Question 1

An important aspect of transport by facilitated transporters and pumps is ________.
A)conformational shifts
B)rigidity
C)softness
D)$\alpha$-helix
E)$\beta$-pleated sheet

Accepted Answer

Facilitated transporters and pumps require conformational shifts to transport molecules across membranes. This involves changes in the shape of the transporter or pump protein to allow the molecule to be moved from one side of the membrane to the other. Rigidity or softness of the protein would not be as important in this process. The options involving F1F1F1S1 are not relevant as they do not relate to facilitated transport or pumps.

Question 2

You have fused a mouse cell and a human cell and then treated the cell with specific antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins - green; antibodies to human proteins - red).What does the cell look like immediately after fusion?
A)The cell is half red and half green.
B)The red and green labels are uniformly distributed across the entire membrane.
C)The red and green labels are distributed in intermingled patches.
D)The cell appears to be yellow in color.
E)The cell appears to be brown in color.

Accepted Answer

Immediately after fusion, the cell would appear half red and half green because the proteins from the mouse and human cells have not yet mixed in the membrane.

Question 3

A channel that opens in response to changes in ionic charge across a membrane is called a ________.
A)voltage-gated channel
B)charge-gated channel
C)ligand-gated channel
D)positive-gated channel
E)electric-gated channel

Accepted Answer

A channel that opens in response to changes in ionic charge across a membrane is called a voltage-gated channel. This is because the changes in charge are measured as a voltage difference, and the channel responds to this voltage difference by opening or closing.

Question 4

Why are the proteins being separated on an SDS polyacrylamide gel attracted equally to the positive electrode?
A)They carry a relatively uniform positive charge distribution
B)They carry a relatively uniform negative charge distribution.
C)They are all the same molecular weight.
D)They are all the same size.
E)They all have the same degree of hydrophobicity.

Accepted Answer

SDS (sodium dodecyl sulfate) is a negatively charged detergent that binds to proteins in a stoichiometric manner, such that each protein molecule binds a fixed amount of SDS per unit weight, giving it a uniformly negative charge. Therefore, in an SDS-PAGE gel, all the proteins would have a relatively uniform negative charge distribution and would be attracted equally to the positively charged electrode.

Question 5

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.
A)negatively charged cholesterol
B)positively charged sphingolipids
C)negatively charged phospholipids
D)positively charged phospholipids
E)negatively charged sphingolipids

Accepted Answer

Negatively charged phospholipids, such as phosphatidylserine and phosphatidylglycerol, are thought to be important in maintaining the native structure of the Kv channel and promoting its function as a voltage-gated channel. These phospholipids interact with positively charged residues in the protein structure, stabilizing the channel's conformation and enabling its voltage-sensitive gate to open and close in response to changes in membrane potential.

Question 6

_________ is the movement of a substance from an area of high concentration to an area of lower concentration.
A)Denaturation
B)Osmosis
C)Diffusion
D)Transport
E)Defusion

Accepted Answer

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, and it can occur across a membrane. This is a passive process that does not require energy. It is essential for the movement of nutrients, gases, and waste products in living organisms. Denaturation is the change in the shape of a protein or enzyme, Osmosis is the movement of water molecules across a semipermeable membrane, Transport refers to the movement of molecules across a biological membrane by specific proteins or pumps, and Defusion is not a known term in biology.

Question 7

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?
A)actin and tropomyosin
B)spectrin
C)band 3
D)ankyrin
E)All of these are correct.

Accepted Answer

Spectrin, ankyrin, and band 3 are all proteins that are involved in and influence the stability of red blood cell membranes and the cells themselves by imparting strength, elasticity, and pliability to the membrane.

Question 8

The movement of water through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration is called ________.
A)diffusion
B)osmosis
C)denaturation
D)metabolism
E)solubility

Accepted Answer

This process is specifically called osmosis, which is the diffusion of water molecules through a selectively permeable (semipermeable) membrane from regions of lower solute concentration to regions of higher solute concentration, in order to equalize the concentration of solutes.

Question 9

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?
A)glycophorin A
B)glycophorin D
C)band 3
D)glyceraldehyde 3-phosphate
E)alpha-actinin

Accepted Answer

Band 3 is a transmembrane protein that is responsible for the exchange of bicarbonate ions and chloride ions across the red blood cell membrane. Glycophorin A and D are glycoproteins that make up a large portion of the red blood cell membrane, but they do not play a role in ion exchange. Glyceraldehyde 3-phosphate is an enzyme involved in glycolysis and alpha-actinin is a cytoskeletal protein.

Question 10

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?
A)They move at a much greater rate than the wild type protein.
B)They move at a much smaller rate than the intact protein.
C)They do not move at all.
D)They are not inserted into the membrane so nothing can be learned about their mobility.
E)They flip to the opposite leaflet.

Accepted Answer

The extracellular domain often interacts with the extracellular matrix or other cells, which can restrict mobility. Without this domain, the protein may move more freely within the membrane.

Question 11

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 ________.
A)voltage-gated channel
B)charge-gated channel
C)ligand-gated channel
D)positive-gated channel
E)electric-gated channel

Accepted Answer

A channel that opens in response to the binding of a specific molecule is called a ligand-gated channel. This specific molecule is known as a ligand and it usually is not the solute that passes through the channel. Voltage-gated channels open in response to changes in electrical potential, whereas charge-gated channels do not exist. Positive-gated and electric-gated channels are not commonly used terms.

Question 12

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?
A)They move much greater distances than the intact protein.
B)They move much smaller distances than the intact protein.
C)They do not move at all.
D)They are not inserted into the membrane so nothing can be learned about their mobility.
E)They flip to the opposite leaflet.

Accepted Answer

The cytoplasmic portions of integral membrane proteins often interact with the cytoskeleton or other cellular components, restricting their mobility. Removing these portions can increase the protein's mobility within the membrane.

Question 13

What happens to phospholipid mobility when the cell is treated with agents that disrupt the underlying membrane skeleton?
A)Their mobility is unchanged.
B)Their mobility is increased because the fences that normally restrict their diffusion are removed.
C)Their mobility is decreased because the fences that normally restrict their diffusion are removed.
D)Their mobility is increased because the treatment raises the temperature.
E)Their mobility is decreased because the treatment lowers the temperature.

Accepted Answer

The disruption of the membrane skeleton removes the barriers that normally restrict phospholipid diffusion, thus increasing their mobility.

Question 14

Diffusion during which the substance to be transported binds selectively to a membrane-spanning protein,which helps the process along,is called ________.
A)osmosis
B)facilitated osmosis
C)simple diffusion
D)facilitated diffusion
E)active transport

Accepted Answer

Facilitated diffusion involves the use of membrane-spanning proteins to aid in the transport of specific substances across a membrane. This process does not require energy and is a type of passive transport. Osmosis is the diffusion of water across a selectively permeable membrane. Simple diffusion also does not involve the use of membrane-spanning proteins and relies solely on the concentration gradient of a substance. Active transport requires energy and moves substances against their concentration gradient. Facilitated osmosis is not a commonly used term in biology.

Question 15

What is the distinguishing characteristic of a P-type pump?
A)It must be pumped during the cycle.
B)It must be phosphorylated during the cycle.
C)It must be protonated during the cycle.
D)It must be deprotonated during the cycle.
E)It must be potassiumated during the cycle.

Accepted Answer

The distinguishing characteristic of a P-type pump is that it must be phosphorylated during the cycle. This is necessary for the conformational change that drives the transport of ions across the membrane.

Question 16

Which proteins move the farthest during SDS-polyacrylamide gel electrophoresis?
A)the largest
B)the smallest
C)the most negative
D)the most positive
E)both the largest and the most negative

Accepted Answer

During SDS-polyacrylamide gel electrophoresis, the proteins are denatured and coated with the negatively charged SDS molecule, which causes all proteins to have a uniform negative charge-to-mass ratio. Therefore, smaller proteins have a higher mobility in the gel matrix because they experience less steric hindrance and frictional resistance.

Question 17

The sodium-potassium pump makes the cell interior more ______ by pumping ____ sodium ions out of the cell for every ____ potassium ions pumped in.
A)negative,3,2
B)negative,2,3
C)positive,3,2
D)positive,2,3
E)negative,4,3

Accepted Answer

The sodium-potassium pump contributes to the cell's negative interior by actively transporting 3 sodium ions out of the cell and 2 potassium ions into the cell, using ATP for energy. This results in a higher concentration of positive ions outside the cell compared to inside, thus maintaining the negative charge of the cell interior.

Question 18

In the Na+/glucose cotransporter,_____ moving down its gradient drives the transport of _____ against its gradient.
A)Na+ ions,K+ ions
B)Na+ ions,glucose
C)glucose,Na+ ions
D)glucose,K+ ions
E)K+ ions,glucose

Accepted Answer

The Na+/glucose cotransporter uses the energy from Na+ ions moving down their concentration gradient to transport glucose against its concentration gradient into the cell.

Question 19

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?
A)the presence of solid barriers
B)the presence of elastic barriers
C)the attachment of the proteins to the cytoskeleton
D)the attachment of the proteins to the endoplasmic reticulum
E)the presence of rubber in the membrane

Accepted Answer

The fact that the proteins spring backward after encountering a barrier suggests the presence of elastic barriers, indicating that the membrane or cytoplasmic components have some elasticity, allowing the proteins to rebound. Solid barriers (A) or rubber in the membrane (E) would not allow for such rebounding behavior. Attachment of the proteins to the cytoskeleton (C) or endoplasmic reticulum (D) may affect their movement but does not explain the observed behavior.

Question 20

_________ 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.This yields information about the presence of membrane barriers.
A)FRAP
B)SPT
C)Fluorescence recovery after photobleaching
D)Optical tweezers
E)SDS-PAGE

Accepted Answer

Optical tweezers 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. This technique yields information about the presence of membrane barriers. FRAP and fluorescence recovery after photobleaching are techniques used to study protein mobility within the membrane, while SPT is used to study individual molecules in the membrane. SDS-PAGE is a technique used for protein separation and identification. Therefore, the best choice for the given question is D, Optical tweezers.

Quiz 4: The Structure and Function of the Plasma Membrane

An important aspect of transport by facilitated transporters and pumps is ________.

You have fused a mouse cell and a human cell and then treated the cell with specific antibodies that are covalently linked to fluorescent dyes (antibodies to mouse proteins - green; antibodies to human proteins - red) .What does the cell look like immediately after fusion?

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

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

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.

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

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?

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

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?

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?

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 ________.

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?

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

Diffusion during which the substance to be transported binds selectively to a membrane-spanning protein,which helps the process along,is called ________.

What is the distinguishing characteristic of a P-type pump?

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

The sodium-potassium pump makes the cell interior more __ by pumping sodium ions out of the cell for every potassium ions pumped in.

In the Na+/glucose cotransporter,_ moving down its gradient drives the transport of _ against its gradient.

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?

_________ 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.This yields information about the presence of membrane barriers.