady-s...

Question 16

In the microporous mem brane model, transport flux is Increased by&#10;A) Increasing the thickness of the mem brane&#10;B) Increasing the length of each pore&#10;C) Decreasing the difference in concentration across the mem brane&#10;D) Incre asin g the size of the s olute&#10;E) Increasing the number of pores per unit area of membrane

Accepted Answer

The answer of In the microporous mem brane model, transport...

Deck 10: Passive Transport and Facilitated Diffusion