Week 1 Class Notes and Chapter 1 Notes
Week 1 Class Notes and Chapter 1 Notes BIOL 4610
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This 9 page Class Notes was uploaded by Luke Holden on Sunday August 28, 2016. The Class Notes belongs to BIOL 4610 at Clemson University taught by Susan Chapman in Fall 2016. Since its upload, it has received 80 views.
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Date Created: 08/28/16
Week One Book and Lecture Notes Combined Chapter 1 Membranes + Lectures (8/168/25) Roles of membranes Define the boundaries of the cell and its organelles Sites for specific biochemical functions Regulate substance movement across membranes Extracellular signaling Cell to cell contact and adhesion o Defining the boundaries Goal: Keep the good in and the bad out Terminology associated with boundaries For the plasma membrane: o Inner bilayer: cytoplasmic face o Outer bilayer: exoplasmic/extracellular face For the golgi: o Inner bilayer: lumnar face o Outer bilayer: cytoplasmic face Nucleus and the mitochondrion have double bilayers o Specific function= specific proteins good way to characterize membranes the glycoproteins of the heart cells are different than that of the small intestine This is an identification system much like a place of business would have o Regulation of substances: involving transport proteins o Detect and Transmit membranes take part in signal transduction mechanisms used to transmit signals o Cell adhesion and contact adhesive: junction mediated by cadhedrins tight junctions forms seal to prevent fluid from passing through gap junction (the bridge) bridge across animal cells (plasmodesmata) for plant cells) that allows items to be brought back and forth across the cell. Structure of membranes o The Fluid part of the fluid mosaic Membrane lipids have 3 major classes Phospholipids o This is the most abundant type of lipid found in the cell membrane o Phospholipids have three main components Polar head group (this can vary) (don’t need to know the structures just the names of the head groups) Ethanolamine neutral Choline neutral Serine(1) Inositol(1) Glycerol(1) A negative phosphate back bone 2 fatty acid chains that are attached to the 1 and 2 oxygen spots on the glycerol Fatty acid chains can either be saturated (no double bonds= no kinks) or unsaturated (1 or more double bonds= kinks) o PHOSPHOLIPIDS ARE: AMPHIPATHIC They are both hydrophobic and hydrophilic Hydrophobic= lypophilic= water hating= fat loving Hydrophilic= lypophobic= water loving= fat hating THIS IS CRITICAL NOT ONLY TO THE MATERIAL ON THE EXAM BUT TO THE STRUCTURE AND THE FUNCTION OF THE MEMBRANE AS WELL o Different classes of phospholipids in the membrane: Phosphoglycerol lipids Phosphosphingolipids Most abundant in the membrane Already has an fatty acid attached Can also be called phosphoglycerides Way to tell: The sphingoseine has an amide bond and a fatty acid that is already attached to sphingoseine molecule. Glycolipids: These are very similar to phospholipids (amphipathic) except it does not have a phosphate or a polar head group. In fact in is just a glycerol or sphingosphine backbone with the attachment of a monosaccharide instead of the phosphate. o o common glycolipids: cerebrosides: has a single uncharged sugar head group ganalgiosides: has one ogliosaccaride (many sugars) and 1 or more negative head groups o Functions of glycolipids: They are specific to certain membranes of different parts of the cell so they serve as an identification system for the cell This is also the identification system of some viruses and cells which the immune system can use to identify. This is also a way to identify your blood type O antigen is the universal donor and AB is the universal Recipient A type cannot give to B and B cannot give to A Group A – has only the A antigen on red cells (and B antibody in the plasma) Group B – has only the B antigen on red cells (and A antibody in the plasma) Group AB – has both A and B antigens on red cells (but neither A nor B antibody in the plasma) Group O – has neither A nor B antigens on red cells (but both A and B antibody are in the plasma) (redcrossblood.org) Sterols These are a four ringed rigid and planar structure that is found in varying concentration through the cell membrane amphipatic as well It is very important that you have enough cholesterol in your diet or otherwise you will die Functions of sterols: o They are a fluidity buffer Because sterols are rigid they provide a fluidity buffer for the cell membrane due to varying temperatures During high temperatures, they keep the phospholipids from separating and osmotic lysis from occurring During low temperatures, cholesterol keeps the membrane from forming a solid like consistency because its structure does not compress. Phytosterol in plants= cholesterol in animals gosterol= cholesterol in fungi Membrane Fluidity All membranes require an optimum fluidity in order to function T –m ransition temperature for the membrane of the cell Important relationships to remember: Increase the saturation= Increase T m Increase the unsaturation= Decrease T m Generally : Increase the fatty acid chain length= Increase m Trans double bonds= Increase T m Cis double bonds = Decrease T m Sterols on membrane fluidity: o Cholesterol decreases fluidity in high temps o Cholesterol increases fluidity in low temps o Orients itself by using the hydroxyl group to orient itself within the membrane by bonding to the polar head group o Cholesterol also so plugs small holes and channels that would be susceptible to other small particles Regulation of membrane fluidity: o Changing the lipid composition is called homeovicous adaptation o This is very important for cold blooded animals and small organisms o Decrease the fatty acid chain you must be living in colder temperatures Lipid Rafts: o regions on the membrane that are involved in cell signaling o dynamic heterogenic monolayers for membranes o Composed of: increased cholesterol, Therefore increased rigidity glycoshpingolipids, therefore increased tail length saturated lipids therefore increased packing o Why? Allows for faster cell signaling due to rafts being able to move about the membrane and then align. By aligning, then the signal can be transmitted to the inside of the cell The Mosaic part of the fluid mosaic model Proteins are all throughout the cell membrane o There are three main classes of proteins: integral Proteins prephrial proteins GPI anchored proteins Integral Proteins Characteristics o Remain in the lipid bilayer by hydrophobic interactions o Amphipathic o Difficult to isolate o monotropic sticks out on one side o transmembrane sticks out on both ends Single pass double pass multi subunit o anchored to the lipid bilayer by one or more hydrophobic membrane segments o 2030 AA long in alpha helix conformation o Beta barrels Antiparallel hydrophobic on the outside hydrophilic on the inside o Porins channels that only allow specific molecules to go through (special entrance) Glycophorin carbohydrates are tightly covalently bonded to the protein Sugars attract water so water comes to the sugar and can form a gel like substance in particular around the ovum o Albumen egg white of the chicken egg o Albumin human ovum Can attract other glycophorins to form a dimer that is a channel. Bacteriorhodopsin type of porin in bacteria that absorbs photons of light in order to change conformation to allow protons out of the cell can also be called a proton pump Peripheral Proteins on the exoplasmic surface held on by weak electrostatic forces and hydrogen bonding These are the easiest to remove They mainly bro out on the outside of the cell waiting to be accompanied by a special molecule There is not enough room on the inside of the cell for the proteins to hang out. LipidAnchored Membrane Proteins polypeptide chains of lipidanchored membrane proteins are located on the surfaces of membranes covalently bound super hard to remove Strong detergents are required proteins bound to the inner surface of the plasma membrane are linked to fatty acids or isoprynel groups Types of LipidAnchored Membrane Proteins: o Fatty acidanchored membrane proteins: attached to saturated fatty acid usually myristic acid (14C) or palmitic acid (16C) o Isoprenylated membrane proteins: made in the cytosol and then modified by addition of multiple isoprenyl groups (5C) usually farnesyl (15C) or geranylgeranyl (20C) groups o GPIanchored membrane proteins are covalently linked to glycosylphosphatidylinositol Types of anchoring: o aceylation: saturated lipid o prenylation : highly unsaturated lipid Detergents and membranes: o Peripheral membrane proteins are usually easy to isolate by changing pH or ionic strength o Chelating (cationbinding) agents are also used to solubilize peripheral membrane proteins o Lipidanchored proteins are isolated by same thing and strong detergents o Integral membrane proteins are difficult to isolate from membranes o Often detergents are used that disrupt hydrophobic interactions and dissolve the lipid bilayer o Ionic detergents: SDS and Sodiumdeoxycholate o Nonionic detergents : Triton x100 and octyloglucoside o Micelles: Critical micelles concentration (CMC) concentration of micelles required to remove a protein conc > CMC = complete micelle formation and possible degradation of the protein conc< CMC = no complete micelle formation
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