Lipids, Membranes & Permeability

Saturated fatty acid

Contains no C=C double bonds.

Unsaturated fatty acid

Contains one or more C=C double bonds.

What does a cis double bond do to a fatty-acid tail?

Creates a kink.

Triglyceride

Glycerol attached to three fatty acids.

Main function of triglycerides

Energy storage.

Phospholipid

Amphipathic lipid with polar head and two hydrophobic tails.

Amphipathic

Has both hydrophilic and hydrophobic regions.

Phospholipid head

Hydrophilic/polar.

Phospholipid tails

Hydrophobic/nonpolar.

Why do phospholipids form bilayers in water?

Heads face water while tails cluster away from water.

What type of lipid does Dunn associate with micelles?

Cone-shaped lipids with one fatty tail.

What type of lipid favors bilayers?

Two-tailed phospholipids.

Steroid

Lipid containing four connected carbon rings.

Cholesterol

Steroid component of animal membranes.

What is the membrane's hydrophobic core?

The nonpolar fatty-acid tails.

What crosses the bilayer most easily?

Small nonpolar molecules.

Why don't ions freely cross the bilayer?

Charge is unfavorable in the hydrophobic core.

Do large polar molecules cross easily by simple diffusion?

No.

How can you recognize a triglyceride?

Glycerol attached to three fatty-acid chains.

How can you recognize a phospholipid?

Polar phosphate-containing head plus hydrophobic tails.

How can you recognize a steroid?

Four fused carbon rings.