Deck 10: Lipids, Membranes, and Cellular Transport

Question 1

Mediated transport or diffusion will ultimately result in the concentration of diffusing substance being the same on both sides of the membrane.

Answer 1

False

Question 2

Which of the following is NOT relevant to facilitated transport across biological membranes?

A) An ionophore is a carrier protein that increases the permeability of a membrane to ions.
B) Some permeases can transport their substrates in both directions.
C) A symport will transport two molecules in the same direction across a membrane.
D) ATP hydrolysis is required.
E) An antiport will move substrates in opposite directions across a membrane.

Answer 2

D

Question 3

Lipid rafts are small long-lived structures that respond to stimuli to transiently associate with each other to form larger raft platforms.

Answer 3

False

Question 4

Linolenic acid has cis double bonds with the formula CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH. Write out the abbreviated systematic numbering for this fatty acid.

Question 5

Passive facilitated cotransport can move some substrate across a membrane against its concentration gradient.

Question 6

The rate of nonmediated diffusion tends to increase as the ________ character of the diffusing substance increases.

Question 7

Digitoxin can act as a short term cardiac stimulant by inhibiting the Na+-K+ pump.

Question 8

Which of the following is unlikely to be a characteristic of a membrane protein?

A) Largely hydrophobic transmembrane segments
B) α-helical membrane-spanning motifs.
C) Covalently attached lipid moities
D) Symmetric orientation across the membrane
E) β-sheet membrane-spanning motifs

Question 9

Integral membrane proteins can be inserted into the membrane and folded into the normal 3D structure during translation.

Question 10

Raft platforms in membranes have functional roles in cell signaling and sorting of proteins into specific ________ in the cell.

Question 11

Which of the following statements is FALSE?

A) The longer the chain length of a saturated fatty acid, the higher the melting temperature.
B) The difference in melting temperature between a saturated fatty acid and an unsaturated fatty acid with the same chain length is only a few degrees C.
C) Most types of fat in many animals is used in energy production.
D) Some unsaturated fatty acids are liquid at physiological temperatures.
E) Fatty acids exist in the anionic form (RCOO-) at physiological pH.

Question 12

Which of the following statements about biological membranes is FALSE?

A) They are composed of a mixture of lipids and proteins in which lateral diffusion of components is possible.
B) Lipids and proteins move laterally at approximately the same rate within the membrane.
C) The faces of biological membranes are distinct and usually different in both composition and structure.
D) Phospholipids often require a specialized enzyme to facilitate movement across (flipping) the membrane.
E) They are often organized into smaller regions of specific function.

Question 13

In an aqueous environment the hydrocarbon tails of lipids tend to associate by entropy-driven ________ and by Van der Waals interactions.

Question 14

Which of following lipids can be a major component of biological membranes?

A) Phosphatidic acid
B) Phosphatidylcholine
C) Phosphatidylinositol
D) Cholesterol
E) B and D

Question 15

Saturated fatty acids are different to unsaturated fatty acids because they:

A) have an even number of carbon atoms.
B) have short hydrophobic tails.
C) have no C=C double bonds.
D) exhibit free rotation about the carbon carbon bonds in the hydrocarbon tail.
E) mostly have cis double bonds.

Question 16

The standard free energy that is required for the sodium-potassium ATPase to pump two K+ ions into the cell and three Na+ ions is +43.8 kJ/mol but the standard free energy change of hydrolysis of ATP is only -32 kJ/mol. This apparent imbalance of free energy can be accounted for because:

A) the movement of Na+ ions is down the concentration gradient.
B) the movement of K+ ions is down the concentration gradient.
C) the membrane potential favours the flow of ions.
D) more than one ATP is hydrolyzed.
E) the free energy provided from the hydrolysis of one ATP is sufficient under physiological conditions.

Question 17

Sphingomyelin contains a fatty acid linked by an ________ bond and phosphocholine linked via the C-3 hydroxyl group of sphingosine.

Question 18

Which of the following mechanisms is responsible for the selectivity of aquaporins for water?

A) Size exclusion
B) Electrostatic repulsion
C) Dynamic hydrogen bonding
D) Prevention of ion gradient formation
E) All of the above

Question 19

The sodium-glucose cotransport system is an example of:

A) an antiport transporter.
B) passive transport.
C) facilitated transport.
D) an ATP-dependent transporter.
E) none of the above.

Question 20

Active transport can move a substance across a membrane ________ its concentration gradient.

Question 21

Action potentials are propagated along a nerve axon by sequentially opening and closing a series of voltage-gated potassium and sodium channels.

Question 22

The Na+-K+ ATPase uses the free energy of ATP hydrolysis in an active transport process to move Na+ and K+ across a membrane. What would the rate of nonmediated transport be given that the permeability coefficient for K+ through a human erythrocyte membrane is 2.4 × 10-10 cm/s. K+ ions must be moved from a concentration of 4 mM on the outside of the cell to 155 mM inside the cell?