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18 Cards in this Set

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What is the cell bilayer made of?

50% by mass protein


50% by mass phospholipids



what is the supporting evidence for the lipid bilayer?

1. xray diffraction (shows denser areas outside and less dense inside then dense again on the other side)


2. Transmission EM: osmium stain shows the same thing as x ray diffraction: stained outside of cells to show outer layer


3. freeze fracture em splits along bilayer

what are the 3 types of lipids?

1. phospholipids


2. glycolipids


3. cholesterol

what does amphipathic mean?

all have polar and non-polar parts

what are two shapes groups of lipids form and why?

1. single tail lipids form micelle , or like a cone


2. double tail lipids form bilayer




bilayers are more energetically favorable than single layers

What did the ESR experiment prove?


1. phospholipids can spin and rotate


2. they rarely flip to the otherside of the bilayer

what is the "transition temperature"?

the temperature where phospholipids transition from gel-like to fluid phase

what is the structure of a phospholipid?

1. polar head group


2. backbone


3. fatty acid chain(s)



how does fluidity change by type?

if the tails are saturated fatty acids, they will link together with non-covalent bonds and be less fluid. If the tails are longer, they will also have more interactions and be less fluid




if they are unsaturated, they will be more fluid because they don't link together as easily

What do cells want from their barrier? why?

1. Constant fluidity


2. constant permeability


3. constant barrier




because proteins and enzymes need constant conditions in order to work properly

what are the four main phospholipids and where are they located on the membrane?


what is the minor phospholipid and why is it important?

1. phosphatidyl ethanolamine : primarily internal


2. phosphatidyl serine: primarily internal


3. phosphatidyl choline: primarily external


4. sphingo-myelin: primarily external


5. Phosphatidyl inositol is minor, important for signaling

Where are phospholipids made? what are the components?

cytoplasmic side of the ER bilayer




2 fatty acids and glycerol 3-phosphate

How are phospholipids put on the outside part of the bilayer if there's no flipping?

there are translocation proteins or "flippases"!
1. flip phospholipids across bilayer


2. are head group specific

what is a "scramblase" and how does it work?

when a cell dies, there's a calcium influx. This turns on the scramblase which randomizes which phospholipids are where on the bilayer.




phosphatidyl serine on the outside signals a macrophage to come eat the dead cell

How do other organelles get their lipids?

1. ER is connected to nuclear membrane


2. vesicles carry lipids ER> golgi> lysosomes + plasma membrane


3. for mitochondria and chloroplasts, there are phospholipid exchange proteins that carry from ER to the organelles


4. some may transfer when organelles touch

what is a lipid raft? why are they important?

a bunch of lipids stay together and have a collection of proteins and signalling molecules. they move together throughout the bilayer

what is FRAP?

fluorescence recovery after photobleaching:


it bleaches an area and if fluorescence recovers it means that proteins moved to that area