Q: Which equation correctly represents the free energy change for ion transport across a membrane?

$$\Delta G = RT \ln \left( \frac{[\text{in}]}{[\text{out}]} \right) + zF\Delta\Psi$$

Question 1

Which of the following lipid compositions is most likely to correspond to the outer leaflet of a eukaryotic plasma membrane?

Accepted Answer

35% phosphatidylcholine, 15% gangliosides, 5% cholesterol, 45% other lipids

Question 2

A 20-residue segment from the mosquito protein Orco is likely to form a transmembrane alpha helix if it contains which of the following characteristics?

Accepted Answer

A stretch of mostly hydrophobic amino acids

Question 3

Which statement best describes the fluid mosaic model of biological membranes?

Accepted Answer

Membranes consist of a lipid bilayer with proteins and carbohydrates embedded and able to move laterally

Question 4

Which of the following is a consequence of hydrophobic mismatch between a transmembrane protein and the lipid bilayer?

Accepted Answer

The bilayer and/or protein may change conformation to minimize exposure of hydrophobic regions

Question 5

Which of the following best describes the function of SNARE proteins in vesicular transport?

Accepted Answer

They mediate the fusion of vesicle and target membranes by forming a tight complex

Question 6

Which equation correctly represents the free energy change for ion transport across a membrane?

Accepted Answer

$$\Delta G = RT \ln \left( \frac{[	ext{in}]}{[	ext{out}]} ight) + zF\Delta\Psi$$

Question 7

A mutation causes the hydrophobic region of a transmembrane protein to be shorter than the thickness of the lipid bilayer. What is the most likely result?

Accepted Answer

The bilayer will curve to cover the hydrophobic surface

Question 8

Which of the following is true about passive-mediated transport?

Accepted Answer

It involves transport proteins that facilitate movement down a concentration gradient

Question 9

The (Na$$^+$$–K$$^+)-$$ATPase pump moves ions in which direction and in what ratio?

Accepted Answer

3 Na$$^+$$ out, 2 K$$^+ in$$

Question 10

Which of the following statements about the selectivity of the K$$^+$$ channel is correct?

Accepted Answer

K$$^+$$ channels selectively allow K$$^+$$ ions to pass because their ionic radius fits the channel's carbonyl oxygen coordination

Question 11

A patient is given a drug that inhibits the (Na$$^+$$–K$$^+)-$$ATPase at step #5. What is the most likely physiological effect?

Accepted Answer

Cells will accumulate Na$$^+$$ and may swell and burst due to osmotic imbalance

Question 12

Which of the following best describes the role of cholesterol in the plasma membrane?

Accepted Answer

It increases membrane fluidity at low temperatures and decreases it at high temperatures

Question 13

Which of the following is a function of gangliosides in the plasma membrane?

Accepted Answer

Cell-cell recognition and signaling

Question 14

Which of the following best explains why phosphatidylserine is predominantly found in the inner leaflet of the plasma membrane?

Accepted Answer

It is negatively charged and involved in signaling pathways inside the cell

Question 15

Which process is responsible for the movement of proteins from the endoplasmic reticulum to the Golgi apparatus?

Accepted Answer

Vesicular transport mediated by COP and clathrin proteins

Question 16

Which of the following best describes the mechanism of glucose transport in the intestinal epithelium?

Accepted Answer

Secondary active transport using a Na$$^+-$$glucose symporter

Question 17

Which of the following is true about multi-pass alpha helix transmembrane proteins?

Accepted Answer

They contain multiple hydrophobic alpha helices that span the membrane

Question 18

Which of the following is a key feature of transport proteins that alternate between two conformations?

Accepted Answer

Ligand binding sites are accessible from only one side of the membrane at a time

Question 19

Which of the following is a correct statement about the role of small signaling sequences in protein trafficking?

Accepted Answer

They direct proteins to specific organelles such as the ER or Golgi

Lipids and Biological Membranes: Structure, Composition, and Transport

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