How Cells Work

1. Chapter 4 How Cells Work

2. Energy Energy is central to life Universal relationship between energy and work Ultimate energy source = SUN Plants transform light energy into chemical energy (C6H12O6) Photosynthesis

3. What is energy? Energy = capacity to do work Work = movement against an opposing force

4. The Energy Currency Molecule Adenosine triphosphate, ATP Structure of ATP Adenosine Ribose + adenine 3 phosphate groups Negatively charged molecules that repel each other 2 HIGH ENERGY phosphate bonds

5. How do cells use ATP? Breakage of the last bond (release of a phosphate group) releases energy and allows the cell to do work ATP = STORED ENERGY = Potential ADP = CELL PERFORMED WORK = Kinetic

6. How Cells Use ATP

7. How do cells use ATP? From where does the energy to make ATP from ADP come? Covalent bonds in macromolecules! Cells recycle the ADP and phosphates This process requires ENERGY!! Analogous to recharging a battery: The components are in the battery – energy needs to be added to the battery to make it useable

8. Energy Reactions and Cycles Endergonic Reactions Require energy i.e. Synthesis of glucose from CO2 and water during photosynthesis Exergonic Reactions Release energy i.e. Breakdown of glucose to CO2 and water by aerobic respiration

10. Enzymes Reaction characteristics Exergonic reactions in living things may not occur very quickly Energy of Activation (high temperature, light) is needed to start the reaction Amount of energy needed to start a reaction Many different reactions are needed to complete a task These reactions are linked together

11. Activation Energy

12. Ways to Lower the Energy of Activation Enzymes Protein catalysts that lower the amount of energy needed to get the chemical reaction going They maintain their original chemical composition while causing a change in the substrate (reactant) The specific shape of the enzyme allows it to catalyze only one reaction Active site = place on the enzyme that binds substrate Since the enzyme does NOT change its shape, it is REUSABLE

13. Figure 5.5

14. Figure 5.6

15. Figure 5.7

16. Altering the Rate of an Enzymatic Reaction One can alter the rate by altering two key factors: 1. Temperature 2. pH 3. Coenzymes and Cofactors 4. Allosteric Regulators 5. Salt Concentration

17. Altering Temperature Gradual ? in temperature will INCREASE the rate of the reaction How? By an increase in the speed at which the molecules are moving This results in increased collisions of the enzyme and substrate Extremely low temperatures will SLOW DOWN or STOP the reaction Why? The enzyme and substrate are moving too slow to collide Extremely high temperatures will STOP the reaction Why? Because the enzyme will be denatured!

18. Altering pH Alterations in pH will STOP the reaction because the enzyme will be denatured! Remember, a small pH change does NOT correlate with a small change in the pH of the environment!! Why? pH scale is logarithmic

19. Figure 5.8

20. Enzyme Questions The presence of an enzyme _____ the required energy of activation of a chemical reaction. Generally, as the amount of substrate is increased, the rate of the reaction _____. Raising the temperature to over 50C ___ the rate of an enzymatic reaction. Lowering the pH for an enzyme that works best in a highly acidic environment ___ the rate for the reaction.

21. Ways that substances can move across the PM Passive Process that does NOT require energy Includes: Diffusion Osmosis Active Process that DOES REQUIRE energy! Includes: Endocytosis Phagocytosis Pinocytosis Receptor-Mediated Endocytosis Exocytosis

22. How exactly do things move back and forth across a cell’s plasma membrane?? What are we looking at moving? Water, foodWhat are we looking at moving? Water, food

23. Selective Permeability Protein channels located in the plasma membrane act as channels Each channel passes only a certain kind of molecule (some are specific, some non-specific) Types of selective permeability Selective Diffusion Facilitated Diffusion Active Transport

24. Selective Diffusion Movement of molecules from high concentration to low concentration Channels may act as ‘open doors’ Example includes ion channels Ion channels allow passage of any ion that can fit in the channel Essential roles in nervous system signaling

25. Diffusion Oxygen, Carbon dioxide (CO2) and lipids can pass across the PM using diffusion One way in which water and other substances can move across the PM RANDOM movement of molecules in a solution from regions of HIGH concentration to regions of LOW concentration HIGH low Random movement occurs until equilibration occurs Until there is NO NET MOVEMENT in any particular direction NOTE: Individual molecules are still moving – but there is no overall directionality!

28. DiffusionTerms to know: Concentration gradient A system that is imposed on a solution by molecules present in that solution. Ex. Sugar in water When sugar is dropped in water, the sugar molecules break up and dissolve over time. The individual sugar molecules moving into the water move DOWN their concentration gradient – they are moving from the cube of sugar to spread out in the water where there is no sugar.

29. Osmosis Movement of WATER ONLY across the PM from the side with more water (less solute) to the side with less water (more solute) Water passes into and out of a cell down its concentration gradient (DIFFUSION) DIFFERENT from diffusion in that water movement depends upon the concentration of other substances in solution

30. OsmosisTerms to know: Osmotic concentration Concentration of ALL molecules dissolved in a solution Hypertonic The solution with higher solute concentration Hypotonic The solution with lower solute concentration Isotonic Solutions are isotonic when the solute concentrations of both are equal

31. Figure 4.27

32. OsmosisOsmotic pressure Generated by movement of water into a cell by osmosis Ex. Red blood cell, Figure 4.28

33. Osmosis

34. What is another way that cells can take in food and liquids? Diffusion Osmosis Endocytosis Phagocytosis Pinocytosis Receptor-Mediated Endocytosis Exocytosis

35. Endocytosis Allows for BULK PASSAGE of food and liquids INTO the cell Two types: Phagocytosis “Cell eating” Pinocytosis “Cell drinking” The PM engulfs the particle(s) forming a vesicle thus allowing a means of entry into the cell

36. EndocytosisPhagocytosis: “Cell eating” Material that the cell takes in may include particulate, digested particles or other fragments of organic matter Pinocytosis: “Cell drinking” Material that the cell takes in is liquid

37. Phagocytosis and Pinocytosis

38. Endocytosis, continued Rates of endocytosis vary among cells! Ex. Muscle cells during exercise

39. Exocytosis Process by which material is discharged from the cell Material to be discharged is packaged into vesicles inside the cell (by what organelle?) Vesicles then make they way (along what?) to the plasma membrane for secretion into the cell exterior Golgi, cytoskeletonGolgi, cytoskeleton

40. Exocytosis

41. Problems with endocytosis Expensive for the cell Cell uses a lot of its membrane to form vesicles Non selective Anything can enter the cell through

42. Everyday ScienceHypercholesterolemia Human genetic disease Receptors are normally embedded in the PM In patients with HC, the receptors are not help in place by clathrin This results in a failure of cholesterol uptake into the cell (failure of the mouse-trap triggering mechanism) thus leaving the cholesterol to travel though the bloodstream and bind to arteries

44. Discussion Question Do you think muscle cells have a higher or lower rate of endocytosis during exercise?