BCOR 103 1st Edition Lecture 4 Outline of Last Lecture I II III IV Amino Acids The Peptide Bond Levels of Protein Structure Protein Alterations Outline of Current Lecture I II III IV Introduction to the Cell Membrane Cell Membrane Lipids Cell Membrane Proteins The Fluid Mosaic Model Current Lecture Cell membranes are selective barriers meaning that there is a process by which things are allowed to pass in and out of the membrane There are many different roles that a cell membrane can play within cell biology First cell membranes keep organelles contained within the space of the cell so that they do not mix with the environment that they are in or with other cells Cell membranes also provide protection to the cell and allow the outside environment to interact with the cell Membranes can provide a barrier between concentration gradients and retain certain biochemical to the spaces that they need to be Energy can also be stored within a cell membrane The basic anatomy of a phospholipid includes a polar hydrophilic head group and nonpolar hydrophobic tails Depending on the type of phospholipid the different types of head groups can be made up of choline serine ethanolamine or inositol When phospholipids arrange themselves they typically make a phospholipid bilayer In this arrangement the tails will come together to create a waterless environment and the heads will be exposed to an aqueous environment For a bilayer they will arrange in two layers from top to bottom it is head group tail group tail group head group One exception would be a micelle which is when the phospholipids arrange in a single layered sphere There are three classes of proteins typically associated with cell membranes integral membrane proteins peripheral membrane proteins and lipid linked proteins Integral membrane proteins are embedded within the membrane and protrude on either side of the membrane Examples of integral membrane proteins are receptors or transporters Peripheral membrane proteins link to the head groups of phospholipids on the outside of the membrane They do not typically interact with the hydrophobic portions of phospholipids Lipid linked These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute proteins hang from the membrane with one end attaching to the fatty acid tails of the phospholipids within the membrane A few subclasses of proteins include seven spanning proteins which are seven alpha helices linked together within the membrane Often seven spanning proteins or serpentine proteins are hormone receptors Seven spanning proteins are an example of integral proteins Another example of integral proteins is amphipathic tunnel proteins Amphipathic tunnel proteins are a collection of alpha helices usually four or more that arrange themselves to have the hydrophobic portions of the cylinders next to the tails of the phospholipids and the hydrophilic portions of the cylinders making a channel that molecules can pass through Amphipathic means the structure contains both hydrophilic and hydrophobic portions The third subclass of integral proteins is beta barrel proteins Beta barrel proteins are quite similar to amphipathic tunnel proteins They differ in that beta barrel proteins are composed of betapleated sheets that align to form a larger channel or pore Recall that beta pleated sheets are a secondary structure of proteins The cell membrane is a fluid mosaic model The phospholipids align in a bilayer and the bilayer itself effectively floats on the cytoplasm The fluidity is regulated by three factors the length of the fatty acid tails the steroid content within the membrane and how many fatty acid tails are unsaturated The less saturated the membrane the more fluid it is Lipids are able to move within the membrane they are not fixed in one place Some phospholipids are immobile because they are tied to the cytoskeleton however most can move freely