Summary of Chapter 7: Cell MembranesWhat is a cell membrane?A cell membrane is a protective outer layer in a cell. It allows certain items to enter and other cannot, this makes it semi-permeable. What makes up a membrane?- Phospholipid bilayer- Proteins- Carbohydrates- CholesterolFluid Mosaic ModelThe cell membrane is sometimes referred to as the fluid mosaic model because the lipids, proteins, and other molecules make each membrane unique from one another. The lipids and proteins can move within the membrane by spinning, swaying and sometimes even flipping. A few factors effecting the fluidity of the membrane are length of fatty acid tails, presence of double bonds in tails, and the presence cholesterol. When the phospholipids have shorter tails they are less likely to interact therefore the membrane is more fluid because they won’t get tangled. When double bonds are present, they create a kink in the fatty acid tail causing the membrane to be more unsaturated meaning more fluid! When cholesterol is present it tends to stabilize and stack up in the membrane making it less fluid.Types of ProteinsThroughout the membrane there are a variety of proteins these include integral and peripheral proteins. The integral proteins can either be transmembrane meaning the protein goes through the entire membrane. Or it can be Non-transmembrane where it is in the membrane but does not go through the whole membrane. Whereas peripheral proteins lay on the side of the membrane and do notenter it at all. The purpose of these proteins are transport, enzymatic activity, signal transduction, cell to cell recognition, intercellular joining, attachment to cytoskeleton and ECM. There are two types of transport proteins, there are channels and carriers. Channels provide a passageway for the direct diffusion of ions or small polar molecules across the membrane. Carriers also transport these ions and small polar molecules but they do this through conformation change which is similar to a lock and key fit.Only one side of the protein is open at a time to get the molecule across the membrane. There are 3 types of carriers. The first type is a Uniporter which can take a single molecule one direction. A Symporter can take two or more in the same direction. Lastly there is the Antiporter, which transports two or more molecules in the opposite direction.Types of TransportThere are three major types of transportation. There is passive, active, and bulk. In passive transportation there is no required energy. Within passive there is passive diffusion, which consists of small, nonpolar molecules going across the membrane, from high to low. Passive also has facilitated diffusion, which consists of small polar molecules being transported via transport proteins. Osmosis is the diffusion of water from a high concentration of solute to a low concentration. In active transportation, molecules are moved against their gradient (low to high), require extra energy, and assistance from a protein pump. Two types of active transport, one is primary and the other is secondary. Primary moves molecules from low to high using ATP. In secondary, which uses preexisting gradient to drive transport of solute. One molecule is moving down the gradient while pulling the secondone along. The last method of transportation is bulk. This is the transportation of larger molecules such as proteins and carbohydrates. Exocytosis is one form of bulk transport and it is moving molecules out ofthe cell via vacuoles. The other type is Endocytosis and this is when the cell brings in large molecules. This is split up into three different forms, phagocytosis, pinocytosis, and receptor-mediated endocytosis. Phagocytosis is when the plasma membrane extends outward to engulf a molecule. Pinocytosis is when the plasma membrane folds inward to capture molecules. Receptor- mediated endocytosis is a specialized form of pinocytosis. It is specific because of the certain molecule receptors on the membrane, so it only takes the molecules needed.TonicityTonicity is the ability of a solution to cause a solution to gain or lose water. There are three types of tonicity: hypertonic, hypotonic, and isotonic. Hypertonic is when there is a higher solute, hypotonic is when there’s less solute present, and isotonic is when there is equal amount of solute in and out of the cell. When an animal cell is placed in a hypertonic solution, all of the water rushes out of the cell, leavingthe cell dehydrated and shrunk. When in a hypotonic solution, water rushes into the animal cell, causing it to swell and burst (known as lysed). Tonicity in plants is a little different. When a plant cell is in a hypertonic solute, all of the water rushes out of the cell leaving the cell wall to detach from the membrane (known as plasmolyzed). When a plant cell in a hypotonic solution, the cell will just hold all of the water rushing into it, this is known as
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