membrane structures

Phospholipids

Abundant in biological membranes

What are phospholipids constructed of

Fatty acids, glycerol scaffold, phosphate, alcohol

How is the alcohol joined to the phosphate?

The hydroxyl group is joined by an water linkage to the phosphate

Common alcohol components of phospholipids

Serine, inositol, ethanolamine, choline, glycerol

Phosphoglycerides

Phospholipids with a glycerol scaffold

Sphingolipids

Phospholipids built on a sphingosine scaffold

Where are the fatty acids, phosphate, and alcohol attached on sphingosine

Fatty acids on the NH3+ and phosphate + alcohol on the OH

Glycolipids

Sugar containing lipids with a sphingosine scaffold (instead of phosphate)

Steroids

Hormones and membrane lipids

Cholesterol

A sterol (steroid + alcohol)

What drives formation of bilayers in aqueous solutions?

Hydrophobic effect

What forces are between the hydrocarbon tails

Van der waals

What attractions are between polar head groups and water?

Hydrogen bonding and electrostatic interactions

Membrane fluidity influenced by

Length of hydrocarbon chains, saturation, temperature, cholesterol

Membrane at low temperature

Gel like consistency and low fluidity. Liquid ordered state

Membranes at high temperatures

Liquid disordered state and more fluidity

How does cholesterol help membrane fluidity at high temps?

Fills gaps created by unsaturated fatty acids to form specific complexes between cholesterol and phospholipids which decreases fluidity

How does cholesterol help membrane fluidity at low temps?

It can disrupt packing between saturated fatty acids which helps increase fluidity

Uncatalyzed transbilayer (flip flop) diffusion

Very slow and requires enzyme to speed up process

Uncatalyzed lateral diffusion

Very fast

Permeability of membranes

Low permeability for ions and large polar molecules. Small polar and small nonpolar can pass through

Why can’t ions cross a membrane?

Surrounded by shells of water molecules and wouldn’t be able to cross hydrophobic tails. Removing shell would be too unfavourable

Lipid nanoparticles to deliver mRNA vaccines

-ve charge of DNA stabilized by +ve charge of phospholipids that provide a protective environment for mRNA and can be injected into body and translated