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Transcript
Metabolisms and enzymes 4-11-16 What is a chemical reaction? • A chemical reaction is a process that forms or breaks the chemical bonds that hold atoms together – Chemical reactions convert one set of chemical substances, the reactants, into another set, the products Chemical energy • Primary energy source for metabolism is chemical energy stored in bonds – In animals = food molecules – In plants = photosynthesis • More bonds means more energy stored • Why fat is high in calories Photosynthesis and cellular respirantion • Photosynthesis – generates glucose – Sun energy transformed to energy carrier molecules like ATP and NADPH • Cellular respiration – consumes glucose – Eating glucose and breathing oxygen uses the energy in the bonds to generate energy carrier molecules Types of chemical reactions • All chemical reactions either release energy or require a net input of energy – Exergonic: releases energy – Endergonic: requires a net input of energy • The terms exothermic and endothermic relate to the overall exchange of heat during a process Exergonic reactions • Reactants have more energy than products • Energy is released in these reactions • Ex: Sugar + O2 CO2 + H2O • Releases energy and heat Endergonic reactions • Reactants have less energy than products • Synthesizing complex biological molecules requires energy Another way of seeing the reactions Metabolic pathways • The sum of all the chemical reactions inside a cell is its metabolism • Series of interconnected biochemical reactions • Convert a substrate molecule or molecules, through a series of metabolic intermediates, into a final product Initial reactant Intermediates End products PATHWAY 1 enzyme 1 enzyme 2 enzyme 3 enzyme 4 PATHWAY 2 enzyme 5 enzyme 6 Peppermint Types of pathways • Anabolic – require an input of energy – To synthesize complex molecules from simpler ones • Catabolic – generates energy – To break down complex molecules to simpler ones Chemical reactions in the body • Metabolic reactions are an “uphill battle” • Energy must be put in to drive reaction – True even if energy is released in reaction Potential energy • Minimum energy required = activation energy (Ea) Chemical reactions in the body • Ea can be overcome by increasing temperature – But we would cook! • At body temperature, metabolic reactions proceed too slowly to sustain life – And yet we live! • Nature has found a way around this What are catalysts? • Catalysts are molecules that speed up the rate of reaction w/out being used up or permanently altered What do catalysts do? • Catalysts speed up the reaction by lowering up the activation energy required for the reaction to begin Activation energy • A small amount of energy needed for exergonic reactions to occur (EA) • Bonds that will break and release energy need to get into the correct state • This contorted state is called the transition state – High-energy – Unstable What are enzymes? • • • • Biological catalysts Mainly proteins They speed up only exergonic reactions The majority catalyze one single reaction – Leaving similar substrates unchanged enzyme substrate enzymeproduct(s • Video Enzyme structures allow them to catalyze specific reactions • Each enzyme has a pocket called an active site into which one or more reactant molecules, called substrates, can enter Enzyme structures allow them to catalyze specific reactions • The amino acid sequence + folding of the protein chains distinctive shape and distribution of electrical charge Enzyme structures allow them to catalyze specific reactions • The distinctive shape of the active site is both complementary and specific to the substrate Enzyme structures allow them to catalyze specific reactions • In summary, active site amino acids bind to the substrate and distort bonds to facilitate a reaction Enzymes are proteins, so… • What is it called when a protein looses its shape and hence its function? • What can cause that? substrates active site of enzyme enzyme product Substrates enter the active site in a specific orientation The substrates, bonded together, leave the enzyme; the enzyme is ready for a new set of substrates The substrates and active site change shape, promoting a reaction between the substrates Cofactors and coenzymes • Many enzymes don’t work optimally, or even at all, unless bound to cofactors or coenzymes • Binding to these molecules promotes optimal conformation proper function • Cofactors are inorganic ions such as iron (Fe++) and magnesium (Mg++) – DNA polymerase requires zinc ions (Zn++) to function • Coenzymes are organic helper molecules – The most common sources of coenzymes are dietary vitamins – Some vitamins are precursors to coenzymes and others are coenzymes – Vitamin C is a coenzyme for multiple enzymes when building collagen Enzyme activity regulation • pH – Enzyme structure is distorted (denatured) when pH is too high or low Enzyme activity regulation • Salt concentration – Salt ions can bind with key amino acids in enzymes, influencing three-dimensional structure and destroying function Enzyme activity regulation • Temperature – Low temperatures slow down molecular movement – High temperatures cause enzyme shape to be altered, destroying function – Most enzymes function optimally only within a very narrow range of these conditions fast For trypsin, maximum activity occurs at about pH 8 For pepsin, maximum activity occurs at about pH 2 For most cellular enzymes, maximum activity occurs at about pH 7.4 rate of reaction slow 0 1 2 3 4 5 6 Effect of pH on enzyme activity 7 8 9 10 fast For most human enzymes, maximum activity occurs at about 98.6F (37C) rate of reaction slow 32 0 104 68 20 40 temperature 140 (F) 60 (C) Effect of temperature on enzyme activity