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Lecture 3

BIOL130 Lecture Notes - Lecture 3: Phospholipid Scramblase, Red Blood Cell, Secretion

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Heidi Engelhardt

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Cell Membranes (Biol 130)
- All membrane lipids are amphipathic (glycolipid, phospholipid, cholesterol)
- Top is always polar (like 4 carbon rings in cholesterol)
- Always spinning
- They happen spontaneously
- What you want in healthy membrane: fluidity- critical for cell survival and function
- If you deease tepeatue, they’ll oe less ad less util the fatty aids gel ad
solidify (not compatible in nature)
- Increasing cholesterol, it will be less fluid (body temperature)
- Can be used for secretory pathway (destined for secretion from inside to outside of cell)
- Scramblase takes random phospholipids from cytosolic side and shifts over to other side
- Enzyme in ER that evens out two layers (important because dragging leaflets to other
- Fresh new phospholipid from ER is incorporate in golgi membrane and another enzyme
expressed in the golgi called flipases selectively flip two across to the other side (PS
and PE)
- Now we have more PS and PE on the other side (cytosolic side)
- Introduced membrane asymmetry
- Scramblase work in ER (even up) but flipases work in Golgi and selectively move 2
- Sugars face out on non-cytosolic space is aspect of asymmetry
- PI is signaling molecule and for it to happen it has to be facing cysotolic space
- Asymmetry is preserved during transport processes
- Beginnings of membrane fusion
Plasma Membrane Model Organism
- Human red blood cell
- Shape is easy to get, suspended (convenient because expiration date)
- No itohodia, o lysosoes, o ER, o uleus…
- Very pure plasma membranes
Membrane Proteins
- What makes membranes functionally distinct
- Anchors: hold cells in relationship to each other and tissues (proteins of extracellular
- Receptors and enzymes: signaling)
Ways proteins can associate with membrane
- Transmembrane
- Monolayer associated
- Lipid linked
- Protein linked
- Secondary structure important to be part of membrane in eukaryotes
- Non polar R groups keep the shape and hold it in the membrane
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