细胞工作原理 大学生物 The Working cell.ppt

Membrane Structure and Function Membranes are fluid mosaics of lipids and proteins with many functions. In animal cell membranes, the steroid cholesterol helps stabilize the membrane at warm temperatures but also helps keep the membrane fluid at lower temperatures. Figure 5.1 illustrates six major functions performed by plasma membrane proteins. Passive transport is diffusion across a membrane with no energy investment. The Working cell 5. Facilitated diffusion is a type of passive transport because it dose not require energy. 6. Substance that use facilitated diffusion for crossing cell membrane include a number of sugar, amino acids, ions and even water. 7. The very rapid diffusion of water into and out of certain cells, such as plant cells, kidney cells, and RBC, is made possible by a protein channel called an aquaporin. 8. The walled cells of plant, bacteria, and fungi also plasmolyze in hypertonic environments. Thus, meats and other foods can be preserved with concentrated salt solutions. * 10. Cells expend energy against its concentration gradient in the active transport of a solute. 11. Figure 5.8 shows a simple model of an active transport system that pumps a solute out of the cell against its concentration gradient. 12. Exocytosis and endocytosis transport large molecules across membranes. 13. ATP powers nearly all forms of cellular work. 14. There are three main types of cellular work (as Figure 5.12B shows): (1) Chemical work (2) Mechanical work (3) Transport work * * * 15. The phosphorylation usually does so by transferring a phosphate group from ATP to some other molecule. 16. Cellular work can be sustained because ATP is a renewable resource that cells regenerate. 17. An enzyme speeds up a reaction by lowering the activation energy needed for a reaction to begin. 18. Almost all enzymes are proteins, although some RNA molecules can also function as e