For fusion of a vesicle with its target membrane to
occur, the membranes have to be brought to within 1.5 nm
so that the two bilayers can join (Figure Q13–1). Assum-
ing that the relevant portions of the two membranes at the
fusion site are circular regions 1.5 nm in diameter, calcu-
late the number of water molecules that would remain
between the membranes. (Water is 55.5 M and the volume
of a cylinder is πr2h.) Given that an average phospholipid occupies a membrane surface area of 0.2 nm2, how many
phospholipids would be present in each of the opposing
monolayers at the fusion site? Are there sufficient water
molecules to bind to the hydrophilic head groups of this
number of phospholipids? (It is estimated that 10–12 water
molecules are normally associated with each phospho-
lipid head group at the exposed surface of a membrane.)
![vesicle
target membrane
] 1.5 nm
Figure Q13-1 Close approach of a vesicle and its target membrane
in preparation for fusion (Problem 13-6).](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fb3cc7a06-2183-4e15-85e7-75e9b9cbd156%2Ffbeb3f08-0715-417a-85b2-9f9b769008a7%2F86dffgr_processed.png&w=3840&q=75)
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