The Cell Membrane FOS 3 Infectious Disease Unit
Composition of Cell Membrane Cell Membranes are NOT all identical, but have FOUR common parts: Lipid Bilayer Transmembrane Protein Network of supporting fibers Glycoproteins On outside of cell Cell Surface has a carbohydrate coat to prevent sticking.
If you want more information of this go to:http://www1.umn.edu/ships/9- 2/membrane.htmHistory of the Fluid Mosaic Model
Controls the fluidity of the Cell MembraneTemperatureLength of tails and kinks in tailsCholesterol
How do things get through if there is a barrier? Simple diffusion. Through “kinks” in the fatty acid tails Closely aligned tails have C-C (single bonds) C=C (double/triple bonds) cause “kinks”
Transmembrane Proteins extend across lipid bilayer These proteins can have both a polar and a nonpolar region. Enables them to be embedded in the nonpolar (hydrophobic) area of the membrane Polar regions are anchored in the water Provide CHANNELS into the cell but only for selected items.
Proteins act as Cell Identification MarkersLipids and proteins within the membrane may have a carbohydrate chain attachedThese glycolipids and glycoproteins often function as cell ID markers, allowing cells to identify other cellsThis is particularly important in the immune system where cells patrolling the body’s tissues identify and destroy foreign invaders such as bacteria or viruses.
Cell Surface ReceptorsIt’s shape fits signal molecules, such as hormones.Receptors enable cells to detect hormones and a variety of other chemicals in their environmentThe binding of a molecule and a receptor initiates a chemical change within the cell.
Channel Proteins In some cases the channel proteins simply act as a passive pore. Molecules will randomly move through the opening in a process called diffusion. This requires no energy, molecules move from an area of high concentration to an area of low concentration.
Carrier ProteinsThey do not extend through the membraneThey bond and drag molecules through the lipid bilayer and release them on the opposite side.
Proteins used to attach CytoskeletonReceptor proteins help to attach the cytoskeleton inside the cell.
Cholesterol in Cell Membrane The phospholipid bilayer also contains cholesterol molecules. This gives the layer greater strength, more flexibility, less fluid and less permeable to ions and monosaccharides.
Major Histocompatibility ComplexUnique to every individual Except identical twinsConsists of proteins that attach to exterior cells and antigensAllows T-Cells in the immune system to recognize and attack foreign cellsGlycolipids also differentiate between tissues of same individual A, B, AB and O blood group markers.