Chapter 4 Energy and Metabolism

1. Chapter 4 Energy and Metabolism

2. 4.1 A Toast to Alcohol Dehydrogenase • Binge drinking is currently the most serious drug problem on college campuses • Alcohol dehydrogenase (ADH), helps break down ethanol and other toxic compounds • Ethanol and its breakdown products damage liver cells, leading to alcoholic hepatitis or cirrhosis of the liver

3. Alcohol Dehydrogenase

4. 4.2 Life Runs on Energy • Energy • The capacity to do work • Work occurs as a result of energy transfers • Example: A plant cell powers glucose synthesis by absorbing light energy from the sun • Some energy is lost during every transfer or conversion

5. Laws of Thermodynamics • First law of thermodynamics • Energy cannot be created or destroyed • Energy can be converted from one form to another and transferred between objects or systems • Second law of thermodynamics • Energy tends to disperse spontaneously • Some energy disperses at each energy transfer, usually in the form of heat

6. One-Way Flow of Energy • Living things maintain their organization by harvesting energy from someplace else • Energy flows in one direction through the biosphere (starting mainly from the sun) then into and out of ecosystems • Energy in chemical bonds is a type of potential energy

7. Potential Energy

8. Material Recycle • Energy inputs drive a cycling of materials among producers and consumers • Producers and then consumers use energy to assemble, rearrange, and break down organic molecules that cycle among organisms throughout ecosystems

9. One-Way Flow of Energy A) Energy In. Sunlight energy reaches environments on Earth. Producers in those environments capture some of the energy and convert it to other forms that can drive cellular work. sunlight energy Producers B) Some of the energy captured by producers ends up in the tissues of consumers. Nutrient Cycling Consumers C) Energy Out. With each energy transfer, some energy escapes into the environment, mainly as heat. Living things do not use heat to drive cellular work, so energy flows through the world of life in one direction overall.

10. 4.3 Energy in the Molecules of Life • Cells store and retrieve energy by making and breaking chemical bonds in metabolic reactions • Some reactions require a net input of energy – others end with a net release of energy

11. Chemical Reactions • Reaction • Process of chemical change • Reactant • Molecule that enters a reaction • Product • A molecule remaining at the end of a reaction

12. Energy Inputs and Outputsin Chemical Reactions • Chemical bonds hold energy – the amount depends on which elements take part in the bond • Cells store energy in chemical bonds by running energy-requiring reactions, and access energy by running energy-releasing reactions

13. Energy Inputs and Outputsin Chemical Reactions 6 glucose C6H12O2 oxygen O2 Energy A) energy in B) energy out 6 6 carbon dioxide CO2 water H2O

14. Why the Earth Doesn’t Go Up in Flames • Molecules of life release energy when combined with oxygen, but not spontaneously – energy is required to start even energy-releasing reactions • Activation energy • Minimum amount of energy required to start a reaction

15. Activation Energy Reactants: 2 H2 + O2 Activation energy Difference between energy of reactants and products Products: 2H2O Energy Time

16. Energy In, Energy Out • Cells store energy by running energy-requiring reactions that build organic compounds • Cells harvest energy by running energy-releasing reactions that break the bonds of organic compounds

17. Energy In, Energy Out small molecules (e.g., carbon dioxide, water) organic compounds (carbohydrates, fats, proteins) energy-requiring reactions A) Cells store energy in the chemical bonds of organic compounds. small molecules (e.g., carbon dioxide, water) organic compounds (carbohydrates, fats, proteins) energy-releasing reactions B) Cells retrieve energy stored in the chemical bonds of organic compounds. Figure 4-6 p67

18. 4.4 How Enzymes Work • Enzymes make chemical reactions proceed much faster than they would on their own • Enzyme • Protein or RNA that speeds a reaction without being changed by it • Substrate • Reactant molecule specifically acted upon by an enzyme • An enzyme’s particular substrates bind at its active site

19. enzyme substrates A) An active site is complementary in shape, size, polarity, and charge with the enzyme’s substrates. active site B) The active site squeezes substrates together, influences their charge, or causes some other change that lowers activation energy. How an active site works C) The reaction proceeds and the product leaves the active site. The enzyme is unchanged, so it can work again and again.

20. How an active site works D) For simplicity, enzymes and active sites are often depicted as blobs or geometric shapes. This model shows the actual contours of an active site in an enzyme (hexokinase) that adds a phosphate group to six-carbon sugars. A phosphate group is meeting up with a glucose molecule in the active site.

21. Factors That Influence Enzyme Activity • Regulatory molecules affect an enzyme by binding directly to its active site; or elsewhere on the enzyme • Each enzyme works best within a characteristic range of temperature, pH, and salt concentration • When conditions break hydrogen bonds, an enzyme changes its characteristic shape (denatures), and stops working

22. Regulatory molecule binding to enzymes substrates enzyme regulatory molecules

23. Enzymes and pH

24. Enzymes and Temperature

25. Cofactors • Cofactor • A metal ion or a coenzyme that associates with an enzyme and is necessary for its function • Coenzyme • An organic cofactor • Unlike enzymes, it may be modified by a reaction • Example: coenzyme NAD+ + electrons + H → NADH

26. ATP and Phosphorylation • ATP functions as a coenzyme in many reactions • When a phosphate group is transferred to or from a nucleotide, energy is transferred along with it • Phosphate-group transfers (phosphorylation) to and from ATP couple energy-releasing reactions with energy-requiring ones

27. Phosphorylation

28. Metabolic Pathways • Cells concentrate, convert, and dispose of most substances in enzyme-mediated reaction sequences • Metabolic pathway • Series of enzyme-mediated reactions by which cells build, remodel, or break down an organic molecule

29. Linear and Cyclic Metabolic Pathways

30. Controlling Metabolism • Various controls over enzymes allow cells to conserve energy and resources by producing only what they require • Concentrations of reactants and products • Feedback inhibition • Feedback inhibition • Mechanism by which a change that results from some activity decreases or stops the activity

31. Feedback Inhibition reactant X enzyme 1 intermediate enzyme 2 intermediate enzyme 3 product

32. reactant X enzyme 1 intermediate enzyme 2 intermediate enzyme 3 product Stepped Art Figure 4-10 p70

33. Electron Transfers • Electron transfer chains allow cells to harvest energy in manageable increments • Electron transfer chain • An array of membrane-bound enzymes and other molecules that accept and give up electrons in sequence

34. Uncontrolled Energy Release glucose + oxygen carbon dioxide + water A) Glucose and oxygen react (burn) when exposed to a spark. Energy is released all at once as light and heat when carbon dioxide and water form.

35. Controlled Energy Release 1 glucose + oxygen H+ 2 carbon dioxide + water 3

36. ANIMATION: Allosteric inhibition

37. 4.5 Diffusion and Membranes • Diffusion • Spontaneous spreading of molecules or ions through a liquid or gas

38. Diffusion Rate • How quickly a particular solute diffuses through a particular solution depends on five factors: 1. Size 2. Temperature 3. Concentration 4. Charge 5. Pressure

39. Concentration Gradient • Concentration • The number of molecules or ions per unit volume of a fluid • Concentration gradient • Difference in concentration of a substance between adjoining regions of fluid

40. Selective permeability of lipid bilayers carbon dioxide ions; glucose and other polar organic molecules gases oxygen lipid bilayer water

41. Tonicity • When fluids on either side of a selectively permeable membrane differ in solute concentration, water diffuses across the membrane in a direction that depends on tonicity: • Hypotonic:Low solute concentration relative to another fluid • Hypertonic: High solute concentration relative to another fluid • Isotonic: Same solute concentration relative to another fluid

42. Osmosis • When a selectively permeable membrane separates two fluids that are not isotonic, water will diffuse from the hypotonic fluid into the hypertonic one • Osmosis • Diffusion of water across a selectively permeable membrane between two fluids that are not isotonic • If extracellular fluid is not isotonic, cell volume changes • Cells in hypertonic fluid shrink • Cells in hypotonic fluid swell

43. Osmosis selectively permeable membrane

44. Effects of tonicity in human red blood cells A) Red blood cells immersed in an isotonic solution do not change in volume. The fluid portion of blood is normally isotonic with cytoplasm. B) Red blood cells immersed in a hypertonic solution shrivel up as water diffuses out of them. C) Red blood cells immersed in a hypotonic solution swell up as water diffuses into them.

45. Osmosis and Turgor • In plant cells, turgor counters osmosis • Turgor • Pressure that a fluid exerts against a wall, membrane, or other structure that contains it • Osmosis continues until two fluids are isotonic, or until pressure against the hypertonic fluid counters the movement

46. Effects of tonicity in plant cells D) Osmotic pressure keeps plant parts erect. These cells in an iris petal are plump with cytoplasm. E) Cells from a wilted iris petal. The cytoplasm shrank, and the plasma membrane has pulled away from the cell wall.

47. 3D ANIMATION: Osmosis

48. ANIMATION: Selective Permeability

49. 4.6 Membrane Crossing Mechanisms • Gases, water, and small nonpolar molecules can diffuse across a lipid bilayer • Most other molecules and ions cross only with the help of transport proteins • Each type of transport protein moves a specific ion or molecule across a membrane

50. Passive and Active Transport • Passive transport • Concentration gradient drives a solute across a cell membrane through a transport protein • Requires no energy input • Example: glucose transporters • Active transport • A transport protein uses energy (ATP) to pump a solute across a cell membrane against its concentration gradient • Example: calcium pump