Chapter 13, Problem 1P

Summary Introduction

To examine: Whether the statement, “In all events involving fusion of a vesicle to a target membrane, the cytosolic leaflets of the vesicle and target bilayers always fuse together, as do the leaflets that are not in contact with the cytosol”, is true or false.

Introduction: There are many protein molecules that are involved in the fusion of vesicle. The vesicle pinches off from the membrane. The pinching-off process brings the two non-cytosolic leaflets of the membrane into close proximity and fuses them, sealing off the forming vesicle.

Answer to Problem 1P

Correct answer: The statement is true.

Explanation of Solution

Phospholipid bilayer is composed of two leaflets (cytosolic and non-cytosolic) of amphipathic lipid molecules whose polar head groups are in contrast with the intracellular or extracellular aqueous phage, whereas the non-polar tails face each other constituting hydrophobic interior of the membrane in the vesicle. The events of fusion of two membranes always begin with the contact and fusion of cytosolic leaflets of the two membrane bilayers. It is followed by the fusion of non-cytosolic leaflets of the cell membranes. The protein domains that face the cytosol always fuse in this manner that help to maintain the topology of the membrane proteins. Thus, fusion of vesicle to a target membrane includes fusion of cytosolic leaflet, followed by non-cytosolic leaflet of vesicle and the target membrane.

Hence, the statement is true.