3.19 The metal surface favors a stressed conformation for the dinitrogen
molecule.3.20 Nitrogenase is the enzyme that catalyzes the formation of ammonia
from molecular nitrogen.CHAPTER 4
4.1 Yes.4.2 No.4.3 The presence of the salt stablilizes the water phase, and hence
decreases the freezing temperature, as the enhanced molecular
randomness opposes the tendency to freeze.
4.4 Phospholipids have two or three hydrocarbon chains attached to a
polar head group.4.5 The separation of the molecules into phases. When B >Bidealthe
chemical potential decreases more rapidly than the ideal case and
the system behaves as a good solvent. When B <<0 the chemical
potential decreases less rapidly and the system behaves as a poor
solvent and phase separation occurs. For lipids and detergents, this
phase separation can be in the form of the micelles, bilayers, or other
aggregates.
4.6 In a micelle, the hydrophobic chains are in the interior and the polar
head groups are exposed to the water. A liposome is an aggregate
of lipids or detergent molecules in which the polar surfaces are
exposed to the solvent and the hydrophobic chains are buried in a
bilayer arrangement.4.7 The detergent concentration at which micelles will form.4.8 The tendency for forming micelles would be increased and so the
critical micelle concentration would decrease.4.9 The cubic lipid phase can be thought of as arising from a very high
concentration of liposomes that aggregate into the cubic lipid phase.
4.10Lipid rafts are regions of cell membranes that are rich in certain lipids
and proteins. They have been proposed to play a role in cellular
functions.4.11 The rafts are small and the possibility that the preparation of the
fractionation experiments led to the fractionation cannot be excluded.
4.12 The function of these proteins may be triggered by the formation
of dimers in the raft.ANSWERS TO PROBLEMS 445
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