Energy & Metabolism. Two states of energy. Low and high potential energy 9/23/2016. Energy

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1 Energy & Metabolism Energy Life requires a constant flow of energy. Energy: The capacity to do work. Energy can be transferred to other objects or converted into different forms, but cannot be created or destroyed. Bioenergetics: study of energy in living systems. Many forms Mechanical (kinetic), heat, Electric current, light, Chemical, or radioactivity. Two states of energy Potential energy: stored energy. Kinetic energy: energy in motion. Low and high potential energy 1

2 Energy Many ways to measure energy. Most convenient way is to measure heat. In biology, the unit of heatis the kilocalorie(kcal). 1 kilocalorie = 1000 calories 1 calorie is the heat required to raise the temperature of 1 gram of water 1 degree Celsius. Calories? Small versus large calories. Small calories (used in biology): 1 kilocalorie = 1000 calories 1 calorie is the heat required to raise the temperature of 1 gramof water 1 degree Celsius. Large Calories (food labels) 1 kilocalorie = 1 Calorie 1 Calorie is the heat required to raise the temperature of 1 kilogramof water 1 degree Celsius. There is energy in molecules! Example from plants: CO2 and H2O have low potential energy. Expended energy through photosynthesis rearranges CO2and H2O atoms to form a glucose molecule (C6H12O6). Glucose has high potential energy. Energy is release when glucose is digested broken down into CO2and H2O. Burning food to release energy. The Sun Energy flows into our world from the sun. Convertedto potential energy through photosynthesis. 40 million billion calories per second! Only a fraction captured by plants. Stored in covalent bonds between atoms in a sugar molecule (glucose). 2

3 Free energy: energy available to do work in a system. For cellular metabolism: amount of energy available to break and subsequently form other bonds (chemical reactions). Energetic Reactions Endergonic: any reaction that requires an inputof energy. Converting low energy reactants into high energy products. Anabolic: builds molecules (like dehydration synthesis). Exergonic: conversion of high energy reactants into low energy products resulting in a releaseof energy. Catabolic: breaks down molecules (like hydrolysis). ATP Cells can t use the variety of energy released from carbs, proteins and lipids to do work. Must be convertedinto the type of energy all the parts of the cell run on: ATP. ATP powers almost every energy-requiring process in cells. ATP ATP: adenosine triphosphate. Composed of Ribose 5 carbon sugar Adenosine Chain of 3 phosphates Key to energy storage Bonds are unstable ADP 2 phosphates AMP 1 phosphate lowest energy form 3

4 20 ATP/ADP Cycle Energy from breaking down molecules is transferred to ATP, which then provides energy for building molecules. ATP is like a delivery truck for energy. Triphosphates are negatively charged and compressed together (high potential energy!): phosphoanhydride bonds. ATP not suitable for long term energy storage. Fats and carbohydrates better long term. Cells store only a few seconds worth of ATP. 4

5 Activation energy Extra energy required to destabilize existing bonds and initiate a chemical reaction. Catalystslower the amount of activation energy needed to break bonds and produce the chemical reaction. Reactions in cells are regulated by catalysts Enzymes are catalysts. Reducethe amount of activation energy needed for the reaction to occur. Makes chemical bonds more easily broken. They do this by putting the reactants under physical or chemical stress, making the bonds brittle. Enzymes are very specific to their reactants. Lactase breaks up lactose. Sucrase breaks up sucrose Enzymes may be suspended in the cytoplasm or attached to cell membranes and organelles. Multi-enzyme complexes subunits work together to form a molecular machine. Several enzymes catalyzing different steps of a sequence of reactions associated with each other in an assembly. Product can be delivered easily to next enzyme. Unwanted side reactions prevented. All reactions an be controlled as a unit. Enzyme function Rateof enzyme-catalyzed reaction depends on concentrations of substrate or enzyme. Any chemical or physical condition that affects the enzyme s 3 dimensional shape can change rate. Optimum temperature Optimum ph

6 Enzyme Inhibitors Inhibitor substance that binds to enzyme and decreases its activity. Competitiveinhibitor Competes with substrate for active site. Noncompetitive inhibitor Binds to enzyme at a site other than active site. Causes shape change that makes enzyme unable to bind substrate Biochemical pathways Reactions occur in a sequence. Product of one reaction is the substrate for the next. Many steps take place in organelles Feedback inhibition End-product of pathway binds to an allosteric site on enzyme that catalyzes first reaction in pathway. Shuts down pathway so raw materials and energy are not wasted. 35 6

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