1 / 15

Cell Membranes

Cell Membranes. I . All cells are enclosed in a Plasma (Cell) Membrane. Separates the cell from its surroundings Regulates the contents of the cell Allows the passage of some materials but not others . II. Membrane Structure. A. Phospholipid Bilayer Composed of phospholipids

nieve
Download Presentation

Cell Membranes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Cell Membranes

  2. I. All cells are enclosed in a Plasma (Cell) Membrane • Separates the cell from its surroundings • Regulates the contents of the cell • Allows the passage of some materials but not others II. Membrane Structure A.Phospholipid Bilayer Composed of phospholipids - hydrophilic “head” - hydrophobic “tails” “head” “tails”

  3. B. “Fluid-Mosaic” Model 1. “Fluid” because of flexible nature 2. “Mosaic” of proteins located within the lipid bilayer Transport Proteins Receptor Proteins Recognition Proteins bind substances that trigger changes in cell activities help molecules through bilayer cell “fingerprints” that identify cells

  4. Osmosis and Diffusion

  5. A solution is a liquid consisting of two or more substances evenly mixed • The dissolving agent is called the solvent (eg. water) • The dissolved substance is called the solute (eg. salt) Salt crystal Ion in solution Figure 2.16

  6. III. How Substances Cross Cell membranes • Simple Diffusion= the net movement of like molecules down theirconcentration gradient (from HI to LO) HI HI solute LO solvent (One type of molecule) HI “blue”, LO “red” HI “red” LO “blue” solute solvent (Two types of molecules)

  7. Molecules of dye Membrane Equilibrium (a) Passive transport of one type of molecule Equilibrium (b) Passive transport of two types of molecules Figure 5.11 • Molecules tend to spread into the available space • Diffusion is passive transport; no energy is needed

  8. - Molecules reach a Dynamic Equilibrium when their net distribution on both sides is approximately the same - Molecules still move in and out of the cell, but the overall distribution will no longer change One type of molecule Two types of molecules

  9. B. Membrane Channels and Facilitated diffusion The movement of solute down its concentration gradient aided by transport proteins 1. Membranes are Selectively Permeable Allowing some substances to move across more easily than others or preventing their movement altogether 2. Ions and large, polar molecules cannot pass directly through the lipid bilayer and so must cross through channel proteins

  10. C. Osmosis The movement of water across a selectively permeable membrane 1. Depends on solute concentrations on either side of membrane 2. Movement is toward region where solute is more concentrated solvent + solute solvent Net movement of water

  11. 3. How does osmosis affect cells? ? What happens to a cell when the surrounding environment is… a.Isotonic = same solute concentration b.Hypotonic = lower solute concentration c. Hypertonic = higher solute concentration (Cell) 2M Sucrose c. a. b. 2M Sucrose 10M Sucrose Distilled Water

  12. Plant cells HYPOTONIC HYPERTONIC ISOTONIC Animal cells

  13. D. Active Transport = transport proteins move solute against concentration gradient - requires input of Energy (ATP) - net movement to side where solute is more concentrated Up the concentration gradient (LO to HI) NEEDS ENERGY !

  14. E. Exchange of Large Molecules • 1. Endocytosis • = substances taken into • the cell • Plasma membrane pinches • inward, forming a membrane- • enclosed vesicle 2. Exocytosis = substances released out of the cell - membrane-enclosed vesicles move to the cell surface and fuse with plasma membrane - contents of vesicle released

  15. Study Objectives 1. Describe the functions of the plasma (cell) membrane. 2. Describe the structure of a phospholipid. 3. Define hydrophobic and hydrophilic. 4. Describe the structure of the “lipid bilayer”. 5. Explain why the membrane structure is described as a “fluid-mosaic”. 6. Describe the 3 types of membrane proteins and their functions. 7. Define solvent and solute. 8. Define concentration gradient. 9. Define dynamic equilibrium. 10. Compare and contrast simple diffusion, osmosis, and facilitated diffusion. 11. Explain what happens to a cell in a hypotonic, hypertonic, and an isotonic solution. 12. Define selectively permeable (semipermeable) 13. Contrast passive and active transport. 14. Explain endocytosis and exocytosis. For what type of molecules are these processes used?

More Related