6

Question 1

Lipids:

Answer 1

Lateral diffusion = diffusion in the plane of the monolayer (one circle for 102 s)
Rotation around their vertical axis (10-4 s)
Rotation of the polar head and hydrophobic tail around each single bond
Segmental movements = changes of the angle between single bonds on the hydrophobic chain
Transversal diffusion = 104 - 105 s

Question 2

Proteins:

Answer 2

Lateral diffusion = diffusion in the plane of the monolayer (one cycle for 104 - 107 s)
Rotation around the vertical axis (10-3 s)
Intramolecular movements = vibrations, conformational changes, etc.
Transversal diffusion = forbidden (large molecular weight and size, hydrophilic parts – high energetic barrier)
Lateral diffusion of integral proteins is strongly limited due to associated peripheral proteins and bonds with the cytoskeleton.

Question 3

Conformations of hydrocarbon chains of lipids:

Answer 3

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Question 4

Phase transition in lipid bilayers

Answer 4

All lipids have a characteristic temperature at which they undergo a transition (melt) from the gel to liquid phase.

Question 5

Phase transition temperature (Тс) depends on:

Answer 5

Length of fatty acid chains,
number of double bonds (unsaturated fatty acids), location of double bonds in the chain and charge and polarity of the hydrophilic head.

Question 6

Effects of cholesterol

Answer 6

The phase transition temperature increases slightly depending on the cholesterol concentration. The gel phase system undergoes a transition with increasing amounts of cholesterol from a solid-ordered phase into a liquid-ordered one. Cholesterol stiffens the fluid membranes and softens the gel-to-liquid crystalline phase transition