Metabolism: Energy and Enzymes

Energy Ability to do work, change matter Kinetic – energy in motion Potential – stored energy Chemical energy (food) Mechanical energy (motion)

Thermodynamics 2 Laws: 1. Law of conservation of energy – Energy cannot be created or destroyed, but it can be changed from one form to another (heat energy) 2. Energy cannot be changed from one form to another without a loss of usable energy. When heat is released, it is not longer available to do work, lost to the environment. Cells are 40% efficient, rest of energy is given off as heat

Entropy Used to indicate the relative amount of disorganization in universe Every process that occurs in cells increases the total entropy of the universe. More organized = less stable Clean room, more organized but less stable than a messy room entropy clip

Metabolic reactions Metabolism Reactants – products Free energy – amount of available energy to do work after a chemical reaction has taken place (G) Exergonic reactions – delta G is negative, products have less energy than the reactants, reaction is spontaneous, energy is released, ex. ATP breakdown Endergonic reactions – delta G is positive and products have more free energy than the reactants. Can only take place if there is an input of energy.

Adenosine Triphosphate Energy currency, universal, can be used in many different types of reactions. Composed of Adenine (nitrogen base), ribose sugar and 3 phosphate groups Uses of ATP Chemical work – synthesize macromolecules Transport work – pumps Mechanical work – muscle contraction, cilia to beat, chromosomes to move.

Coupling reactions Energy released by exergonic reactions drive endergonic reactions. ATP breakdown is exergonic

Function of ATP Chemical work – helps to synthesize macromolecules Transport work – supplies energy for pumps across membrane Mechanical work – supplies energy to do work, muscle contraction, cilia beat…

Chemical reactions Reactants  products Absorb or release energy Bonds broken and new ones formed CO2 + H2O + light  C6H12O6 + O2 Absorb or release energy Water freezing – energy released Ice melting – energy absorbed metabolism

Enzyme activity Activation energy is used to start chemical reactions Biochemical reactions – reactions in cells Enzyme – increase speed of chemical rxn Catalyst – reduce activation energy of chem. Rxn Homeostasis Most are proteins End in -ase Different enzymes catalyze different chemical reactions ex. Lactase/lactose

Degradative reactions – substrate broken down Synthesis reaction – substrates combine, larger product Enzymes are not used up in the reaction, available to bind to another substrate. Active site – area on enzyme that the substrate binds to. Induced fit model- enzyme complex undergoes a slight change in shape

Enzyme substrate complex

Factors that affect enzyme activity Temperature pH Can change shape of enzyme – denaturing If enzyme changes, chemical reaction can not take place Cofactors – non protein helpers Inorganic - Zinc, iron, copper Organic – called a coenzyme, vitamins

Enzyme inhibitors Competitive inhibitors – mimic substrates and compete for active site, reduce productivity Noncompetitive inhibitors – do not bind to active site, but the allosteric site When bound, changes shape of active site Toxins and poisons