Chapter 5Membrane composition and fluidity.

You Must Know

• Why membranes are selectively permeable.

• The structure and function of membrane proteins.

Amphipathic molecules

Fluid Mosaic Model

Figure 5.4-1

Mouse cellHuman cell

Membrane proteins

The Fluidity of Membranes

Membranes must be fluid to work properly; they are usually about as fluid as salad oil.

Figure 5.2

Glyco-protein

Glycolipid

Fibers of extra-cellular matrix (ECM)

Carbohydrate

Cholesterol

Microfilamentsof cytoskeleton

Peripheralproteins Integral

protein

EXTRACELLULARSIDE OF

MEMBRANE

CYTOPLASMIC SIDE OF MEMBRANE

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Figure 5.5

Fluid

Unsaturated tails preventpacking.

Viscous

Saturated tails packtogether.

(a) Unsaturated versus saturated hydrocarbon tails

(b) Cholesterol reducesmembrane fluidity atmoderate temperatures,but at low temperatureshinders solidification.

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Cholesterol

Evolution of Differences in Membrane Lipid Composition

• Bacteria adapted to living in very hot conditions have more saturated fatty acids in their membranes

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• Bacteria adapted to living in very cold conditions have more unsaturated fatty acids in their membranes