Cell Organelles Essay

4101 WordsOct 21, 201317 Pages
Section 3.3 Notes – Cell Membrane Cell Membranes Are Composed of 2 Phospholipid Bilayers. Cell membrane, or plasma membrane, forms boundary btwn. cell & outside environ. & controls passage of materials into & out of cell. Cell membrane consists of double layer of phospholipids interspersed w/ variety of other molecs. Phospholipid is molec. composed of 3 basic parts: charged phosphate group, glycerol, & 2 fatty acid chains. Together, glycerol & phosphate groups form “head” of phospholipid; fatty acids form “tail.” B/c head bears change, it’s polar. H2O molecs. are also polar. Therefore, polar head of phospholipid forms hydrogen bonds w/ H2O molecs. In contrast, fatty acid tails are nonpolar & can’t form hydrogen bonds w/ H2O. As result, nonpolar tails are attracted to each other & repelled by H2O. Polar heads are like bread. They form the outer surfaces of membrane, where they interact w/ H2Oy environ. outside & inside cell. Nonpolar tails are like filling. They’re sandwiched btwn. layers of polar heads, where they’re protected from H2Oy environ. Other molecs. embedded w/in phospholipid layers give membrane properties & characteristics it wouldn’t have otherwise. These molecs. serve diff. functions. Here are few exs.: • Cholesterol molecules strengthen cell membrane. • Some proteins extend thru. 1 or both phospholipid layers & help materials cross membrane. Other proteins are key components of cytoskeleton. Diff. cell types have diff. membrane proteins. • Carbs. attached to membrane proteins act as id. tags, letting cells distinguish 1 type of cell from other. Fluid Mosaic Model Scientists have developed fluid mosaic model, which describes arrangement of molecs. that make up cell membrane. This model of cell membrane structure takes its name from 2 characteristics. 1st, cell membrane is flexible, not rigid. Phospholipids in each layer can move from side

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