What Is Energy? Energy is the capacity to do work. Synthesizing molecules Moving objects Generating heat and light Types of Kinetic: of movement otential: stored First Law of Thermodynamics Energy cannot be created nor destroyed, but it can change its form. Example: potential in gasoline can be converted to kinetic in a car (but the is not lost) Second Law of Thermodynamics When is converted from one form to another, the amount of useful decreases. No conversion is 100% efficient. Example: more potential is in the gasoline than is transferred to the kinetic of the car moving Some E is released as heat (a less useful form ) but the total E is maintained. Matter tends to become less organized. There is a continual decrease in useful, and a build up of heat and other nonuseful forms of. Entropy: spontaneous reduction in ordered forms of, and an increase in randomness and disorder as reactions proceed Example: gasoline is made up of an eightcarbon molecule that is highly ordered When broken down to single carbons in CO 2, it is less ordered and more random. In order to keep useful flowing in ecosystems where plants and animals produce more random forms of, new must be brought in. i.e., in any system, in order to maintain order, we need to continually input E SUN!!!!!!!!! How Does Energy Flow In Chemical Reactions? Chemical reaction: conversion of one set of chemical substances () into another () A B C D Two types of chemical reactions 1) Those that need E input (endergonic) 2) Those that release E (exergonic) 1
Metabolism: All the chemical reactions of the body Catabolism releasing (exergonic) decomposition reax Breaks apart bonds produces smaller molecules Anabolism storing (endergonic) synthesis reax requires input production of protein or fat driven by that catabolism releases Endergonic reaction: a reaction that requires input from an outside source; the product(s) contain more than the Energy is used E.g., Dehydration synthesis A.A. input A.A. rotein roducts H2O Endergonic Reactions hotosynthesis requires. Glucose Oxygen have more than the Exergonic reaction: a reaction that releases E; the contain less than the Energy is released 6 CO 2 6 H 2 O (carbon (water) dioxide) C 6 H 12 O 6 6 O 2 (glucose) (oxygen) released Fig. 5-5 Exergonic reaction: Burning glucose releases. Mitochondria roduces AT C 6 H 12 O 6 6 O 2 (glucose) (oxygen) released 6 CO 2 (carbon dioxide) 6 H 2 O (water) Endergonic and Exergonic Reactions Endergonic reactions require input of to proceed roducts contain more than Synthesis Reax Exergonic reactions release as they proceed roducts contain less than Decomposition Reax Fig. 5-4 4-26 2
Coupled Reactions: AT Cells require constant inputs of to buck entropy and remain highly organized Do this by coupling endergonic reactions to exergonic reactions Use AT AT is the principal carrier in cells. AT stores in its phosphate bonds AT s phosphate bonds can be broken yielding AD, phosphate, and. This is transferred to an -requiring reaction (endergonic reaction) 1. Most endergonic reactions in body make AT 2. An exergonic reaction breaks down AT - the universal carrier Make AT 4-27 AT is made from AD (adenosine diphosphate) and phosphate plus released from an exergonic reaction (e.g., glucose breakdown) in a cell. Breakdown of AT releases. A A A AT AT A AD phosphate AD phosphate Fig. 5-7 Fig. 5-8 To summarize: Exergonic reactions (e.g., glucose breakdown) drive endergonic reactions (e.g., the conversion of AD to AT). AT moves to different parts of cell and is broken down exergonically to liberate its to drive endergonic reactions. Summary: Coupled reactions glucose exergonic (glucose breakdown) CO 2 H 2 O heat A endergonic (AT synthesis) exergonic (AT breakdown) protein endergonic (protein synthesis) A amino acids Fig. 5-9 3
How Energy Carried Between Coupled Reactions Electron carriers also transport within cells. Besides AT, other carrier molecules transport within a cell. Electron carriers capture energetic electrons transferred by some exergonic reaction. Energized electron carriers then donate these -containing electrons to endergonic reactions. Common electron carriers are NAD and FAD. high- low- e energized NADH depleted NAD H e high- low- Fig. 5-11 Metabolic pathways: sequence of cellular reactions (e.g., photosynthesis and glycolysis) All reactions require an initial input of. The initial input to a chemical reaction is called the activation. Initial reactant Intermediates Final ATHWAY 1 A B C D E high Activation needed to ignite glucose Energy level of Activation captured from sunlight glucose glucose O 2 ATHWAY 2 F G content of molecules CO 2 H 2O CO 2 H 2O Energy level of low (a) progress of reaction Burning glucose (sugar): an exergonic reaction (b) progress of reaction hotosynthesis: an endergonic reaction Fig. 5-12 Fig. 5-6 Enzymes!! How Cells Control Their Metabolic Reactions At body temperature, many spontaneous reactions proceed too slowly to sustain life. A reaction can be controlled by controlling its activation (the needed to start the reaction). At body temperature, reactions occur too slowly because their activation energies are too high. Molecules called catalysts (enzymes) help lower the activation needed for a reax Enzymes are catalysts that reduce activation level. They speed up a chemical reactions high content of Activation without catalyst Activation with catalyst molecules low progress of reaction 4
Three important principles about all catalysts 1. Enzymes speed up chemical reactions. - reactions that would occur anyway, if their activation could be surmounted. 2. Enzymes are specific work on specific molecules to produce a specific product 3. Catalysts are not altered by the reaction - can be reused over and over Enzyme Structure and Action Substrate approaches active site on enzyme molecule Substrate binds to active site forming enzyme-substrate complex highly specific fit enzyme-substrate specificity Reaction released Enzyme remains unchanged and is ready to repeat the process 2-26 Enzymatic Reaction Steps How does an enzyme catalyze a reaction? Substrates enter the enzyme s active site. Substrates enter an enzyme s active site, changing both of their shapes. The chemical bonds are altered in the substrates, promoting the reaction. The substrates change into a new form that will not fit the active site, and so are released. Sucrose (substrate) 1 Enzyme and O substrate Active site Sucrase (enzyme) 2 Enzyme substrate complex O Glucose Fructose 3 Enzyme and reaction Figure 2.27 2-28 How enzymes work substrates enzyme 1 Substrates enter the active site in a specific orientation active site of enzyme lease note that due to differing operating systems, some animations will not appear until the presentation is viewed in resentation Mode (Slide Show view). You may see blank slides in the Normal or Slide Sorter views. All animations will appear after viewing in resentation Mode and playing each animation. Most animations will require the latest version of the Flash layer, which is available at http://get.adobe.com/flashplayer. 3 The substrates, bonded 2 The substrates and together, leave the enzyme; active site change shape, the enzyme is ready for a promoting a reaction new set of substrates between the substrates Fig. 5-14 5
lease note that due to differing operating systems, some animations will not appear until the presentation is viewed in resentation Mode (Slide Show view). You may see blank slides in the Normal or Slide Sorter views. All animations will appear after viewing in resentation Mode and playing each animation. Most animations will require the latest version of the Flash layer, which is available at http://get.adobe.com/flashplayer. Cells regulate metabolism by controlling enzymes. Allosteric regulation can increase or decrease enzyme activity. In allosteric regulation, an enzyme s activity is modified by a regulator molecule. The regulator molecule binds to a special regulatory site on the enzyme (separate from the enzyme s active site). Binding of regulator molecule modifies the active site on enzyme, causing the enzyme to become more or less able to bind substrates. i.e., allosteric regulation can promote or inhibit enzyme activity Enzyme structure Allosteric inhibition substrate active site enzyme Many enzymes have both active sites and allosteric regulatory sites An allosteric regulator molecule causes the active site to change shape, so the substrate no longer fits (a) Enzyme structure allosteric regulatory site Fig. 5-15a Allosteric inhibition allosteric regulator molecule Fig. 5-15b Enzymatic Action: Important oints!! Competitive inhibition A competitive inhibitor molecule occupies the active site and blocks entry of the substrate Reusability of enzymes Astonishing speed one enzyme molecule can consume millions of substrate molecules per minute Factors that change enzyme shape ph and temperature Fig. 5-16 2-36 6
Metabolic pathways: sequence of cellular reactions (e.g., photosynthesis and glycolysis) Initial reactant Intermediates Final ATHWAY 1 A C E B D enzyme 1 enzyme 2 enzyme 3 enzyme 4 ATHWAY 2 F G enzyme 5 enzyme 6 lease note that due to differing operating systems, some animations will not appear until the presentation is viewed in resentation Mode (Slide Show view). You may see blank slides in the Normal or Slide Sorter views. All animations will appear after viewing in resentation Mode and playing each animation. Most animations will require the latest version of the Flash layer, which is available at http://get.adobe.com/flashplayer. 7