Chapter 7 6q692f

Malak Younis Chapter 7 Membrane Structure & Function Objectives Membrane Structure 1. Explain why phospholipids are amphipathic molecules. Because both hydrophobic region tail and hydrophilic head. Head composed phosphate group attached to one carbon of glycerol is hydrophilic.

2.

Explain what freeze-fracture techniques reveal about the arrangement of proteins in membranes. A cell is frozen and fractured with a knife. The fracture plane often follows the hydrophobic interior of the membrane, splitting the phosphoslipid bilayers into two separated layers. The membrane proteins go wholly with one of the layers. 3. Describe the fluidity of the components of a cell membrane and explain how membrane fluidity is influenced by temperature and membrane composition. Phospholipids can move side to side or laterally making the membrane fluid. 4. Explain how cholesterol resists changes in membrane fluidity with temperature change. The steroid cholesterol has a different effect on the membrane fluidity at different temperatures. Traffic Across Membranes 5. Distinguish between peripheral and integral membrane proteins. Integral proteins penetrate the hydrophobic core of lipid bilayer. Peripheral proteins are appendages loosely bound to the surface of the membrane. 6. List six major functions of membrane proteins. Transport, enzymatic activity, signal transduction, cell- cell recognition, intercellular , and attachment to the cytoskeleton and extracellular matrix. 7. Explain the role of membrane carbohydrates in cell-cell recognition. Membrane carbohydrates interact with surface molecules of other cell, facilitating cell-cell recognition. 8. Explain how hydrophobic molecules cross cell membranes. Hydrophobic molecules are lipid soluble and can through the membrane rapidly. 9. Distinguish between channel proteins and carrier proteins. Both are integral membrane proteins involved in moving a molecule or ion across a membrane. Both have only one or a couple specific molecules. The different is how they accomplish this task. Carrier proteins transport molecules by changing shape. Channel proteins usually transport or very small molecules down a concentration gradient, and are more like a hollow tube that can or shut. 10. Define diffusion. Explain why diffusion is a spontaneous process. ive transport is different of substance across a membrane with no energy investment. 11. Explain why a concentration gradient of a substance across a membrane represents potential energy. Isotonic the concentration of solutes is the same as it is inside the cell. Hypertonic the concentration of solutes is greater than it is inside the cell. Hypotonic the concentration of solutes is less than it is inside the cell. 12. Distinguish among hypertonic, hypotonic, and isotonic solutions. Isotonic the concentration of solutes is greater than it is inside the cell. Hypotonic the concentration of solutes is less than it is inside the cell.

13. Define osmosis and predict the direction of water movement based on differences in solute concentrations. Osmosis is the movement of water across a semipermeable membrane. 14. Describe how living cells with and without cell walls regulate water balance. Tonicity is the ability of solution to cause a cell to gain or lose water has a great impact on cells without walls. 15. Explain how transport proteins facilitate diffusion. In facilitated diffusion transport proteins speed the movement of molecules across the plasma membrane. 16. Distinguish among osmosis, facilitated diffusion, and active transport. Active transport uses energy to move solutes against their concentration gradient requires energy, usually in the form of ATP. Active transport is the sodium-potassium pump. Osmois is proteins speed the movement of water across a semipermeable membrane. In facilitated diffusion transport proteins speed the movement of molecules across the plasma membrane. 17. Describe the two forces that combine to produce an electrochemical gradient. Membrane potential is the voltage difference across a membrane. An electrochemical gradient is caused by the concentration electrical gradient of ions across a membrane. 18. Explain how an electrogenic pump creates voltage across a membrane. A transport protein generate with tage across a membrane. 19. Describe the process of cotransport. Cotransport occur when active transport of a specific solute indirectly drive the active transport of another solute, involves transport by membrane protein driven by concentration gradient. 20. Explain how large molecules are transported across a cell membrane. Bulk transport across the plasma membrane occurs by exocytosis and endocytosis. 21. Distinguish between pinocytosis and receptor-mediated endocytosis. In endocytosis the cell takes in macromolecules by forming new vesicle from the plasma membrane. In pinocytosis, the cell “gulp” droplets of extracellular fluid into tiny vesicles.