Question 1

Which of the following will not solubilize a typical peripheral membrane protein?

Accepted Answer

Peripheral membrane proteins are associated with the membrane through electrostatic interactions and hydrogen bonds, rather than hydrophobic interactions. Detergents, extreme pH, and high salt concentrations can disrupt these interactions, solubilizing the proteins. However, mildly hypertonic saline would not disrupt these interactions significantly enough to solubilize the protein, as it primarily affects the osmotic balance without directly disrupting protein-membrane interactions.

Question 2

A feature common to most transmembrane proteins is a(n)

Accepted Answer

The F1F1F1S1F1F1F10-helical region of about 20 to 25 hydrophobic amino acids is a common feature of transmembrane proteins, as it allows them to embed into the hydrophobic interior of the lipid bilayer. Options A, C, and D do not accurately describe typical features of transmembrane proteins.

Question 3

Which of the following are integral membrane proteins that do not contain a transmembrane $\alpha$ helix?

Accepted Answer

Glycosylphosphatidylinositol (GPI)-anchored proteins do not contain a transmembrane helix. Band 3 and glycophorins both contain a single transmembrane helix, while spectrins are peripheral membrane proteins that interact with the membrane indirectly.

Question 4

Membrane proteins are able to move

Accepted Answer

Membrane proteins are able to move laterally within the plane of a membrane, but not from the inner to the outer surface or from apical to basal surfaces. They do not necessarily need to be attached to microtubules or microfilaments to move.

Question 5

Which of the following lipids are distinctly enriched in lipid rafts?

Accepted Answer

Cholesterol and sphingolipids are distinctly enriched in lipid rafts as they have longer and saturated fatty acid chains, which allow them to form tighter packing and more stable microdomains. Glycolipids, phosphatidylinositol, phosphatidylcholine, and phosphatidylethanolamine are found in both lipid rafts and non-raft regions.

Question 6

Which statement about the glucose transporter is false?

Accepted Answer

Flow through the glucose transporter is bidirectional, as it allows glucose to enter or exit the cell depending on the concentration gradient.

Question 7

Which statement about ion channels is true?

Accepted Answer

Ion channels are opened by the binding of ligands or by changes in electric potential across the membrane. This allows ions to pass through the channel, down their concentration gradient, without the need for energy input (such as ATP). Ion channels can be either open or closed, but they are typically closed most of the time and only open in response to a stimulus. The rate of transport through ion channels is very fast, often exceeding the rate of transport through carrier proteins.

Question 8

The resting plasma membrane potential as described by the Nernst equation is the sum of the movement of many ions. However, in practice, the movement of _______, a single ion, is the major component determining membrane potential.

Accepted Answer

The major component determining membrane potential is potassium (K+), as its movement across the membrane significantly influences the resting membrane potential according to the Nernst equation.

Question 9

Which statement about the relative concentrations of Na⁺ and K⁺ inside and outside of a typical mammalian cell is true?

Accepted Answer

This is because the concentration of Na+ and Cl- ions is higher outside the cell, while the concentration of K+ ions is higher inside the cell. The difference in concentration is maintained by the sodium-potassium pump. The statement in option A is not entirely true because the concentration of K+ ions outside the cell is very low, about 1/30th of the concentration inside the cell. Option C is not correct because the question is about sodium and potassium ions, not chloride ions. Option D is incorrect because the concentration of Na+ ions outside the cell is higher than inside the cell.

Question 10

Although Na⁺ is smaller than K⁺, its passage through the K⁺ channel is blocked by the _______ filter.

Accepted Answer

The sentence is discussing the passage of Na⁺ through the K⁺ channel. Therefore, the missing word must describe something about the channel that blocks the passage. The phrases "negativity" and "positivity" do not make sense in this context. However, "selectivity" makes sense as an explanation for a channel blocking certain molecules or ions. Therefore, the best choice is D. As for the other choices, CO₂ is not a known filter or term in this context, so A is incorrect.

Question 11

Transport of glucose into the intestinal epithelium is driven by ion gradients established by the

Accepted Answer

Glucose transport into the intestinal epithelium is powered by the sodium gradient, which is established by the Na⁺-K⁺ pump. This pump uses ATP to move sodium ions out of the epithelial cells and into the extracellular fluid, creating a concentration gradient that drives the entry of glucose through a co-transporter known as ⁺. Therefore, the correct answer is C.

Question 12

Active transport differs from facilitated diffusion in that

Accepted Answer

Active transport requires energy to move molecules against their concentration gradient, whereas facilitated diffusion does not require energy and moves molecules down their concentration gradient.

Question 13

Which statement about ABC transporters is false?

Accepted Answer

ABC transporters are not all Cl^- channels, although some members of the family do have this structure. The other statements are true: each family member has an ATP-binding cassette, they are the largest family of membrane transporters in humans, and each member of the family has shared domain structure features.

Question 14

The ingestion of large particles by cells is a form of endocytosis known as

Accepted Answer

The ingestion of large particles by cells is known as phagocytosis. Fluid phase endocytosis involves the ingestion of soluble molecules, macropinocytosis involves the ingestion of large volumes of extracellular fluid, and transcytosis involves the transport of macromolecules across a cell.

Question 15

Which of the following is not involved in receptor-mediated endocytosis?

Accepted Answer

Pseudopodia are involved in phagocytosis, not receptor-mediated endocytosis. Receptor-mediated endocytosis involves the formation of clathrin-coated pits and the recruitment of adaptor proteins and internalization signals.

Question 16

LDL uptake by cells is one of the functions of

Accepted Answer

LDL uptake by cells is specifically mediated by receptors on the surface of cells that recognize and bind to LDL particles, leading to their internalization via receptor-mediated endocytosis. Phagocytosis is the process by which cells engulf and internalize large particles such as bacteria, while caveolae are small invaginations on the cell surface that play a role in signaling and trafficking. ABC transporters are a family of proteins that play a role in transporting a variety of molecules across cellular membranes.

Question 17

Mutations in the internalization signal of endocytic receptors prevent their interaction with

Accepted Answer

Mutations in the internalization signal of endocytic receptors prevent their interaction with adaptor proteins, which are crucial for linking receptors to clathrin-coated pits during endocytosis.

Question 18

The pH of endosomes and lysosomes is

Accepted Answer

Endosomes and lysosomes have a low pH (acidic) environment, typically around 4.5-5.5. This acidic environment is important for the breakdown of ingested material and the function of lysosomal enzymes.

Question 19

In their acceptance speech for the Nobel Prize in 1985, Michael Brown and Joseph Goldstein said, "Cholesterol is a Janus-faced molecule. The very property that makes it useful in cell membranes, namely its absolute insolubility in water, also makes it lethal." Explain this remark.

Accepted Answer

The answer of In their acceptance speech for the Nobel...

Question 20

Detergents are used to solubilize membranes because they are dual molecules possessing both hydrophobic and hydrophilic portions. Why are they also used as cleaning reagents (to clean, for example, clothes and dishes)?

Accepted Answer

The answer of Detergents are used to solubilize membranes because...

Quiz 15: The Plasma Membrane