Membrane Structure and Function

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3. Membrane Structure and Function

4. A Cellular Membrane • Is a mosaic of • proteins and carbohydrates • floating in a fluid bi-layer • of phospholipids.

5. Cellular Membrane • Proteins are • embedded in the bilayer • or attached to the surface.

6. Cellular Membrane • Carbohydrates are • linked to the proteins and • linked to the lipids.

7. Selective Permeability • A property of biological membranes • Allows some substances to cross the cell membrane more easily than others.

8. Selective Permeability • small nutrient • waste molecules • respiratory gases • inorganic ions. • The plasma membrane regulates the passage of these substances.

9. Passive Transport • Passive transport is diffusion across a membrane

10. Diffusion • Diffusion is the spontaneous movement of a substance down its concentration gradient. • From a more concentrated to a less concentrated area.

11. Osmosis • Osmosis is the passive transport of water. • Water flows across a membrane from the side with a lesser concentration of solute (hypotonic) to the side with the greater solute concentration (hypertonic).

12. Cell Survival Depends on Balancing Water Uptake and Loss • Cells lacking walls (as in animals and some protists) are either isotonic with their environments or else have adaptations for osmoregulation. • Plants, prokaryotes, fungi, and some protists have an elastic wall around their cells, which keeps the cells from bursting in a hypotonic environment. Under such conditions, these cells are turgid.

13. Specific Proteins Facilitate the Passive Transport of Selected Solutes • In facilitated diffusion, transport proteins hasten and help the movement of certain substances across a membrane. • Diffusion, osmosis, and facilitated diffusion are all passive transport processes that do not require the input of energy from the cell.

14. Active Transport Is The Pumping of Solutes Against Their Gradients • Energy, usually in the form of ATP, is harnessed by specific membrane proteins that perform the active transport. • Some ion pumps generate voltage across membranes. • In co-transport, a membrane protein couples the transport of one solute to another.

15. Exocytosis and Endocytosis Transport Large Molecules • Exocytosis- intracellular vesicles migrate to the plasma membrane, fuse with it, and release their contents. • Endocytosis- large molecules within vesicles pinch inward from the plasma membrane.

16. Endocytosis-Transport of Large Molecules into the cell. • Three types of endocytosis are: • Phagocytosis- the ingestion of large particles or whole cells; • Pinocytosis- the intake of tiny droplets of extracellular fluid with all its contained solutes; and • receptor–mediated endocytosis- the ingestion of specific substances that bind to receptor proteins on the membrane.

17. Specialized membrane proteins • Specialized membrane proteins transmit extracellular signals to the inside of the cell. Biology

18. Websites www.bmb.psu.edu/courses/bisci004a/cells/cellstruc.htm