Chapter 12: Membrane Structure and Function Flashcards
Which of the following is TRUE?
- Membranes are lipid bilayers.
- Membrane lipids have both hydrophobic and hydrophilic properties.
- Many membranes are electrically polarized.
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.
C. A bilayer made of lipids with polyunsaturated 16-carbon fatty acids.
Which of the following statements is consistent with the structure of biological membranes?
The membrane lipids self-assemble to form the lipid bilayer
An antiporter and a symporter are examples of:
A secondary transporter
Carbohydrate residues attatched to the membrane lipids are:
Always positioned on the extracellular side of the membrane.
What force(s) stabilize(s) the lipid bilayers?
Van der Waals interactions and electrostatic and hydrogen bonding between the polar heads and surrounding water.
Which is the proper order of permeability of molecules across a membrane, from the most permeable to the least?
Water, indole, glucose, sodium ion.
The fluorescence recovery after photobleaching (FRAP) technique has been used to study:
The lateral diffusion in membranes.
Membrane proteins:
Have all of the properties listed.
The type of membrane transport that uses ion gradients as the energy source is:
Secondary active transport
The specificity of the potassium channel for K+ over Na+ is mainly the result of the:
Differential interaction with the selectivity filter protein.
Name some of the features common to all membranes.
- Membranes are sheetlike structures that are two molecules thick.
- Membranes are composed of lipids and proteins, both of which may be decorated by carbohydrates.
- Membrane lipids are amphipathic molecules, composed of hydrophilic and hydrophobic components, that spontaneously form closed bi-molecular sheets in aqueous solutions.
- Proteins, unique to each membrane, mediate the transfer of molecules and information across the membrane.
- Membranes are noncovalent assemblies.
- The leaflets of the membrane bilayers are different; that is the membranes are asymmetric.
- Membranes are fluid, rather than rigid structures.
- Membranes are electrically polarized, with the inside of the cell negative with respect to the outside.
What conditions are required for a small molecule to spontaneously pass through a membrane?
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.
Define: Integral Membrane Protein
Interacts tightly with the membrane interior
Define: Peripheral Membrane Protein
Interacts with the border of a membrane
Define: Channel
Allows rapid movement of molecules down a gradient across a membrane
Define: Passive Transport
Facilitated Diffusion
Define: Active Transport
Movement across a concentration gradient
Define: Na+–K+ ATPase
Inhibited by digitalis
Define: Secondary Transporter
Uses the energy of one gradient to create another
Define: Antiporter
Molecules moving in opposite directions
Define: Symporter
Molecules moving in the same direction
Define: Ion Channel
Can be voltage-gated or ligand-gated
Arrange the following substances in order of increasing permeability through a lipid bilayer: (a) glucose; (b) glycerol; (c) cl-; (d) indole; (e) tryptophan
Cl-, Glucose, Tryptophan, Glycerol, Indole
Differentiate between simple diffusion and facilitated diffusion.
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.
Differentiate between passive transport and active transport.
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.
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?
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.
What are two fundamental properties of all ion channels?
- Selectivity
2. Rapid Transport of Ions
True or False:
The sodium-glucose linked transporter does not depend on the hydrolysis of ATP
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.
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?
The hydrophobic effect. If there is a hole, the hydrophobic tails of the phospholipids will come together, freeing any associated water.
Differentiate between peripheral proteins and integral proteins.
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.
All biological membranes are asymmetric. What is the energetic basis of this asymmetry?
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.
