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Transcript
CELL MEMBRANE Structure & Function This lesson meets the following DoE Specific Curriculum Outcomes for Biology 11: 314-1, 314-2, 314-3, 314-8 CELL MEMBRANE • Each cell is a separate unit of life, therefore, it has a boundary – the plasma membrane (a.k.a., cell membrane). • The cell membrane separates the inner contents of a cell from its external environment - it maintains a constant internal environment despite changes to its outside world. • It forms spontaneously - no energy is required of the cell to maintain the integrity of the plasma membrane. CELL MEMBRANE • Cells live in a fluid environment (i.e. blood, water, extra-cellular fluid) and exchange materials with this fluid. • The plasma membrane is the cell’s “gate keeper” - it allows the passage of some materials in and out of the cell but not others. • The plasma membrane brings in the ‘good’ things and keeps them in, and it exports the ‘bad’ things and keeps them out. CELL MEMBRANE • Small particles (e.g., O2, CO2) generally pass through the plasma membrane easily. • Lipids (and particles that are soluble in lipids) pass through with least difficulty. • The plasma membrane tends not to be permeable to polar molecules unless they are small. CELL MEMBRANE • Membrane consists of two layers of phospholipids (phospholipid bilayer). • Phospholipids consist of a polar phosphate containing head and two non-polar lipid tails. A phospholipid bilayer One phospholipid molecule CELL MEMBRANE • Phospholipid heads are hydrophylic (water loving) they orient toward water both inside and outside the cell. • Phospholipid tails are hydrophobic (water hating) they orient toward each other CELL MEMBRANE • Fluid Mosiac Model: components of membrane are constantly moving (like a fluid). • The phospholipids can move and slide past each other. • In some cells, cholesterol molecules bind to the phospholipids to help restrict their movement. CELL MEMBRANE • The plasma membrane is embedded with proteins. • They have polar and non-polar ends to determine their position in the bilayer. • They can move sideways throughout the plasma membrane. CELL MEMBRANE • The roles of these proteins include: – regulation of the movement of particles across membrane – involvement in chemical reactions – act as ‘marker’ on the cell.