Question

1. What biochemical feature of a phospholipid molecule allows phospholipids to spontaneously form closed compartments when placed in an aqueous solution?

a) they are amphipathic

b) they are charged

c) they are spherical

d) they have a single fatty acid tail

2. Other than phospholipids, what molecule do cells use to alter the fluidity of biological membranes?

3. What distinguishes active transport from passive transport?

a) active transport can utilize channel proteins

b) passive transport does not utilize carrier/transporter proteins

c) active transport requires the input of energy

d) active transport only occurs at the plasma membrane

4. In the case of active transport, the Na+/K+ pump undergoes a sequence of conformational changes that allows the movement of Na+ and K+ across a membrane against their electrochemical gradients, while in the case of ER protein import SRP undergoes a sequence of conformational changes to allow the signal sequence to interact with the translocation pore. What drives these conformational changes?

a) hydrolysis of a high energy phosphate bond

b) binding of a solute or protein

c) both

d) neither

5. Is protein import into the ER co-transcriptional, or co-translational?

Answer 1

1) The correct answer is a) they are amphipathic. Phospholipid molecules have hydrophobic and hydrophilic regions. when these are placed in a aqueous solution, hydrophobic regions buried inside and hydrophilic regions exposed to the water. This facilitates formation of closed compartments.

2) The correct answer is cholesterol. Cells use cholesterol to regulate fluidity of membranes. Cholesterol acts as a regulator at higher and lower temperatures to maintain fluidity of membranes.

3) The correct answer is c) active transport requires input of energy. Passive transport doesnot require energy.

4) The correct answer is c) both. Hydrolysis of high energy phosphate bond and binding of solute or protein drive these conformational changes. In case of Na+/K+ pump, ATP hydrolysis and binding of Magnesium ions drive conformational changes. In case of SRP, binding of SRP to signal peptide and GTP hydrolysis drive conformational changes.

5) The correct answer is co-translational. Protein import into the ER is co-translational.