Non-EMS/secreted protein - DNA for protein transcribed to MRNA in nucleus - mRNA for protein travels to cytosol - free ribosomes in cytosol begins to translate mRNA to protein - no signal peptide of 8 hydrophobic AA’s translated w/in first approx 20 - translation continues and terminates in cytosol Non-EMS/secreted: ribosomes - DNA for protein transcribed to MRNA in nucleus - mRNA for protein travels to cytosol - free ribosomes in cytosol begins to translate mRNA to protein - no signal peptide of 8 hydrophobic AA’s translated w/in first approx 20 - translation continues and terminates in cytosol - 40s and 60s protein subunits travel separately to nucleolus - completed protein/rRNA 40s and 60s subunits return separately to cytosol - completed protein/rRNA 40s and 60s subunits join together to make functional ribosome when an mRNA is near and in need of a ribosome to translate it Chapter 7: Membrane Structure and Function Membrane Fluidity (defined as movement) 1) Bond type - More (cis) unsaturated bonds-more kinks-increased fluidity 2) Bond length - Longer the phospholipid hydrophobic tail-more interactions that will occur- decrease fluidity
3) Cholesterol - Bulkiness-inserted w/in a membrane will make decrease fluidity Lower temperature – bulkiness… Saturated: Has no double bonds Very tightly packed hydrogens to the carbon skeleton chain No kinks, allows for more flexibility to pack together Most animal fats are saturated – butter Unsaturated: Hydrocarbon chains with cis-double bonds Influence of cis-double bonds in hydrocarbon chains. Double bonds makes it more difficult to pack the chains together, thereby making the lipid bilayer more difficult to freeze. In addition, because the hydrocarbon chains are unsaturated lipids are more spread part, bilayers containing them are thinner Present of bulkiness of cholesterol restricts movement of phospholipids and other molecules- reduces fluidity Low temps – bulkiness of cholesterol disrupts regular packing of hydrocarbon Three Experiments: Fusion of mouse and human cell - Two sets of different colored fluorescent antibodies - One type specific for mouse proteins, another type specific for human proteins - After ~40 mins, we see colors intermixed w/ each other FRAP - Add one color of fluoresce antibodies that are specific to membrane of cell in question - Photo bleach one area for a short period of time - Protein loses fluorescence - This area will gain its fluorescence back FLIP - Add one color of fluorescence antibodies that are specific to the membrane of the cell in question - Photo bleach an area constantly - After a while, will see whole area is white proving cell membrane is fluid, moving Composition of membranes Components:
1) Phospholipids: membrane is used as a barrier for regulation of what goes in and out; serves as a protective barrier; direct relationship between fluidity-permeability (PM with very little unsaturated fat->will have a low permeability); membrane permeability shows how easily molecules can move across membrane; more or less permeable/selective to
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- Fall '09
- Bio Review Sheet