Lipids & membranes Flashcards
Give three roles of membranes
Form the boundaries around the cell and its sub compartments
Act as selectively permeable barriers
Contain receptors
Generate chemical and electrical signals
Are the surfaces on which metabolic reactions can occur
Give the three major types of membrane lipids
glycerophospholipids, sphingolipids, sterols (typified by cholesterol)
What are glycerolphospholipids derived from?
Glycerol-3-phosphate
What is the basic structure of a glycerolphospholipid?
AA 3 carbon backbone, two fatty acid groups attached to carbons one and 2 by ester bonds, a phosphate group with a specific head group on carbon 3
What causes the kink in a fatty acid?
A double bond in the hydrocarbon chain
What are the key components of a sphingolipid?
Have a sphingosine molecule as their backbone (not a glycerol like phospholipids), a fatty acid chain and a choline head group.
What are gangliosides?
A family of membrane sphingolipids that are particularly abundant in the brain
What does cholesterol consist of?
A fused ring structure with an aliphatic chain (which folds up to form a rigid, compact structure)
Define amphipathic
Lipids both have a hydrophobic part and a hydrophilic part
What makes lipids form a bilayer? What is this effect called?
It is entirely spontaneous, driven by the desire to get the hydrophobic parts as far away from the surrounding water as possible
This is called the hydrophobic effect
Name 3 forces that maintain the lipid bilayer structure
hydrophobic interactions, van der waals forces between hydrocarbon tails, charged bonds, H bonds between polar head groups and water
Who discovered the fluid mosaic model?
Singer and Nicholson 1972
How can lipids move in the bilayer?
Rotate on their axes or move laterally along the side of the membrane
What is each surface of the bilayer known as?
The leaflet
What are lipid rafts?
Parts of the membrane where some lipids and proteins cluster; have special functions
Do vesicles have the same structure as a lipid bilayer?
yes
Why does the membrane have fluidity?
There are no covalent bonds between lipids. They can rotate on their axis or move laterally sideways
Why do lipids not readily flip from one side of the bilayer to the other?
It is energetically unfavourable - the hydrophilic head group would have to be moved across the hydrophobic interior
What is the name of the process of lipids flipping from one side of the membrane to the other?
Transverse diffusion
How do lipids get put on the correct leaflet when it is assembled?
Enzymes
Give 3 factors that influence the fluidity of the membrane and explain why
Heat - more energy means they will move faster
Increasing length of fatty acid chains - decrease in fluidity because there will be more hydrophobic interactions between chains
Increasing the number of unsaturated double bonds - increases fluidity because these double bonds are in the cis formation, causing a kink which disrupts the neat packing
More cholesterol - less fluidity because it adds stability
Why is the membrane semi-fluid at room temp?
A combination of saturated and unsaturated lipids
Why does frostbite occur?
Membrane solidifies at cold temperatures - frostbite occurs when oxygen can no longer diffuse through solidified membranes. The coldest, outermost cells die.
Why do reindeer not get frostbite?
They have a different chemical structure with a high percentage of unsaturated lipids so the membranes stay fluid at low temps and oxygen can diffuse through for cell metabolism.
