plasma membrane - skin of lipids w/ embedded proteins covering cells
- protein determines what substances can pass through
- only 2 phospholipids thick
phospholipids - glycerol + 2 fatty acids + phosphorylated alcohol
- normal fatty acids aren't soluble, nonpolar all over
- phosopholipids have polar, organic heads
- forms bilayer sheets so that nonpolar fatty acid tails never touch the water
- phospholipid bilayer - forms spontaneously due to water's tendency to form the max number of hydrogen bonds
- stops any water-soluble substances from passing through
- certain proteins act as passageways through the membrane
fluidity of bilayer - phospholipids have weak interactions w/ each other
- parts of membrane can freely move
- less fluidity where phospholipid tails align close together
- some phospholipids don't align well due to double carbon bonds
- membranes w/ steroid lipids (ex. cholestrol) increase/decrease in fluidity depending on temperature
fluid mosaic model - embedded proteins also have nonpolar parts
- nonpolar parts of phospholipids/proteins come in contact w/ each other; polar parts on the surface
- developed by Singer/Nicolson, disproved the Davson-Danielli model
- phospholipid bilayer - impermeable, flexible matrix
- other parts of the membrane are embedded in it
- nonpolar interior stops polar substances from getting through
- transmembrane proteins - float on/in the membrane
- can move around in the membrane freely
- interior protein network - reinforces the membrane shape
- spectrin links - proteins that give red blood cells their biconcave shape
- anchors some important membrane proteins
- cell surface markers - sugar coating aka glycocalyx
- used as identity markers
- microdomain - distinct areas of the membrane
- plasma membrane not homogeneous
- lipid raft - heavily enriched w/ cholestrol, saturated fats; more tightly packed than surrounding area
examining cell membranes - must prepare specimens before viewing w/ electron microscopy
- epoxy shavings - transparent peelings from a block of tissue embedded in hard matrix
- microtome - machine w/ very sharp blade
- freeze-fracturing - tissue is quick frozen w/ liquid nitrogen
- crack between phospholipid layers form when cracked
- thin coating of platinum used to creat a cast of the surface
membrane proteins - 6 main groups of proteins let cell interact w/ environment
- transporters - allow only certain substances to enter, usually through a channel or on a carrier
- enzymes - certain reactions use proteins in the membrane
- cell surface receptors - detects chemical messages
- cell surface identity markers - ID tag for each cell
- cell adhesion proteins - glue cells to each other (temporary/permanent bonds)
- attachments to cytoskeleton - surface proteins linked to cytoskeleton
membrane protein structure - some proteins anchored in the membrane, others move freely
- anchored proteins connected to phospholipids by molecules w/ nonpolar region and chemical bonding domains that link to the protein
- nonpolar helices/beta-pleated sheets of amino acids keep proteins within the membrane, though polar ends stick out
- single-pass anchors - receptor proteins w/ single-pass anchors
- binds to specific hormones outside the cell
- sends messages into the cell, causing changes inside
- multiple-pass channels/carriers - uses several helices to form a channel
- only way that water-soluble substances can pass into the cell
- pores - beta-pleated sheets forming a barrel to allow water and other substances through
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