Chapter 5 Ground Rules of Metabolism Sections 1-5

Transcription

1 Chapter 5 Ground Rules of Metabolism Sections 1-5

2 5.1 A Toast to Alcohol Dehydrogenase In the liver, the enzyme alcohol dehydrogenase breaks down toxic ethanol to acetaldehyde, an organic molecule even more toxic than ethanol Ethanol breakdown interferes with normal processes of metabolism as a result, fats tend to accumulate as large globules in the tissues of heavy drinkers Ethanol breakdown damages liver cells and can lead to alcoholic hepatitis and cirrhosis of the liver

3 Binge Drinking alcohol dehydrogenase

4 Alcoholic Liver Disease

5 3D ANIMATION: Process of Secretion

6 5.2 Energy in the World of Life Sustaining life s organization requires ongoing energy inputs Assembly of the molecules of life starts with energy input into living cells

7 Energy We define energy as the capacity to do work One form of energy can be converted to another Familiar forms of energy include light, heat, electricity, and motion (kinetic energy) The energy in chemical bonds is a type of potential energy, because it can be stored

8 Energy Disperses First law of thermodynamics Energy is neither created nor destroyed, but can be transferred from one form to another Second law of thermodynamics Entropy (a measure of dispersal of energy in a system) increases spontaneously The entropy of two atoms decreases when a bond forms between them (endergonic reaction)

9 Entropy heat energy Time Stepped Art Figure 5-2 p78

10 Energy Conversion Only about 10% of the energy in food goes toward building body mass, most is lost in energy conversions

11 Energy s One Way Flow The total amount of energy available in the universe to do work is always decreasing Each time energy is transferred, some energy escapes as heat (not useful for doing work) On Earth, energy flows from the sun, through producers, then consumers Living things need a constant input of energy

12 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. Figure 5-4 p79

13 ANIMATED FIGURE: One-way energy flow and materials cycling To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

14 Potential Energy

15 Take-Home Message: What is energy? Energy is the capacity to do work; it can be transferred between systems or converted from one form to another, but it cannot be created or destroyed Energy disperses spontaneously Some energy is lost during every transfer or conversion Organisms can maintain their complex organization only as long as they replenish themselves with energy they harvest from someplace else

16 ANIMATION: Total energy remains constant To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

17 5.3 Energy in the Molecules of Life All cells store and retrieve energy in chemical bonds of the molecules of life

18 Chemical Bond Energy Reaction A chemical change that occurs when atoms, ions, or molecules interact Reactant Atoms, ions, or molecules that enter a reaction Product Atoms, ions, or molecules remaining at the end of a reaction

19 Equations Represent Chemical Reactions

20 ANIMATED FIGURE: Chemical bookkeeping To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

21 Reactions Require or Release Energy We can predict whether a reaction requires or releases energy by comparing the bond energies of reactants with those of products Endergonic ( energy in ) Reactions that require a net input of energy Exergonic ( energy out ) Reactions that end with a net release of energy

22 Endergonic and Exergonic Reactions

23 Why the Earth Doesn t Go Up in Flames Activation energy The minimum amount of energy needed to get a reaction started Some reactions require a lot of activation energy, others do not

24 Free energy Activation Energy Reactants: 2H 2 O 2 Activation energy Difference between free energy of reactants and products Products: 2H 2 O Time

25 ANIMATED FIGURE: Activation energy To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

26 Energy In, Energy Out Cells store free energy by running endergonic reactions that build organic compounds Example: photosynthesis Cells harvest free energy by running exergonic reactions that break the bonds of organic compounds Example: aerobic respiration

27 Energy In

28 Energy Out

29 Take-Home Message: How do cells use energy? Activation energy is the minimum amount of energy required to start a chemical reaction Endergonic reactions cannot run without a net input of energy Exergonic reactions end with a net release of energy Cells store energy in chemical bonds by running endergonic reactions that build organic compounds; they harvest energy by breaking the bonds

30 ANIMATION: Energy changes in chemical work To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

31 5.4 How Enzymes Work Enzyme In a process called catalysis, an enzyme makes a specific reaction occur much faster than it would on its own Enzymes are not consumed or changed by participating in a reaction Most are proteins, some are RNA Substrate The specific reactant acted upon by an enzyme

32 The Transition State Enzymes lower the activation energy required to bring on the transition state, when substrate bonds break and reactions run spontaneously Active sites Locations on the enzyme molecule where substrates bind and reactions proceed Complementary in shape, size, polarity and charge to the substrate

33 Active Site of an Enzyme

34 active site enzyme A Like other enzymes, hexokinase has active sites that bind and alter specific substrates. A model of the whole enzyme is shown to the left. Figure 5-10a p82

35 reactant(s) B A close-up shows glucose and phosphate meeting in the active site. The microenvironment of the site favors a reaction between the two molecules. Figure 5-10b p82

36 product(s) c Here, the glucose has bonded with the phosphate. The product of this reaction, glucose-6-phosphate, is shown leaving the active site. Figure 5-10c p82

37 Mechanisms of Enzyme-Mediated Reactions Binding at enzyme active sites may bring on the transition state by four mechanisms Helping substrates get together Orienting substrates in positions that favor reaction Inducing a fit between enzyme and substrate (induced-fit model) Shutting out water molecules

38 Effects of Temperature, ph, and Salinity Raising the temperature boosts reaction rates by increasing a substrate s energy But very high temperatures denature enzymes Each enzyme has an optimum ph range In humans, most enzymes work at ph 6 to 8 Salt levels affect the hydrogen bonds that hold enzymes in their three-dimensional shape

39 rate of enzyme activity increases activity rate decreases as enzyme denatures Figure 5-12 p83

40 glycogen phosphorylase trypsin pepsin Figure 5-13 p83

41 Take-Home Message: How do enzymes work? Enzymes greatly enhance the rate of specific reactions. Binding at an enzyme s active site causes a substrate to reach its transition state. In this state, the substrate s bonds are at the breaking point Each enzyme works best at certain temperatures, ph, and salt concentration

42 ANIMATED FIGURE: Enzymes and their role in lowering activation energy To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

43 5.5 Metabolism: Organized, Enzyme-Mediated Reactions ATP, enzymes, and other molecules interact in organized pathways of metabolism (activities by which cells acquire and use energy)

44 Types of Metabolic Pathways A metabolic pathway is any series of enzyme-mediated reactions by which a cell builds, rearranges, or breaks down an organic substance Anabolic pathways build molecules Catabolic pathways break apart molecules Cyclic pathways regenerate a molecule from the first step

45 Controls Over Metabolism Concentrations of reactants or products can make reactions proceed forward or backward Feedback mechanisms can adjust enzyme production, or activate or inhibit enzymes Regulatory molecules can bind to an allosteric site to activate or inhibit enzymes Feedback inhibition

46 reactant X enzyme 1 intermediate enzyme 2 intermediate enzyme 3 product Stepped Art Figure 5-14 p84

47 regulatory molecules active site A Inactive form. substrate in active site B Active form. Figure 5-15 p84

48 ANIMATED FIGURE: Allosteric activation To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

49 Redox Reactions Oxidation-reduction reactions (paired reactions) A molecule that gives up electrons is oxidized A molecule that accepts electrons is reduced Coenzymes can accept molecules in redox reactions (also called electron transfers)

50 glucose + oxygen carbon dioxide + water Figure 5-16 p85

51 1 glucose + oxygen H + e 2 carbon dioxide + water 3 e Figure 5-16 p85

52 ANIMATED FIGURE: Controlling energy release To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

53 Take-Home Message: What are metabolic pathways? Metabolic pathways are sequences of enzyme-mediated reactions; some are biosynthetic; others are degradative Control mechanisms enhance or inhibit the activity of many enzymes; the adjustments help cells produce only what they require in any given interval Many metabolic pathways involve electron transfers, or redox reactions. Redox reactions occur in electron transfer chains; the chains are important sites of energy exchange in photosynthesis and aerobic respiration

54 ANIMATION: Types of reaction sequences To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE