What are lipids?
- Water-insoluble (hydrophobic) molecules made of hydrocarbons
What are biological lipids?
- Triglycerides (triacylglycerols): energy storage
- Phospholipids: component of cell membrane
- Sterols: component of cell membrane
What are fatty acids?
- Hydrocarbons with a carboxyl group at one end
- Building blocks of triglycerides and phospholipids
How do fatty acids vary?
- # of carbons in hydrocarbon/chain length
- Presence and number of carbon-to-carbon double bonds
What is a saturated fatty acid?
Has no carbon-carbon double bond, straight, and tightly compact
What is an unsaturated fatty acid?
Has one or more carbon double bonds (cis double cond), creating bends; preventing a tightly compact structure
What is an unnatural unsaturated fatty acid?
Has one or more carbon double bonds (cis double cond), but does not create bends
What is a Triglyceride?
- An energy storage molecule
- 3 fatty acid “tails” bound to a glycerol anchor
What is a Phospholipid?
Head group:
- Organic molecules
- Phosphate
- Glycerol
Attached to 2 fatty acid tails
What is an amphipathic molecule and give an example
- Contains a hydrophobic end and hydrophilic head
e.g.
Phospholipid
What do phospholipids spontaneously form in water?
- Bilayers
- Head groups facing out with tails pointing toward each other
How is the lipid bilayer fluid?
- Most phospholipid molecules are independent (not attached, free to move along the plane of the membrane)
How do you increase membrane fluidity?
- Increase temperature, unsaturated fatty acids (few van der Waals interactions, shorter chain length of fatty acid
What regulates membrane fluidity?
Sterols
How do sterols regulate membrane fluidity?
Animal cells insert cholesterol into the bilayer which
- Prevent excess viscosity by stopping the phospholipids from packing too tightly together
- Prevent excess fluidity by filling gaps between phospholipids
How does membrane fluidity affect the permeability of the membrane?
- Fluid membranes are leaky: more solutes can pass across the bilayer quickly
- Viscous membranes are better barriers: fewer solutes can cross the membrane more slowly
Lipid bilayers have selective permeability, name the least diffusible to most diffusible molecules
- Ions (least)
- Large uncharged polar molecules
- Small uncharged polar molecules
- Non-polar molecules (most)
How can proteins span a membrane?
When a protein spans a membrane, it can form a channel that allows specific molecules, like ions or water, to flow through the membrane, facilitating their movement in and out of the cell.
e.g.
Aquapourin forms a channel to allow water through
What is diffusion?
- Tendency of dissolved molecules to evenly distribute themselves in a solution
- High-concentration to low-concentration
- Equilibrium will eventually be reached (concentration gradient is eliminated)
Diffusion works across membranes if…
The solute is free to pass through the bilayer
What is osmosis?
Diffusion of water
When does osmosis occur?
If the solute cannot move, then the water will move from low solute concentration to high solute concentration
What is Tonicity?
The ability of a solution to affect the shape and movement of water in and out of cells, based on the concentration of solutes in the solution compared to the inside of the cell
What are hypotonic conditions?
- Lower concentration of solutes outside the cell, and higher concentration of solutes inside the cell
- Water flows into the cell
