Chapter 5Membrane composition and fluidity.

You Must Know

• Why membranes are selectively permeable.

• The structure and function of membrane proteins.

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.

Amphipathic molecules

Fluid Mosaic Model

Figure 5.2

Glyco-protein Glycolipid

Fibers of extra-cellular matrix (ECM)

Carbohydrate

Cholesterol

Microfilamentsof cytoskeleton

Peripheralproteins

EXTRACELLULARSIDE OF

MEMBRANE

CYTOPLASMIC SIDE OF MEMBRANE

Integralprotein

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Which of the amino acids below would you be more likely to find in section “A” of the protein?

Integralprotein

A

Which of the amino acids below would you be more likely to find in section “B” of the protein?

Integralprotein

B

Figure 5.5

Fluid

Unsaturated tails preventpacking.

Viscous

Saturated tails packtogether.

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

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Cholesterol

Evolution of Differences in Membrane Lipid Composition

Would bacteria adapted to living in very hot conditions have more saturated or unsaturated fatty acids in their membranes?

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Unsaturated tails Saturated tails

Evolution of Differences in Membrane Lipid Composition

• Would bacteria adapted to living in very cold conditions have more saturated or unsaturated fatty acids in their membranes?

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Unsaturated tails Saturated tails

Evolution of Differences in Membrane Lipid Composition

The ability to change the lipid compositions in response to temperature changes has evolved in organisms that live where temperatures vary.

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