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Biochemical Reactions. The Active Cell. Biological Reactions. Metabolism is a term used to refer to all the chemical reactions that take place in a living organism Two main categories of metabolic reactions Catabolic reactions are those that break large molecules into small ones E.g.
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Biochemical Reactions The Active Cell
Biological Reactions • Metabolism is a term used to refer to all the chemical reactions that take place in a living organism • Two main categories of metabolic reactions • Catabolic reactions are those that break large molecules into small ones • E.g. • digestion of proteins • respiration • Anabolic reactions are those that build larger molecules • E.g. photosynthesis
Gibbs Free Energy and Metabolism • Gibbs free energy measures the likelihood that a reaction will proceed spontaneously • A calculation based on the energy required to break the bonds between the atoms of the reactants as compared to the products
Catabolic reactions • Most catabolic reactions release energy • This energy is available to do work (physical definition of work) • These types of reactions are called exothermic in chemistry – energy is released at once in the form of heat • Ea = activation energy • ΔG = Gibbs Free Energy
Catabolic Reactions • In biological system, a sudden release of heat energy in the living cell will cause it to die • Therefore, energy is released in a controlled manner through a variety of chemical intermediates • Thus, in biology, we call these exergonic reactions
Anabolic Reactions • These are chemical reactions that result in larger molecules • Usually require a large energy input • In chemistry, these are called endothermic reactions – energy input in the form of heat
Anabolic Reactions • As with catabolic reactions, these process are highly controlled in the living cell • Cannot add energy directly by heating the reactants • Must do so in small controlled amounts • These types of reactions are called endergonic
Enzymes • Enzymes are functional proteins in that they are the main chemical drivers of life • These are protein molecules that accelerate and control biochemical reactions by reducing the activation energy of a reaction • The organic equivalent of a catalyst
Catalysis • Refers to the process by which a chemical reaction proceeds with the assistance of a helper compound or molecule • The helper is not consumed in the reaction • General form is: Reactants + Catalyst Reactants/Catalyst complex Products + Catalyst
Enzymes • Similar pathway for reactivity • Reactants are called substrates Substrates + Enzyme Activated Enzyme Substrate complex Products + Enzyme
Enzymes • As with catalysts, enzymes reduce the amount of activation energy needed to start a reaction. • The energy curve of an enzyme mediated reaction will have a lower activation energy than that without the enzyme
Enzymes • Note that ΔG for an enzyme mediated reaction does not change • Only the activation energy is changed – reduced by a factor • Enzymes work in one of two ways • Catabolic enzymes have an active site that will place stress on a specific bond causing it to break • Anabolic enzymes have an active site that will bring two molecules together in a configuration that permits bonding
Controlling Enzyme Activity • Enzymes are reusable • Active enzymes will continue to function as long as substrate is available to react • Often, it is essential to control when an enzyme is active and when it is not • Such controls are important in controlling how and when biochemical reactions take place
Controlling Enzyme Activity • Several methods by which enzyme action is controlled • Co-Enzymes and Co-Factors • These are molecules or minerals that are essential for the enzyme to function properly • Inhibitors • These are molecules that interfere with the functioning of the enzyme • Two types • Competitive inhibitors • Allosteric inhibitors • Biochemical Pathways
