All of the following statements about the fluid mosaic model of biological membranes are true EXCEPT:Show answer
(A) Lipid molecules in the membrane readily undergo lateral diffusion.
(B) Lipid molecules in the membrane readily undergo transverse (flip-flop) diffusion.
(C) Integral membrane proteins can undergo lateral diffusion.
(D) The saturated hydrocarbon chains of lipid molecules in the membrane undergo carbon-carbon bond rotation.
(E) The transition temperature of a membrane is sensitive to the composition of the lipid molecules in the membrane.
That is rather easy question. To gt right answer, lets consider options one by one.
First, word "readily" was quite unclear, before I looked it up in the dictionary. It means "without hesitation or reluctance", i.e. without doubt, but in our case – rapidly, fast. So A is obviously true, because later (in plane) diffusion is primary characteristic of bilayer.
B is first candidate for right answer, because it is known, that one phohpolipid flip-flop by itself just once a month. But there are special proteins called phospholipid translocators. As wrote in MBoC, they "catalyze the rapid flip-flop of phospholipids from one monolayer to the other".
C is right too, because lots of proteins, e.g. channels and receptors, migrate in plane of bilayer rapidly.
E is true too. There two factors can be selected: saturation and length of phospholipids' tails and cholesterol amount in the bilayer. First two properties shift viscosity curve of membrane, while second smooth it as drawn on the picture below. Transition temperature is – in common sense – temperature when material undergoes phase transition. If tails are saturated (i.e. all carbon-carbon bonds are not double) and long, then it becomes easier to pack such bilayer tightly, thus temperature of freezing shifts to higher value. Contrary, if chains are unsaturated and short, their mobility is lower, thus freezing point will be shifted to lower temperatures. But cholesterol is thing that improve mobility of phospholipids at lower temperatures, as well as keep rigid structure at higher values.
Now, answer D. It is known, that tails of saturated hydrocarbons are very, vary mobile stuff. But they can't get far away from phospholipid core, hence they rotate around some links. Unsaturated phospholipids have double bonds in their tails. That double bonds are actually like two sticks, that connect atoms, so rotation around double bonds is impossible.
So right answer, as we excluded any other, is B and rapid flip-flop, even in presence of phospholipid translocators, doesn't happen.
First, word "readily" was quite unclear, before I looked it up in the dictionary. It means "without hesitation or reluctance", i.e. without doubt, but in our case – rapidly, fast. So A is obviously true, because later (in plane) diffusion is primary characteristic of bilayer.
B is first candidate for right answer, because it is known, that one phohpolipid flip-flop by itself just once a month. But there are special proteins called phospholipid translocators. As wrote in MBoC, they "catalyze the rapid flip-flop of phospholipids from one monolayer to the other".
C is right too, because lots of proteins, e.g. channels and receptors, migrate in plane of bilayer rapidly.
E is true too. There two factors can be selected: saturation and length of phospholipids' tails and cholesterol amount in the bilayer. First two properties shift viscosity curve of membrane, while second smooth it as drawn on the picture below. Transition temperature is – in common sense – temperature when material undergoes phase transition. If tails are saturated (i.e. all carbon-carbon bonds are not double) and long, then it becomes easier to pack such bilayer tightly, thus temperature of freezing shifts to higher value. Contrary, if chains are unsaturated and short, their mobility is lower, thus freezing point will be shifted to lower temperatures. But cholesterol is thing that improve mobility of phospholipids at lower temperatures, as well as keep rigid structure at higher values.
So right answer, as we excluded any other, is B and rapid flip-flop, even in presence of phospholipid translocators, doesn't happen.
