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An Introduction to Metabolism Metabolism = the totality of an organism’s chemical reactions. Manage the materials and energy resources of a cell Catabolic pathways = release energy by breaking down complex molecules into simpler compounds Ex: digestive enzymes break down food à release energyAnabolic pathways = consume energy to build complex molecules from simpler ones Ex: amino acids link to form muscle protein ENERGY = THE CAPACITY TO DO WORKKinetic energy (KE): energy associated with motionHeat (thermal energy) is KE associated with random movement of atoms or moleculesPotential energy (PE): stored energy as a result of its position or structure Chemical energy is PE available for release in an chemical reactionEnergy can be converted from one form to another Ex: chemical à mechanical à electrical Thermodynamics = the study of energy transformations that occur in nature-closed system – isolated from its surroundings. Ex: liquid in a thermos.-open system – energy and matter can be transferred between the system and its surroundings-organisms are open systems! First law of thermodynamics = the energy of the universe is constant Energy CAN be transferred and transformed Energy CANNOT be created or destroyed Also called the principle of Conservation of Energy Second law of thermodynamics = every energy transfer or transformation increases the entropy (disorder) of the universeDuring every energy transfer or transformation, some energy is unusable, often lost as heat Free energy: part of a system’s energy available to do work. delta G = change in free energyExergonic reaction: energy is released. Spontaneous reaction. delta G < 0Endergonic reaction: energy is required. Absorb free energy. Nonspontaneous. delta G > 0 A cell does 3 main kinds of work: mechanical, transport, chemical.Cells manage energy resources to do work by energy coupling: using an exergonic process to drive an endergonic one. ATP (adenosine triphosphate) is the cell’s main energy source in energy coupling.ATP = adenine +ribose + 3 phosphates-when the bonds break between the phosphate groups (by hydrolysis) à energy is released.-this release of energy comes from the chemical change to a state of lower free energy… not in the phosphate bonds themselves How ATP performs work:-exergonic release of Pi is used to do the endergonic work of the cell-when ATP is hydrolyzed, it becomes ADP (adenosine diphosphate) catalyst = substance that can change the rate of a reaction without being altered in the process. Enzyme = biological catalystSpeeds up metabolic reactions by lowering the activation energy (E needed to start reaction) Substrate specificity of enzymes;-the reactant that an enzyme acts on is called the enzyme’s substrate-the enzyme binds to its substrate, forming an enzyme-substrate complex-the active site is the region of the enzyme where the substrate binds-enzymes properly orient the reactant molecules-induced fit: enzyme fits snugly around substrate An enzyme’s activity can be affected by: temp, pH, chamicals Cofactors = nonprotein enzyme halpers such as mineralsCoenzymes = organic cofactors like vitamins Enzyme inhibitors:-competitive inhibitor: binds to the active site on an enzyme, competes with substrate-noncompetitive inhibitor: binds to another part of the enzyme à enzyme changes shape à active site is nonfunctional Regulation of enzyme activity:-to regulate metabolic pathways, the cell switches on/off the genes that encode specific enzymes-allosteric regulation: a protein’s function at one site is affected by binding of a regulatory molecule to a separate site (allosteric site) -activator: stabilizes active site -inhibitor: stabilizes inactive form-cooperativity: one substrate triggers shape change in other active sites à increase catalytic activity-feedback inhibition: end product of a metabolic pathway shuts down pathway by binding to the allosteric site of an enzyme. Prevents wasting chemical resources, increase efficiency of a cell
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