1. CHAPTER 5 The Working Cell

2. Energy The capacity to do work Comes in two forms: Kinetic energy – it does work e.g. heat or light produced by molecular movement/breaking of chemical bonds - gravity or friction Sect 5.1

3. Potential energy – it is stored energy e.g. chemical energy stored in molecular bonds (most important type of energy for living organisms)

4. Governing Laws of Energy Conversion Thermodynamics – the study of energy conversions in matter sect 5.2 System-matter under study Surroundings-everything outside the system Open system-exchanges both energy & matter w/surroundings (living organism)

5. 2 Laws of Thermodynamics First Law of Thermodynamics – (Law of Energy Conservation) energy can be transferred and transformed but not created or destroyed 1) solar (light) energy is stored in glucose’s chemical bonds during photosynthesis 2) chemical energy in glucose is converted into a useable form for cells in ATP

6. Second Law of Thermodynamics - energy conversions reduce the state of order, or increases entropy (amount of disorder in a system) in the universe 1) energy conversions are not 100% efficient, energy lost to the universe (usually heat or light) 2) energy is lost in every cellular chemical reaction

7. Life’s Chemical Reactions Endergonic reactions - require energy input (energy stored in covalent bonds of product molecules); e.g. photosynthesis producing glucose Sect 5.3

8. Exergonic reactions - releases energy e.g. burning wood (1 step means releasing all at once), cellular respiration (many steps - heat and chemical energy of ATP) Chemical energy converts glucose’s energy to ATP

9. Cellular metabolism - the sum of endergonic and exergonic reactions in an organism

10. ATP Shuttle ATP (Adenosine triphosphate) is the power unit that shuttles energy used in cellular work it uses energy coupling - using energy from exergonic reactions to drive endergonic reactions Sect 5.4

11. ATP uses unstable bonds between its phosphate groups the breakdown of glucose: 3 Things Happen: 1) a phosphate is removed 2) ATP becomes ADP 3) energy is released (p. 75)

12. Phosphorylation - the energy from ATP is actually released in the 3rd phosphate and transferred to a molecule most cellular work depends on ATP energizing other molecules by phosphorylating them Fig. 5.4B p. 75 ATP is a renewable source of energy (recycle 10 million ATP each second)

13. How Enzymes Work Speeding up Chemical Reactions energy of activation (E A ) is the amount of energy needed to start a chemical reaction (breaking the bond between the 2nd and 3rd phosphate) Sect 5.5

14. in many essential metabolic processes in our body E A is too high for processes to occur quickly enough otherwise things would denature E A acts as a barrier in sustaining life Enzyme - protein molecule that serves as a biological catalyst

15. enzymes lower this barrier by lowering the E A and speeding up the rate of reactions w/out being changed itself

16. Enzyme Specificity Very selective on the reactions they catalyze because of their 3-D shape Substrate(s) is the reactant in a chemical reaction the enzyme acts upon Sect 5.6

17. Enzyme and substrate bind at the enzyme’s active site (groove or pocket); this changes the substrate in the product(s) Because of an enzyme’s specificity for a given substrate(s), many different enzymes are needed to catalyze all of a cell’s reactions p.77

18. Cellular Environment Body’s pH (6-8) Temperature (35-40 o C) Salt concentration (around 4%) Many enzymes need non-protein helpers: cofactors – inorganic molecules (Zn, Fe, Cu) coenzymes – organic molecules made from vitamins or vitamins themselves Sect 5.7

19. Enzyme Inhibitors Interfere with an enzyme’s activity Competitive Inhibitor(p. 78) – substrate that resembles the enzyme’s normal substrate and competes for the active site Sect 5.8-5.9

20. Noncompetitive Inhibitor (p.78) -substrate that does not compete for the normal substrate’s active site - binds at another active site - alters the normal substrate’s active site (no binding occurs for the normal substrate)

21. Most inhibition is reversible because of weak H-bonds and is used by cells to regulate metabolism Feedback Inhibition – substrate exceeds demand and inhibits its enzyme until substrate levels become lower Many pesticides and antibiotics irreversibly inhibit enzymes of the target organisms (covalent bonds form instead of H-bonds)

22. Membrane Form & Functions Selective Permeability Items needed by the cell enter and waste products leave through the PM All other substances are blocked from entry Sect 5.10- 5.13

23. Membrane Structure Phospholipid Bilayer Composed of 2 layers w/each layer made of molecules that have: - polar,hydrophilic head w/a phosphate group - 2 nonpolar,hydrophobic hydrocarbon tails p. 79 Fig. A (look at 3 lines)

24. In water, these molecules will spontaneously form the 2-layer framework called the phospholipid bilayer water Hydrophilic heads Hydrophobic tails water

25. Fluid Mosaic Mosaic refers to the membrane surface w/many different embedded proteins Fluid refers to lateral drifting of individual proteins and phospholipids w/in the membrane

26. Also embedded in the surface are glycoproteins and glycolipids (sugars attached to proteins or lipids) that recognize self from nonself Ex: white blood cells, embryo

27. Other membrane proteins function as: 1)Enzymes 2)Receptors of chemical messages from other cells which can relay a signal to inside the cell – signal transduction 3)Transport molecules through cell membrane

28. Traffic Across Membranes Passive Transport -Osmosis -Osmoregulation -Facilitated Diffusion Active Transport -ATP -Exocytosis -Endocytosis

29. Passive Transport - based on diffusion of molecules across a cell membrane no energy used movement of high [ ] of molecules down its concentration gradient toward low [ ] to achieve equilibrium O 2 in lungs vs blood/CO 2 in blood vs lungs Sect 5.15

31. Osmosis – special case of diffusion of water across a cell membrane Hypertonic – soln has a relatively higher amount of solute molecules than water molecules Hypotonic – soln has a relatively higher amount of water molecules than solute molecules Isotonic – the [ ] of water molecules is the same on each side of the membrane Sect 5.16

32. water will move across a membrane from hypotonic to hypertonic to reach an equilibrium Tonicity – tendency of a cell in a given solution to lose or gain water Osmoregulation – a process of cells to control water balance; to prevent excessive loss of water

33. Plasmolysis – plant cell loses water, shrivel & plasma membrane pulls away from cell wall

34. Facilitated Diffusion: - involves diffusion of molecules that cannot diffuse easily across a membrane - uses a transport protein embedded in the membrane that forms a channel (pore) Sect 5.15

35. Active Transport - moves molecules against the [ ] gradient across a cell membrane requires energy (ATP) Many transport systems involve the movement of one substance out w/one substance into the cell Ex: Na-K pump Sect 5.18

36. Movement of Large Molecules/Substances Exocytosis – export of substances from the cytoplasm through vesicles that fuse w/the cell membrane Ex: tears, hormones Sect 5.19

37. Endocytosis – import of substances into the cytoplasm through vesicles formed by the cell membrane Phagocytosis – “cell eating” – engulfing large particles (bacteria) Pinocytosis – “cell drinking” – nonspecific engulfing droplets of liquids w/any dissolved solutes

38. Receptor-mediated endocytosis – highly specific on what is to be engulfed; has receptor proteins that pick up specific molecules When does this go wrong? Hypercholesterolemia – excessively high levels of cholesterol in the blood

39. LDL (low-density lipoprotein) vs HDL (high-density lipoprotein) - caused by faulty receptor-mediated endocytosis in liver cell membranes that do not remove excess cholesterol from the blood