The Cell Membrane

1. The Cell Membrane

2. Function • Regulates the movement of materials from one environment to the other. • Transports raw materials into the cell and waste out of the cell. • Prevents the entry of unwanted matter and the escape of needed materials. • Maintain a steady environment: Homeostasis

3. Structure: • Composed of a phospholipid bilayer with a collage of many different proteins, lipids and carbohydrates. • A Phospholipid is composed of 1 glycerol molecule, 2 fatty acids and 1 phosphate group. This structure causes hydrophilic and hydrophobic regions.

5. The Fluid-Mosaic Membrane Model • Membranes are not static; they have a fluid consistency. • Most membrane lipids and proteins can drift about laterally in the plane of the membrane. • Cholesterol enhances membrane fluidity, allows animal membranes to function in a wide range of temperatures and also makes the membrane less permeable to biological molecules.

6. Membrane Proteins: Two Types: • Integral: Proteins that insert into the membrane (transmembrane proteins) • Peripheral: Proteins attached to the surface of the cell membrane. Function: • Transportation • Enzymes • Receptor sites • Cell adhesion • Attachment to the cytoskeleton

7. Carbohydrates: • Usually branched molecules of 15 or less sugar units. • Some are bonded to lipids: Glycolipids. • Most are bonded to proteins: Glycoproteins. • Function: Cell-cell recognition.

9. Construction of a Cell Membrane Copy the link below to create your own cell membrane. http://www.wisc-online.com/objects/index_tj.asp?objID=AP1101

10. Through the Cell Membrane • Diffusion • Osmosis • Facilitated Diffusion • Active Transport • Bulk Transport

11. 1. Diffusion: • Passive movement of molecules from a region of high concentration to a region of low concentration. • (Concentration gradient is the difference in concentration between the two regions) • Small, uncharged molecules like O2, CO2 and H2O can move easily through the membrane. • Works well over short distances. Once molecules enter the cell the rate of diffusion slows. • Limits cell size.

12. Passive Transport

13. 2. Osmosis • Diffusion of the solvent across a semi-permeable membrane separating two solutions. (Diffusion of water) • Water molecules move from a region of high concentration to a region of low concentration. • Direction depends on the relative concentration of water molecules on either side of the cell membrane. • Isotonic: Water inside the cell equals the water outside the cell and equal amounts of water move in and out of the cell. • Hypotonic: Water outside the cell is greater than that inside the cell, water moves into the cell, may cause cell to burst (lysis) • Hypertonic: Water inside the cell is greater than outside. Water moves out of the cell, may cause the cell to shrink (plasmolysis)

15. Osmosis: Hypotonic

16. 3. Facilitated Diffusion • Assists with the movement of large molecules like glucose. • Passive movement of a substance into or out of the cell by means of carrier proteins or channel proteins. • Moves molecules from high to low regions of concentration. • Carrier proteins: Transports non-charged molecules with a specific shape. • Channel proteins: Tunnel shape that transports small charged molecules.

17. 4. Active Transport • The process of moving substances against their concentration gradients. Requires energy. • Examples: • Kidney cells pump glucose and amino acids out of the urine and back into the blood. • Intestinal cells pump in nutrients from the gut. • Root cells pump in nutrients from the soil. • Gill cells in fish pump out sodium ions. • Active Transport Pump: • Sodium-potassium pump • 3 sodium ions inside the cell and 2 potassium ions outside the cell bind to the pump. • This allows the release of energy from ATP and causes the protein complex to change shape. • The change in shape allow the Na + and K+ ions to move across and be released.

18. Active Transport Pump

19. 5. Bulk Transport 1. Endocytosis: The cell membrane folds inward, traps and encloses a small amount of matter from the extracellular fluid. 3 types:

20. Endocytosis • Pinocytosis: The intake of a small droplet of extracellular fluid. This occurs in nearly all cell types. • Phagocytosis: The intake of a large droplet of extracellular fluid. This occurs in specialized cells. • Receptor-assisted endocytosis: The intake of specific molecules that attach to special proteins in the cell membrane. These proteins are uniquely shaped to fit the shape of a specific molecule.

21. Bulk Transport 2. Exocytosis: The reverse of endocytosis: A vesicle from inside the cell moves to the cell membrane. The vesicle fuses to the membrane and the contents are secreted