W4 - Membrane Lipids Flashcards
Biological membranes are usually 60-100 angstrom thick, describe their polarity, symmetry and fluidity
Polarised (inside cell more -ve than outside), asymmetrical and they’re very fluid (no covalent bonds)
When looking at the bilayer using an EM, why is there banding? (inside of bilayer different to outer edges)
Lipid molecules are amphipathic, EM stain cannot reach the middle of the bilayer due to hydrophobic FAs
The lipids themselves have one function of structure but the membrane has many functions, list these 5 functions
Selective barrier (defence), transport, energy storage, enzymatic reactions and sensing information
What are the 3 main functional groups involved in fatty acids?
Hydrogen, alkyl and carboxyl
What does 18:0 and 18:3 mean when naming fatty acid long chain hydrocarbons?
18 - 18C, 0/3 - no. of C=C
What is the shorthand for octadecanoic, octadecenoic, octadecadienoic and octadecatrienoic acid
18:0, 18:1, 18:2, 18:3
How many C=C do linolenate, arachidonate and laurate have?
Lin - 3, Arach - 4, Laur - 0
If a FA is shorter is the membrane more or less fluid?
More
If a FA has more C=C is the membrane more or less fluid?
More
Thermodynamics always pushes molecules to the lowest energy state, what does this mean when lipids interact?
The lipids dock to form the bilayer as this is the lowest energy state
What are 4 components of phospholipids?
1(+) FA chain(s), glycerol/sphingosine, phosphate and an alcohol attached to the phosphate
The major phospholipids are derived from phosphatidate, what does the ester bond form between when forming a PL?
Phosphate of phosphatidate and hydroxyl of alcohols
Instead of an ester bond, in sphingomyelin there is what bond between the sphingosine backbone and the fatty acid?
Peptide bond
What happens to the primary alcohol in sphingomyelin to join it to phosphorylcholine?
Undergoes an esterification reaction
What are glycolipids?
Sugar containing lipids derived from sphingosine
Glycolipids are asymmetric in terms of where the sugar is, where is the sugar always?
Extracellularly
In glycolipids what is the primary alcohol esterified to?
1 or more sugars
Cholesterol has a steroid nucleus and is not in prokaryotes, how do the molecules associate with the PLs?
Lie parallel to PL, OH interacts with head of PL
Why do PLs and GLs prefer a planar sheet rather than micelles?
The bulkiness of the FA chains makes it unfavourable
What are the main, weak bonds that hold lipids together?
Hydrophobic/van der waals
After glycine in water is added to a layer of phospholipids, what does sonication do?
The waves of pressure disturb the layer of PLs to create liposomes trapping glycine
What is the step after sonification?
Gel filtration to leave the liposomes
What are two things that can be studied by creating liposomes?
Study cell permeability and delivering chemicals to cells
Liposomes are roughly 500A across, how would you make them larger?
Slowly evaporate organic solvent from suspension of PL in a mixed solvent system
Lipid bilayers are highly impermeable to ions and most polar molecules but water is an exception, why?
It’s small, lacks full charges and has very high concentration
Give examples of cells/organelles that have high and low membrane protein content
Myelin cells have low protein content as fairly pure lipids tend to be better insulators, mitochondria has lots of proteins for energy transduction processes
Membrane proteins can be integral and span the membrane but how else may they associate with the membrane?
They can be peripheral
