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Plasma Membrane

Plasma Membrane. Plasma Membrane. Separates intracellular (within the cell) fluids from extracellular (outside the cell) fluids Made up of lipids, proteins and carbs (on outer surface) Plays a dynamic role in cellular activity & homeostasis

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Plasma Membrane

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  1. Plasma Membrane

  2. Plasma Membrane • Separates intracellular (within the cell) fluids from extracellular (outside the cell) fluids • Made up of lipids, proteins and carbs (on outer surface) • Plays a dynamic role in cellular activity & homeostasis • Controls and regulates what enters and leaves the cell

  3. Lipids in the Membrane • Glycolipids are found only in the outer membrane surface • 20% of all membrane lipid is cholesterol • Maintain mobility of phospholipids in membrane • Lipid Rafts: • Make up 20% of the outer membrane surface • Composed of sphingolipids and cholesterol • Are concentrating platforms for cell-signaling molecules

  4. Glycocalyx • a fuzzy, sticky carb.-rich area (“sugar-coating”) • Made up of glycoprotein on the surface of the cell • Acts as highly specific biological markers by which cells recognize one another • Examples: • sperm recognize ovum by its glycocalyx • immune cells recognize bacteria by their glycocalyx.

  5. Cell Membrane Proteins • Proteins play a major role in membrane functions • 2 main types: • Peripheral-on outside or inside of membrane • Integral- are imbedded into membrane • Some go through entire membrane, others do not

  6. Functions of Membrane Proteins • Transport-spans the membrane and is selective for a particular solute • Some use ATP to actively pump across membrane • Enzymatic activity- some membrane proteins may be enzymes • Receptors for signal transduction-have a specific binding site on outside of cell, once stimulated may initiate a chain reaction in the cell. Figure 3.4.1

  7. Functions of Membrane Proteins • Intercellular adhesion-adjacent cells can hook together • Cell-cell recognition-glycoproteins (proteins bonded to short sugar chains) act as an ID tag to other cells • Attachment to cytoskeleton and extracellular matrix- anchor cell, help maintain cell shape and/or maintain location. • Some play role in cell movement or binding to adjacent cells Figure 3.4.2

  8. Microvilli • “little shaggy hairs” • Minute, fingerlike extensions that project from an exposed cell surface • Increase plasma membrane surface area greatly • Found typically on surface of absorption cells

  9. Membrane Junctions • Most cells are bound to other cells • 3 factors typically act to bind cells together: • Glycproteins act as an adhesive • Wavy contours of membranes on adjacent cells fit together in a zipper fashion • Special membrane junctions are formed- 3 types:

  10. 1. Tight Junction • impermeable junction that encircles the cell Examples: between epithelial cells in digestive tract keep unwanted material from seeping into blood stream Figure 3.5a

  11. 2. Desmosome • anchoring junction scattered along the sides of some cells • Keeps cells from being pulled apart during mechanical stress Examples: Skin and heart muscle Figure 3.5b

  12. 3. Gap Junction • a nexus that allows chemical substances to pass between cells Example: electrically excitable tissues like heart and smooth muscle Figure 3.5c

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