Presentation on theme: "Energy can be converted from one form to another form"— Presentation transcript:
1 Chapter 5: Ground Rules of Metabolism – Energy Flow, Metabolic Pathways, Enzymes
2 Energy can be converted from one form to another form Energy can be converted from one form to another form. Many living organisms take advantage of this. For example, plants use carbon dioxide, water, and energy from the sun to produce glucose, a molecule that can be broken down to provide energy for cellular reactions. Other organisms, such as ourselves, consume plants and other organisms, and the energy stored in some of the their molecules can be used to fuel cellular reactions in our cells.You also take advantage of energy conversion when you drive your car. Energy stored in gasoline molecules is converted to movement when you press on the accelerator.globalchange.umich.edu
3 What Is Energy? Energy is the capacity to do work Work is a force acting on an object that causes the object to move
4 What Is Energy? Chemical energy The energy that powers life The objects that move are electrons, which reposition during chemical reactions
5 Laws of Thermodynamics 2 fundamental types of energyKinetic energythe energy of movemente.g. light, heat, electricity, moving objectsPotential energystored energye.g. chemical energy in bonds, electrical charge in a battery, a rock at the top of a hill
6 FIGURE 6-1 From potential to kinetic energy Perched atop an ice floe, the body of the penguin has potential energy, because the ice is much higher than the ocean. As it dives, the potential energy is converted to the kinetic energy of motion of the penguin's body. Finally, some of this kinetic energy transferred to the water causes the water to splash and ripple.
7 The Laws of Thermodynamics describe the availability and usefulness of energy
8 First Law of Thermodynamics Energy can neither be created nor destroyedTotal amount of energy within a system remains constant unless energy is added or removed from system
9 Second Law of Thermodynamics Amount of useful energy decreases when energy is converted from one form to anotherEx. When glucose is broken down in the body to get energy, not all of the stored energy in that molecule is used. Some of the energy is lost in the form of heat, which is not a usable form of energy for the organism.As energy is converted from one form to another, Entropy (disorder) increases
10 FIGURE 6-2 Energy conversions result in a loss of useful energy FIGURE 6-2 Energy conversions result in a loss of useful energy. There are 100 units of chemical energy stored in the gas can. However, when that fuel is burned, only 25 units of that energy is converted to kinetic energy so that the car can move. The other 75 units of energy is lost in the form of heat. The second law of thermodynamics states that as energy is converted from one form to another, usable energy decreases and entropy increases.
11 EntropyA cell works similarly to keeping your room clean. In a cell and in keeping a neat room, to keep things organized and in their place, there must be a constant input of energy to counteract the effects of entropy (disorder). A cell must have a constant input of energy in order to function properly.
12 Energy of SunlightAutotrophic organisms, such as plants, acquire their energy from the sun. Heterotrophic organisms like the monkey above get energy by consuming other organisms.freefoto.compicturesindia.com
13 Chemical ReactionsProcesses that form or break chemical bonds between atomsChemical reactions convert reactants to productsReactants Products
14 Chemical ReactionsReactions can be categorized as exergonic or endergonic based on energy gain or loss
15 Exergonic Reactions Release energy Reactants contain more energy than products
17 Activation EnergyAll chemical rxns require an initial energy input (activation energy) to get startedElectrons of an atom repel other atoms and inhibit bond formation
18 FIGURE 6-6 Energy relations in exergonic reactions An exergonic ("downhill") reaction, such as burning sugar, proceeds from high-energy reactants (here, glucose and O2) to low-energy products (CO2 and H2O ). The energy difference between the chemical bonds of the reactants and products is released as heat. To start the reaction, however, an initial input of energy—the activation energy—is required.
19 Endergonic Reactions Require an input of energy Products contain more energy than reactants
21 Coupled Reactions Exergonic rxns drive endergonic rxns Energy-carrier moleculesused to transfer energy within cells
22 Energy Carrier Molecules Energy carrier molecules are only used within cells because they are unstablenewgeology.usmotherearthnews.com
23 ATP Adenosine triphosphate (ATP) most common energy carrying moleculeComposed of an adenosine molecule and 3 phosphates
24 ATP Energy stored in high-energy bond extending to last phosphate Heat is given off when ATP breaks into ADP (adenosine diphosphate) and P (phosphate)
25 ATP – Coupled Reactions Energy released when ATP is broken down into ADP + P is transferred to endergonic rxns through coupling
26 Electron CarriersEnergy can be transferred to electrons in glucose metabolism and photosynthesisElectron carriers transport high-energy electrons2 common e- carriers:Nicotinamide adenine dinucleotide (NAD+)Flavin adenine dinucleotide (FAD+)
27 FIGURE 6-12 Electron carriers Low-energy electron-carrier molecules such as NAD+ pick up electrons generated by exergonic reactions and hold them in high-energy outer electron shells. Hydrogen ions are often picked up simultaneously. The electron is then transferred, with most of its energy, to another molecule to drive an endergonic reaction, often the synthesis of ATP.
28 Metabolism Sum of all chemical rxns in a cell Many cellular reactions are linked through metabolic pathwaysThere are often many reactions that must occur in a metabolic pathway to get the final product.
29 Metabolic Pathways Endergonic rxns are coupled with exergonic rxns 2. Energy-carrier molecules capture energy and transfer it between rxns3. Chemical rxns are regulated through enzymes
30 Spontaneous Reactions Spontaneous rxns proceed too slowly to sustain lifeRxn speed is generally determined by the activation energy requiredRxns with low activation energies proceed rapidly at body temperatureRxns with high activation energies (e.g. sugar breakdown) move very slowly at body temperatureThe activation energy is the energy required to force two atoms together in a chemical bond. The electrons of each atom repel each other and must be forced together in order to react. Even spontaneous reaction have an activation energy.
31 EnzymesProteins that catalyze (speed up) chemical rxns in cells
32 Catalysts Reduce Activation Energy Catalysts speed up rate of a chemical rxn without themselves being used upCatalysts speed up spontaneous rxns by reducing activation energy
33 Catalytic ConvertersCatalytic converters in cars facilitate the conversion of carbon monoxide to carbon dioxideOctane + oxygen carbon dioxide + water + energy + carbon monoxide(poisonous)
34 Catalytic ConvertersCatalyst in catalytic converter speeds carbon monoxide conversionCarbon monoxide + oxygen carbon dioxide + energy
35 FIGURE 6-14 Catalysts such as enzymes lower activation energy A high activation energy (black curve) means that reactant molecules must collide very forcefully in order to react. Catalysts lower the activation energy of a reaction (red curve), so a much higher proportion of molecules move fast enough to react when they collide. Therefore, the reaction proceeds much more rapidly. Enzymes are protein catalysts for biological reactions.
36 Enzymes Are Biological Catalysts Enzymes orient, distort, and reconfigure molecules in process of lowering activation energyEnzymes differ from non-biological catalysts b/c:Are specific for molecules they catalyzeActivity is often enhanced or suppressed by their reactants or products
37 Enzyme Structure Have a pocket called an active site Reactants (substrates) bind to active siteDistinctive shape of active site is complementary and specific to substrateActive site amino acids bind to substrate and distort bonds to facilitate a reaction
38 Enzyme Structure Three steps of an enzyme catalyst Substrates enter active site in a specific orientation2. Upon binding, substrates and enzyme change shape to promote a rxn3. Products of rxn leave the active site- leave enzyme ready for another catalysis
39 FIGURE 6-15 The cycle of enzyme-substrate interactions As you look at this figure, imagine the opposite type of reaction as well, in which an enzyme binds to a single molecule and causes it to dissociate into two smaller molecules.
40 Cells Regulate Metabolism One enzyme usually catalyzes a single step in a chain of metabolic rxns
41 Control of Metabolic Pathways Control of enzyme synthesis regulates availabilityEnzyme synthesized only when needed2. Some enzymes are inactive when synthesized and must be “turned on” to be activeEnzyme pepsin – found in stomach – only activated when stomach acid increasesMade in the inactive form to prevent self-digesting3. Small organic molecules can bind to enzymes and enhance/inhibit activity (allosteric regulation)
42 FIGURE 6-16 Some enzymes are controlled by allosteric regulation (a) Many enzymes have an active site and an allosteric regulatory site on different parts of the molecule. (b) When enzymes are inhibited by allosteric regulation, binding by a regulator molecule alters the active site so the enzyme is less compatible with its substrate.
43 Control of Metabolic Pathways Adequate amounts of formed product inhibit enzyme activity (feedback inhibition)
44 Drugs and PoisonsDrugs and poisons often inhibit enzymes by competing w/natural substrate for active siteKnown as competitive inhibition
45 Environmental Conditions Most enzymes function optimally only within a very narrow range of conditions3D structure of an enzyme is sensitive to pH, salts, temperature, and presence of coenzymes
46 FIGURE 6-19a Enzymes function best within narrow ranges of pH and temperature. The enzyme pepsin is found in the stomach and works to break down proteins. Salivary amylase is an enzyme that is involved in the digestion of starch. Notice that pepsin functions best at a pH of 2, and salivary amylase works best around a pH of 7.
47 FIGURE 6-19b Enzymes function best within narrow ranges of pH and temperature.