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Cell Membranes and Transport. B9 - Analyze the structure and function of the cell membrane. Cell Walls. NB** Cell walls are different from cell membranes Stiff, non-living Made of complex carbohydrates Cellulose for plants Chitin for fungi Chitin-like frame for bacteria
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Cell Membranes and Transport B9 - Analyze the structure and function of the cell membrane
Cell Walls • NB** Cell walls are different from cell membranes • Stiff, non-living • Made of complex carbohydrates • Cellulose for plants • Chitin for fungi • Chitin-like frame for bacteria • Used for support and protection • Very porous; entry only controlled by size
Cell Membranes “gate keepers” • 1. Isolate form outside • 2. Control entry and exit • 3. Communicate with others • 4. Bare identification (I’m one of you!)
Which of these statements are true comparing cell walls with membranes?
Fluid Mosaic Model • A phospholipid bilayer with proteins scattered through it • “fluid” because the proteins seem to “float” around the bilayer • Hydrophilic heads on the outside • Hydrophobic tails on the inside
Hydrophobic layer is a barrier to H2O soluble molecules (but makes it less fluid)
Cholesterol in the bilayer is even less permeable to H2O soluble molecules (but makes it less fluid)
“Protein Mosaic” • Membrane proteins will interact with the hydrophobic and hydrophilic layers of the bilayer • Some proteins will protrude into the cytoplasm, some into the extracellular space, others into both
Glycoproteins • Membrane proteins that have a carbohydrate chain attached • Often seen in proteins that protrude outside the cell
Glycolipids • Membrane lipids that have a carbohydrate chain attached • Both glycoproteins and glycolipids OFTEN function in cell-to-cell communication and/or recognition
What does the “fluid” in “fluid mosaic model” refer to? • A. The structure of the cell membrane • B. The structure of the cell wall • C. The fact that the membrane is made up mostly of water • D. The fact that the membrane is always changing, so it seems to be “fluid” • E. The fact that the membrane is made up of lipids, and they tend to “flow”
What does “mosaic” mean? • A. a picture • B. a lipid • C. a bunch of different things clumped together on a background • D. a type of protein that lets things into the cell • E. No idea!
Which of the following is true regarding this diagram? • A. 1a and 1b are fatty acids • B. 3 is a phosphate group • C. 5 is the hydrophobic end of the molecule • D. 6 is the hydrophobic end of the molecule • E. this is a type of lipid
Which one is a: • 1. Phospholipid • 2. Glycoprotein • 3. Cholesterol
3 major membrane Protein Categories: • 1. Transport proteins • Regulated, fast method for specific molecules to enter and exit • Channel proteins • Carrier proteins
2. Receptor Proteins • When activated, set off enzymatic sequences inside the cell
3. Recognition Proteins • “identification tags”
Membrane Transport - RATE • Depends on: • Gradient (concentration, electrical or pressure) • Size of molecule • Lipid solubility • # of transporters
Diffusion • The random net movement of molecules from an area of high concentration to an area of low concentration. • (this is following the “concentration gradient”)
Osmosis • The diffusion of WATER across a selectively permeable membrane • (this is also following the “concentration gradient” and does not require energy)
Osmotic Effects • Isotonic solution • Same solute concentration • Cell is happy (no net loss or gain of water)
HYPERtonic solutions • [Solute] is greater outside the cell than inside the cell • Cell is not happy • It will crenate (shrink)
HYPOtonic solutions • Solute concentation is less outside the cell than inside • Cell is not happy • Cell will lyse
Active transport • Often against the concentration gradient • Therefore, REQUIRES ENERGY • (ATP --> ADP + P) • Uses transporter proteins
2. Pinocytosis • Liquid and • smaller particles only
Receptor-mediated Endocytosis • Uses receptors to bind first to the desired molecules, then gathers them together before enclosing them in a membrane