Cell Membrane.pdf - Republic of the Philippines Department...

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Republic of the PhilippinesDepartment of EducationRegion VIII – Eastern VisayasSchools Division of Calbayog CityCALBAYOG CITY NATIONAL HIGH SCHOOLSCHOOL ID: 313801P2 Brgy. Hamorawon, Calbayog City, Western Samar 6710 . Tel Nos. PLDT-(055) 209-1535Email: calbayogcit[email protected], [email protected]Module 7: The Cell MembraneAt the end of this module, I can:1. Explain the fluid mosaic model of the cell membrane.2. Relate the structure and composition of the cell membrane to its function.3. Explain transport mechanisms in cells: those requiring no energy (passive transport) and thoserequiring energy (active transport and bulk transport)You have learned that different organelles perform different functions. These functions areimportant in maintaining the processes that keep cells alive. The focus of this module will be on the cellmembrane and its important roles. Keep in mind that the primary responsibility of the cell membrane isto facilitate the entry and exit of different substances in the cell.The Fluid Mosaic ModelThe most acceptable cell membrane model today is the fluid mosaic model. The fluid mosaicmodel was first proposed by Seymour Jonathan Singer and Garth L. Nicolson in 1972 to describe thestructure of cell membranes.The model is “fluid” because the various functional macromolecules embedded in thephospholipid matrix of the cell membrane can move about the surface of the cell. Also, the membrane,according to this model, is made up of various parts (i.e., proteins, carbohydrates, and cholesterol) thatpave the surface of the matrix just like individual tiles, hence the “mosaic” appearance.How did scientists prove that the lipid bilayer is really fluid? In an experiment, a cell surface wasimmersed in a dye, resulting in the coloration of the lipids. Then, the laser bleached an area of the cellsurface. This removed the color of the lipids in that area. After a few seconds, the bleached lipidmolecules moved out of the laser-treated area, while the colored lipid molecules moved in.This fluid mosaic model allows the membrane to perform multiple functions... For example,certain embedded proteins in the membrane may act as channels allowing particular molecules to passthrough the membrane. Some may serve as labels, allowing recognition of the cell. Still, other parts ofthe membrane may act as sensors that detect various features of the ambient environment (i.e.,surrounding all sides) of the cell.Fig. 3.2. The Fluid Mosaic ModelAdapted from.brooklyn.cuny.edu/biology/bio4fv/page/pm_mos.htm
Aphospholipidis amphipathic, which means it has hydrophilic and hydrophobic ends. Thehydrophilic head, made up of a phosphate group, has affinity with water, whereas the hydrophobic tail,made up of fatty acids, does not. On the tail of the phospholipid is a kink. The kink is due to a doublebond in the unsaturated fatty acid. The kink prevents the tight packing of the phospholipid, hence itsfluid movement.

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