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BSC 114, Chapter 8

by: Hannah Tomlinson

BSC 114, Chapter 8 BSC 114

Hannah Tomlinson

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Intro to Metabolism
Principles Of Biology I
Kimberly Caldwell
Class Notes
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This 5 page Class Notes was uploaded by Hannah Tomlinson on Sunday September 25, 2016. The Class Notes belongs to BSC 114 at University of Alabama - Tuscaloosa taught by Kimberly Caldwell in Fall 2016. Since its upload, it has received 14 views. For similar materials see Principles Of Biology I in Biology at University of Alabama - Tuscaloosa.


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Date Created: 09/25/16
9/19 Chapter 8: Introduction to Metabolism Metabolism  All the chemical changes that happen in an organism  Metabolic pathways begin with a specific molecule, which is then altered in a series of defined steps. This results in a certain product.  Enzymes: serve as catalysts (chemical agents that change the rate of a reaction without being consumed by the reaction)  2 types of pathways metabolism can follow -Catabolic: breaks down complex molecules to simpler compounds (from proteins to amino acids) -Anabolic: consume energy to build complex molecules from simpler ones (synthesis of proteins from amino acids) -These work together in order to make energy coupling.  Energy coupling: interaction between catabolic and anabolic pathways Energy  Energy= capacity to do work  Energy is the ability to rearrange a collection of matter (e.g.: your cells expend energy moving substances across membranes) Forms of Energy  Kinetic energy: when energy is associated with the relative motion of objects  Potential energy: an object not presently moving may still possess energy (this is not kinetic energy)  Chemical energy: the potential energy available for release in a chemical reaction -Ex.- molecules store energy because of the atom arrangement -Catabolic pathways release energy by breaking down complex molecules (through hydrolysis) How does energy work in cells?  Thermodynamics: the study of energy transformation that occur in a collection of matter  2 important laws of thermodynamics apply to biological systems -1 law of thermodynamics -2ndlaw of thermodynamics st 1 Law  Energy can be transferred and transformed but it cannot be created or destroyed  AKA conservation of energy -e.g.: an electric company does not produce energy but it converts it to a form we can use -e.g.: 2 ndLaw  Every energy transfer of transformation increases the entropy of the universe -Entropy is a measure of disorder -Entropy is less apparent tin biological systems because it takes the form of heat -Biological systems are not very efficient because of a great deal of energy is dispersed or lost through heat  Heat is energy in a random state, we have not created or destroyed energy. Applying thermodynamics to biological reactions  Thermodynamics apply to the whole universe  Biologists want to understand metabolic reactions  One way of determining whether metabolic reactions are spontaneous is by measuring free energy.  Free energy (G) is the portion that is available to perform work Free Energy  The change in free energy (delta G) can be calculated using the formula: Total energy – absolute temperature (Kelvin) multiplied by system’s entropy Change in Free Energy  When we know the change in G for a process, we can predict whether the reaction will be spontaneous (without outside energy)  Spontaneous does not necessarily mean fast, simply that it can occur eventually without energy -Spontaneous reactions have negative change in G value -Process that have a positive or zero change in G are never spontaneous Why do biologists care about change in free energy?  Gives us the power to predict which kinds of changes can happen “without assistance”  Important for metabolism because we need to know which reactions can supply energy to do work for other reactions in a cell. Maximum Stability  Max stability=equilibrium  Most chemical reactions are reversible (and proceed forward and backward at the same rate)  As a reaction proceeds toward equilibrium, the mixture of reactants and products decreases and delta G approaches zero Classification of free energy changes and metabolism  Exergonic: reactions proceed with a net release of free energy (“energy outward”) and delta G is negative  Endergonic: reactions absorb free energy from the environment (“energy inward”) and delta G is positive Cellular Respiration  C 6 12+6O yie2ds 6CO + 6H2O 2  For every 180 grams of glucose broken down by cellular respiration, 686 kcal/mol of energy are made available for work  Delta G = -686 kcal/mol ATP  The source of energy that drives cellular work is ATP (adenosine triphosphate)  Structurally similar to one type of nucleotide found in nucleic acid -Adenine nitrogenous base -Ribose sugar -3 phosphate groups  The energy of ATP is stored in the bonds between the 3 phosphate groups  When the bonds are broken, a large amount of energy is released How ATP performs work  The triphosphate tail is highly unstable  When water hydrolyzes the terminal phosphate bond, a molecule of inorganic phosphate (Pi) is removed  ATP hydrolysis to ADP is exergonic and releases energy  ATP + H O2yields ADP + P 1  Delta G=-7.3 kcal/mol What happens to the phosphate?  The phosphate group is transferred to some other molecule with the help of an enzyme  The molecule that receives the phosphate is phosphorylated -This molecule is energized and performs work  E.g.: ATP powers the movement of muscles by transferring phosphate to contractile proteins How ATP hydrolysis of ATP performs work  With the help of specific enzymes, the cell is able to use the energy released by ATP hydrolysis directly to drive chemical reactions that, by themselves, are endergonic  This is called energy coupling ATP can be regenerated  ATP is regenerated by the addition of phosphate to ADP  The ATP cycle can work at an incredible pace  E.g.: a working muscle recycles its entire pool of ATP about once each minute. That turnover represents 10 million molecules of ATP consumed and regenerated per second per cell Enzymes  Speed up the rate of reactions  Although a reaction may be spontaneous, it may take years for the hydrolysis to take place -The ending –ASE indicates an enzyme Enzyme Example  The hydrolysis of sucrose into glucose and fructose could take years sitting in sterile water at room temperature, but adding the enzyme sucrase will allow the hydrolysis to take place within seconds Characteristics of Enzymes  Proteins  Catalysts: chemical agents that change the rate of a reaction without being consumed by the reaction  Enzymes are critical ingredients to expedite spontaneous reactions  Lower the activation energy  Increase the rates of reactions  A chemical reaction involves breaking and making bonds. The bonds on existing reactants must be broken and new bonds formed, creating the products Activation Energy  The initial investment of energy for starting a reaction  The energy required to break bonds in the reactant molecules Substrates  The substance on which an enzyme will work  Enzymes are picky and will only react with certain molecules Enzymes and Substrates  There are many different enzymes and substrates  Enzymes actually bind to substrates  An enzyme increases the rate of reaction without becoming consumed in the process  A single enzyme molecule can act on 1,000 substrate molecules per second -Some enzymes are even faster Active Site of an Enzyme  Enzymes are typically big molecules  Usually only one part of the molecule is used in the reaction (the active site)  The active site -Is usually a pocket or groove on the surface of the protein -Is composed of only a few of the enzyme’s amino acid -The rest of the protein provides a framework that keeps the active site in an appropriate configuration Factors Affecting Enzyme Activity  Just as there is an optimal environment for our cells, enzymes have optimal conditions in which they perform at their best  3 groups of factors affect enzyme activity -Environmental factors -Cofactors -Enzyme inhibitors Environmental Factors  Temperature  pH  Salt concentration Cofactors  Non-protein helpers for catalytic activity  E.g.: inorganic cofactors (metal atoms) -Zinc -Iron -Copper  E.g.: organic molecules -Coenzymes (vitamins) Enzyme Inhibitors  Competitive inhibitors -Resemble the substrate and compete for active site -One way to get around this problem: increase amount of substrate so that there is more substrate than the competitive inhibitor  Noncompetitive inhibitors -Binds to the enzyme at a location away from the active site but alters the conformation of the enzyme so that the active site is no longer functional


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