Lecture_3_Jan_8_four_slides_per_page_

Lecture_3_Jan_8_four_slides_per_page_ - Lecture 3 Membrane...

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1 Lecture 3 no new reading assignment Membrane lipids properties and packing of lipids major types of lipids in animal cells functions of lipids Functions of lipids structural aspect: permeability barrier of a cell (plasma membrane) r cellular compartments (internal membranes) or cellular compartments (internal membranes) Importance of the permeability barrier of a lipid bilayer xtracellular: high calcium concentration Calcium ion is an important signaling molecule within a cell, and many extracellular signals induce an increase of cytoplasmic calcium concentration. A key reason why calcium ion serves as a major signaling molecule is because a cell has very low cytoplasmic concentration of free calcium ion (compared to the extracellular space or the lumen of ER) at the resting state. sperm endoplasmic reticulum: igh calcium concentration cytoplasmic: low calcium concentration extracellular: high calcium concentration 10000X difference! egg high calcium concentration Such sharp gradient of calcium concentration cannot be maintained if the plasma membrane or endoplasmic reticulum membrane is leaky
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2 calcium concentration is revealed by a Ca2+ sensitive fluorescent dye For example, upon fertilization, there is a rapid increase of cytoplasmic calcium concentration which is essential for embryonic development Importance of the permeability barrier of a lipid bilayer (red color indicates highest calcium concentration, movies 21-3 & 21-4 ) (fluorescence can be used to detect Ca2+, in addition to proteins and lipids) sperm egg Lipids confer the permeability barrier of a membrane cell or organelle membrane leaflet h b h t j t t i d li id it i th For most membranes: 50% protein content For myelin membrane: 25% protein content For mitochondrial inner membrane: 75% protein content Whereas a membrane has two major components, proteins and lipids, it is the lipids which account for the permeability barrier of a membrane (why?) Functions of lipids structural aspect: permeability barrier of a cell (plasma membrane) py ( p ) or cellular compartments (internal membranes) on ructural aspect (esp in signaling): non-structural aspect (esp in signaling): platforms to organize the signaling complex & biosynthetic precursors of signaling molecules Some lipids can form a microdomain on a membrane While the lateral diffusion of lipids occurs readily within one leaflet, the composition of each leaflet is not uniform on the microscopic scale.
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Lecture_3_Jan_8_four_slides_per_page_ - Lecture 3 Membrane...

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