Cholesterol

Cholesterol

Fatty acids are in all lipids expect cholesterol.

Cholesterol forms a hydrophobic layer of about 12-20 atoms the optimal belayed has about 6-8nm thickness.

Examples in organisms:

Palmite (16) + sterate (18) unsaturated carbon atoms.

1 double bond                      2 double bond

Linoleate (18) and 3 double bonds, Arcahedonate (20) has 4 double bonds.

Unsaturated fatty acids in membranes are in cis creating beds and kinks so do not pack tightly in membrane. 

Movement of phospholipids within membranes.

-Rotation

-Lateral diffusion

-Transverse diffusion (flip-flop): this is where one monolayer to another and is done by proteins in ER called phospholipids translocations and flippases enzymes.

Lipid membrane is fluid which allows lateral diffusion and move faster than proteins are smaller and weigh less.

Florescence recovery after photo bleaching

1-unlabbled cell surface

2-cell surface molecules labelled with fluoresce dye

3-laser beam bleaches an area of cell surface

4-Florucescent labelled molecules diffuse into bleached area.

Dye creates covalent bond to living cell.

-->Uses a high intensity laser beam

-->Rate of diffusion florescence into bleached area measured over time.

Temperature changes fluidity:

transition temperature (Tm)= Temperature when it melts

Phase transition= Membrane changes state.

Differential scanning calorimetery

-''n''' shaped curve

-Peak is the Tm

-More saturated the higher temperature

saturated fatty acids fit more tightly packed as there are no bends.

Determining fluidity:

-length of fatty acid chains (long chains higher temperature) less fluid.

-Degree of unstauration

Some more in depth information into cholesterol:

-Sterols affect membrane fluidity

-PH group that is polar and everything else hydrophobic

-forms hydrogen bond

-Rigid hydrophobic steroid rings and hydrocarbon chain part interact with adjacent hydrocarbon chain that are adjacent to closest phospholipids head group.

-Plant cholesterol is phytosterols

-Sterol is hopanoids in prokaryotes

-Decrease membrane fluidility above Tm

-Increase membrane fluidilty below Tm

Sterols decrease permeability of lipid bilayer of ions and smaller polar molecules

Pilikotherms (cold blooded animals) cannot regulate own temperature as lipid fluidity decreases as temperature falls membrane would gel. Homotherms (warm blooded) animals compensating effects such as when cold and when you can't feel fingers and toes as sensory never ending stop. When very hot pilikiotherms membranes get very fluid and denature homeoviscous adaptation also is the regulation of membrane fluidility.

Lipid rafts are newly discovered and are localised regions of membrane lipid that are involved in cell signalling. 

**REMEMBER TO STAY POSITIVE LIKE A PROTON!**