Membrane Fluidity

Question 1

Why is the membrane fluid?

Answer 1

No covalent bonds between lipids

Question 2

What is the fluid mosaic model?

Answer 2

The membrane is a 2D solution of oriented proteins and lipids. Membrane is a mosaic of components that move freely and fluidly in the plane of the membrane

Question 3

What effect do saturated and unsaturated fatty acids have on membrane fluidity?

Answer 3

Unsaturated hydrocarbon tails have kinks that prevent molecules from packing together tightly, enhancing membrane fluidity

Saturated hydrocarbons tails are straight and can pack together tightly, decreasing membrane fluidity

Question 4

What effect does cholesterol have on fluidity?

Answer 4

Acts as a bidirectional regulator of membrane fluidity. It minimises the effects of temperature by expanding the range of temperatures at which a membrane maintains fluidity

Question 5

What is effect of cholesterol at low temperatures?

Answer 5

Increases fluidity by keeping phospholipids from packing together tightly

Question 6

What is effect of cholesterol at high temperatures?

Answer 6

It reduces fluidity by stabilising the membrane and raising the melting point

Question 7

What is effect of cholesterol at normal temperatures?

Answer 7

Decreasing cholesterol would increase membrane fluidity

Question 8

What changes in membrane lipid composition would increase fluidity?

Answer 8

• Decreasing length of fatty acid chains
• Decreasing cholesterol content
• Increasing number of unsaturated bonds in fatty acids

Question 9

What is a ‘lamellar phase’?

Answer 9

Refers generally to packing of polar-headed long chain non-polar tail molecules in an environment of bulk polar liquid, with sheets of bilayers separated by bulk liquid

Question 10

When a membrane is in a ‘lamellar phase’, what phases can it be in?

Answer 10

1. Lamellar liquid crystalline (liquid disorder)
2. Solid gel
3. Liquid-ordered

Question 11

Describe the lamellar liquid crystalline phase

Answer 11

Glycerophospholipids that have unsaturated tails are not well packed so membrane is more fluid

Question 12

Describe solid gel phase

Answer 12

Sphingolipids have long saturated tails and pack more tightly so membrane is less fluid

Question 13

Describe liquid-ordered phase

Answer 13

Presence of cholesterol with lipids with saturated tails (e.g. SM results in lipid ordered raft)

Question 14

Describe fluidity of membrane at cooler temperatures

Answer 14

Straight tails of saturated fatty acids pack tightly –> dense and rigid membrane

Phospholipids with unsaturated fatty acid tails cannot pack tightly due to bent structure of tails –> membrane stays fluid at lower temperatures

Question 15

What allows membranes to be semifluid at room temperature?

Answer 15

A combination of saturated and unsaturated lipids

Question 16

How does frostbite occur?

Answer 16

• Membranes tend to solidify at cold temperatures
• Frostbite occurs when oxygen can no longer diffuse through solidified cell membranes
• After prolonged exposure, outermost cells die