Chapter 12: Membrane Structure and Function

Question 1

Which of the following is TRUE?

Answer 1

1. Membranes are lipid bilayers.
2. Membrane lipids have both hydrophobic and hydrophilic properties.
3. Many membranes are electrically polarized.

Question 2

Which of the following membranes would be most fluid?

a. A bilayer made of lipids with saturated 16-carbon fatty acids.
b. A bilayer made of lipids with saturated 18-carbon fatty acids.
c. A bilayer made of lipids with polyunsaturated 16-carbon fatty acids.
d. A bilayer made of lipids with polyunsaturated 18-carbon fatty acids.

Answer 2

C. A bilayer made of lipids with polyunsaturated 16-carbon fatty acids.

Question 3

Which of the following statements is consistent with the structure of biological membranes?

Answer 3

The membrane lipids self-assemble to form the lipid bilayer

Question 4

An antiporter and a symporter are examples of:

Answer 4

A secondary transporter

Question 5

Carbohydrate residues attatched to the membrane lipids are:

Answer 5

Always positioned on the extracellular side of the membrane.

Question 6

What force(s) stabilize(s) the lipid bilayers?

Answer 6

Van der Waals interactions and electrostatic and hydrogen bonding between the polar heads and surrounding water.

Question 7

Which is the proper order of permeability of molecules across a membrane, from the most permeable to the least?

Answer 7

Water, indole, glucose, sodium ion.

Question 8

The fluorescence recovery after photobleaching (FRAP) technique has been used to study:

Answer 8

The lateral diffusion in membranes.

Question 9

Membrane proteins:

Answer 9

Have all of the properties listed.

Question 10

The type of membrane transport that uses ion gradients as the energy source is:

Answer 10

Secondary active transport

Question 11

The specificity of the potassium channel for K+ over Na+ is mainly the result of the:

Answer 11

Differential interaction with the selectivity filter protein.

Question 12

Name some of the features common to all membranes.

Answer 12

1. Membranes are sheetlike structures that are two molecules thick.
2. Membranes are composed of lipids and proteins, both of which may be decorated by carbohydrates.
3. Membrane lipids are amphipathic molecules, composed of hydrophilic and hydrophobic components, that spontaneously form closed bi-molecular sheets in aqueous solutions.
4. Proteins, unique to each membrane, mediate the transfer of molecules and information across the membrane.
5. Membranes are noncovalent assemblies.
6. The leaflets of the membrane bilayers are different; that is the membranes are asymmetric.
7. Membranes are fluid, rather than rigid structures.
8. Membranes are electrically polarized, with the inside of the cell negative with respect to the outside.

Question 13

What conditions are required for a small molecule to spontaneously pass through a membrane?

Answer 13

First, the molecule must be lipophilic, and second, the concentration of the molecule must be greater on one side of the membrane than on the other.

Question 14

Define: Integral Membrane Protein

Answer 14

Interacts tightly with the membrane interior

Question 15

Define: Peripheral Membrane Protein

Answer 15

Interacts with the border of a membrane

Question 16

Define: Channel

Answer 16

Allows rapid movement of molecules down a gradient across a membrane

Question 17

Define: Passive Transport

Answer 17

Facilitated Diffusion

Question 18

Define: Active Transport

Answer 18

Movement across a concentration gradient

Question 19

Define: Na+–K+ ATPase

Answer 19

Inhibited by digitalis

Question 20

Define: Secondary Transporter

Answer 20

Uses the energy of one gradient to create another

Question 21

Define: Antiporter

Answer 21

Molecules moving in opposite directions

Question 22

Define: Symporter

Answer 22

Molecules moving in the same direction

Question 23

Define: Ion Channel

Answer 23

Can be voltage-gated or ligand-gated

Question 24

Arrange the following substances in order of increasing permeability through a lipid bilayer: (a) glucose; (b) glycerol; (c) cl-; (d) indole; (e) tryptophan

Answer 24

Cl-, Glucose, Tryptophan, Glycerol, Indole

Question 25

Differentiate between simple diffusion and facilitated diffusion.

Answer 25

In simple diffusion, the molecule in question can diffuse down its concentration gradient through the membrane. In facilitated diffusion, the molecule is no lipophilic and cannot directly diffuse through the membrane. A channel or carrier is required to facilitate movement down the gradient.

Question 26

Differentiate between passive transport and active transport.

Answer 26

In passive transport (facilitated diffusion), a substance moves down its concentration gradient through a channel or transporter. In active transport, a concentration gradient is generated at the expense of another source of energy, such as they hydrolysis of ATP.

Question 27

Consider Figure 12.20, which illustrates the relation between the sodium-glucose symporter and the Na+–K+ ATPase. If the symporter were inhibited, what effect, if any, would such inhibition have on the ATPase?

Answer 27

Inhibition of the symporter would eventually lead to the inhibition of the ATPase. Because the sodium gradient would not be dissipated by the symporter, the sodium concentration outside the cell would become so great that the hydrolysis of ATP by the ATPase would not provide sufficient energy to pump against such a large gradient.

Question 28

What are two fundamental properties of all ion channels?

Answer 28

1. Selectivity

2. Rapid Transport of Ions

Question 29

True or False:

The sodium-glucose linked transporter does not depend on the hydrolysis of ATP

Answer 29

FALSE
Although the co-transporter does not directly depend on ATP, the formation of the Na+ gradient that powers glucose uptake depends on ATP hydrolysis.

Question 30

Lipid bilayers are self-sealing. If a hole is introduced, the hole is filled in immediately. What is the energy basis of this self-sealing?

Answer 30

The hydrophobic effect. If there is a hole, the hydrophobic tails of the phospholipids will come together, freeing any associated water.

Question 31

Differentiate between peripheral proteins and integral proteins.

Answer 31

Peripheral proteins are attatched to the phospholipid head groups of membrane lipids or the exposed portions of integral membrane proteins. Integral membrane proteins are embedded in the membrane.

Question 32

All biological membranes are asymmetric. What is the energetic basis of this asymmetry?

Answer 32

For both sides of a membrane to become identical, the hydrophilic parts of the lipids, proteins, and carbohydrates would have to pass through the hydrophobic interior of the membrane.

Such movement is energetically unfavorable.