Q: Which equation is analogous to the Michaelis-Menten equation for the initial velocity of glucose accumulation inside a cell via GLUT1?

$$V_0$$ = \frac{V_{\text{max}} [S]_{\text{out}}}{K_t + [S]_{\text{out}}}$$

Question 1

Which structural feature distinguishes a micelle from a lipid bilayer, and what is the consequence for their formation in water?

Accepted Answer

Micelles form when the cross-sectional area of the head group is greater than that of the acyl side chain(s), resulting in spherical structures with hydrophobic interiors.

Question 2

Which equation describes the free-energy change for the transport of an uncharged solute from concentration $$C_1 to$$ $$C_2$$ across a membrane?

Accepted Answer

$$\Delta G_t = RT \ln\left(\frac{C_2$}{C_1$}\right)$$

Question 3

Which membrane protein type is most likely to be found reversibly associated with both the membrane and the cytosol, and what is a typical mechanism for this association?

Accepted Answer

Amphitropic proteins; association is often regulated by posttranslational modifications such as phosphorylation or lipid attachment.

Question 4

A membrane protein is predicted to have a single hydrophobic sequence of about 20 residues. Which type of membrane protein is this, and what is its likely topology?

Accepted Answer

Bitopic protein; it spans the bilayer once, with the hydrophobic sequence crossing the membrane.

Question 5

Which amino acid residues are most commonly found at the membrane interface, serving as anchors, and what is the rule for positively charged residues?

Accepted Answer

Tyrosine (Tyr) and Tryptophan (Trp) serve as anchors; Lysine (Lys) and Arginine (Arg) are more common on the cytoplasmic face (positive-inside rule).

Question 6

Which process is catalyzed by flippases, and what is the energy requirement?

Accepted Answer

Flippases catalyze the translocation of phosphatidylethanolamine (PE) and phosphatidylserine (PS) from the extracellular to the cytoplasmic leaflet, consuming ATP.

Question 7

Which membrane state is favored by long-chain saturated fatty acids at physiological temperatures, and what is the effect of unsaturated fatty acids?

Accepted Answer

Long-chain saturated fatty acids favor the liquid-ordered (Lo) state; unsaturated fatty acids introduce kinks that favor the liquid-disordered (Ld) state.

Question 8

Which equation describes the free-energy change for the transport of an ion across a membrane, considering both chemical and electrical gradients?

Accepted Answer

$$\Delta G_t = RT \ln\left(\frac{C_2$}{C_1$}\right) + ZF \Delta \psi$$

Question 9

Which transporter is responsible for basal glucose uptake in erythrocytes, and what is its kinetic constant ($$K_t$$)?

Accepted Answer

GLUT1; $$K_t = 3\ 	ext{mM}$$

Question 10

Which equation is analogous to the Michaelis-Menten equation for the initial velocity of glucose accumulation inside a cell via GLUT1?

Accepted Answer

$$V_0$$ = \frac{V_{	ext{max}} [S]_{	ext{out}}}{K_t + [S]_{	ext{out}}}$$

Question 11

Which type of membrane transport results in the accumulation of a solute above its equilibrium point, and what is the thermodynamic requirement?

Accepted Answer

Active transport; it is thermodynamically unfavorable (endergonic) and must be coupled to an exergonic process.

Question 12

Which family of ATP-driven transporters is responsible for multidrug resistance in tumor cells, and what is the gene encoding this transporter?

Accepted Answer

ABC transporters; the gene is ABCB1 (MDR1).

Question 13

Which membrane protein is defective in cystic fibrosis, and what is its normal function?

Accepted Answer

CFTR (ABCC7); it functions as a chloride ion channel.

Question 14

Which process is mediated by SNARE proteins, and what is their role in neurotransmitter release?

Accepted Answer

Membrane fusion; SNAREs mediate specific recognition and transient distortion of the bilayer to allow vesicle fusion during neurotransmitter release.

Question 15

Which membrane protein type is most likely to be found exclusively on the outer face of the plasma membrane, clustered in certain regions, and what is the anchoring mechanism?

Accepted Answer

GPI-anchored proteins; anchored by covalent attachment to glycosylphosphatidylinositol (GPI).

Question 16

Which membrane transport system is responsible for the electroneutral exchange of chloride and bicarbonate ions in erythrocytes, and what is its physiological significance?

Accepted Answer

Chloride-bicarbonate exchanger; it is essential for CO2 transport from tissues to the lungs.

Question 17

Which equation describes the general free-energy change for the conversion of a substrate to a product, and what do the terms represent?

Accepted Answer

$$\Delta G = \Delta G'^\circ + RT \ln\left(\frac{[P]}{[S]}\right)$$; $$\Delta G'^\circ is $$the standard free-energy change, $$R is $$the gas constant, $$T is $$temperature, $$[P]$$ and $$[S]$$ are product and substrate concentrations.

Question 18

Which membrane protein family is responsible for acidifying intracellular compartments, and what are the structural domains involved?

Accepted Answer

V-type ATPases; Vo domain is the proton channel, V1 domain contains the ATP-binding site and ATPase activity.

Biological Membranes and Transport: Structure, Dynamics, and Function

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