Question 1

What is thought to be important in maintaining the native structure of the Kv channel membrane protein and promoting its function as a voltage-gated channel?

Accepted Answer

Negatively charged phospholipids, such as phosphatidylserine, are important for maintaining the proper orientation and stability of the Kv channel membrane protein. These phospholipids help to stabilize the voltage sensor domain and also play a role in the proper assembly of the channel protein within the membrane.

Question 2

A channel that opens in response to changes in ionic charge across a membrane is called a ________.

Accepted Answer

Voltage-gated channels open in response to changes in voltage or electrical potential across the membrane.

Question 3

What happens to phospholipid mobility when the cell is treated with agents that disrupt the underlying membrane skeleton?

Accepted Answer

Mobility is increased because agents that disrupt the underlying membrane skeleton remove the structural barriers or "fences" that normally restrict the diffusion of phospholipids, allowing them to move more freely within the membrane.

Question 4

Integral membrane proteins have been engineered to lack the portion that normally projects into the extracellular space. When the gene is inserted in cells, what happens to the mobility of this protein in the membrane?

Accepted Answer

Integral membrane proteins that lack the portion projecting into the extracellular space can move more freely within the membrane because they are not anchored or restricted by interactions with extracellular components, leading to a faster mobility rate compared to the wild type protein.

Question 5

Concentrated areas of sphingolipids and cholesterol that are more gelated and ordered than the surrounding fluid membrane are called ______________ .

Accepted Answer

The correct term for the concentrated areas of sphingolipids and cholesterol that are more gelated and ordered than the surrounding fluid membrane is lipid rafts. Lipid rafts are dynamic structures that play important roles in a variety of cellular processes, including cell signaling and membrane trafficking. Lipid rafts are also thought to be involved in disease processes such as Alzheimer's disease and HIV infection.

Question 6

Why would a transverse diffusion or flip-flop of membrane phospholipids from one leaflet to the other be so rare?

Accepted Answer

For flip-flop to occur, it would be necessary for the hydrophilic head of a phospholipid to move through the hydrophobic part of the bilayer, an extremely unlikely event.

Question 7

_________ is the movement of a substance from an area of high concentration to an area of lower concentration.

Accepted Answer

Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration. This process occurs naturally and does not require the input of energy.

Question 8

You fuse a mouse cell and a human cell and then treat the cell with anti-mouse or anti-human protein-directed antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins show green fluorescence; antibodies to human proteins show red fluorescence). What does the cell look like after one hour?

Accepted Answer

After one hour, the red and green labels are uniformly distributed across the entire membrane due to the fluid nature of the cell membrane, allowing proteins to move and mix.

Question 9

The movement of water through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration is called ________.

Accepted Answer

This process is specifically known as osmosis, as it involves the movement of water molecules across a semipermeable membrane based on differences in solute concentration. Diffusion refers to the movement of any molecule or particle from an area of high concentration to an area of low concentration, in the absence of a membrane or other barrier. Denaturation refers to the unfolding or disruption of a protein's structure, while metabolism refers to the chemical reactions and processes involved in maintaining life. Solubility refers to the ability of a substance to dissolve in a given solvent.

Question 10

Which substance will cross a plasma membrane most effectively?

Accepted Answer

The higher the octanol-water partition coefficient, the more hydrophobic or lipid soluble a molecule is, and the more it will cross a plasma membrane. Molecule AC has the highest octanol-water partition coefficient of 50, making it highly lipid soluble and able to cross the membrane most effectively.

Question 11

Why are proteins separated on an SDS polyacrylamide gel equally attracted to the positive electrode?

Accepted Answer

SDS is a negatively charged detergent that binds to and denatures proteins, causing them to unfold and become negatively charged. This results in proteins having a relatively uniform negative charge distribution, which causes them to be equally attracted to the positively charged electrode during electrophoresis.

Question 12

Which protein in the red blood cell membrane appears to be responsible for the exchange of bicarbonate ions and chloride ions across the red blood cell membrane?

Accepted Answer

Band 3 is a transmembrane protein in the red blood cell membrane that functions as an anion exchanger, facilitating the exchange of bicarbonate ions and chloride ions across the membrane.

Question 13

You modify the gene for an integral membrane protein so that the cytoplasmic portions of the protein are deleted. When the gene is inserted in cells, what happens to the mobility of this protein in the membrane?

Accepted Answer

Deleting the cytoplasmic portions of an integral membrane protein reduces the interaction of the protein with the cytoskeleton and other cytoplasmic components. This reduction in interactions allows the protein to move more freely within the membrane, leading to greater mobility compared to the intact protein.

Question 14

Which protein(s)below is(are)thought to be involved in and influence the stability of red blood cell membranes and the cells themselves by imparting strength, elasticity, and pliability to the membrane?

Accepted Answer

All of the proteins listed (actin and tropomyosin, spectrin, band 3, and ankyrin) play a role in maintaining the stability and integrity of red blood cell membranes by contributing to their strength, elasticity, and pliability.

Question 15

A channel that opens in response to the binding of a specific molecule, which is usually not the solute that passes through the channel is called a ________.

Accepted Answer

A ligand-gated channel responds to the binding of a specific molecule or ligand. The other options describe different types of gated channels but do not specifically mention the binding of a molecule to open the channel.

Question 16

You fuse a mouse cell and a human cell and then treat the cell with anti-mouse or anti-human protein-directed antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins show green fluorescence; antibodies to human proteins show red fluorescence). What does the cell look like immediately after fusion?

Accepted Answer

Immediately after fusion, the proteins from the mouse cell and the human cell have not yet had time to mix, so the cell would show distinct halves - one half labeled with green fluorescence (mouse proteins) and the other half with red fluorescence (human proteins).

Question 17

Usually, optical tweezers drag integral proteins a limited distance before they encounter a barrier that causes their release; upon release, they typically spring backward. What does this suggest?

Accepted Answer

The fact that the integral proteins encountered a barrier and then sprang backward suggests that the barrier is elastic, indicating that choice B is the best option. The other choices do not explain this observation.

Question 18

_________ is a technique that can be used to trap integral proteins and drag them through the membrane with a known force, using forces generated by a focused laser beam.

Accepted Answer

Optical tweezer manipulation can be used to trap integral proteins and drag them through the membrane with a known force, using forces generated by a focused laser beam. FRAP and fluorescence recovery after photobleaching are techniques used to study protein dynamics, SPT stands for single particle tracking and is used to study the movement of individual molecules, and SDS-PAGE is a technique used for protein separation and analysis.

Question 19

Which proteins move the farthest during SDS-polyacrylamide gel electrophoresis?

Accepted Answer

Smaller proteins move further during SDS-polyacrylamide gel electrophoresis because they experience less resistance from the gel matrix.

Question 20

Enzymes that move certain phospholipids between leaflets also have which of the following properties?

Accepted Answer

Enzymes that move certain phospholipids between leaflets are known as flippases, and their main function is to establish and maintain membrane lipid asymmetry by moving specific lipids from one leaflet to another. They do not have any role in interacting with neighboring cells or blocking signals. They also do not transport proteins across the membrane. Thus, option A is the correct choice.

Quiz 4: The Structure and Function of the Plasma Membrane