First Law of Thermodynamics: Energy Can Neither Be Created or Destroyed Second Law of Thermodynamics: Every Energy Transfer Increases the Disorder (Entropy) of the Universe.
The Free Energy Change of a Reaction Tells Us Whether the Reaction Occurs Spontaneously ∆G = G Final State – G Initial State
The Relationship of Free Energy to Stability, Work Capacity, and Spontaneous Change
Energy Changes in Exergonic (energy releasing) and Endergonic (energy storing) Reactions
Disequilibrium and Work in Closed and Open Systems
Cells in our body experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium Figure 8.7 (b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equilibrium. ∆G < 0
ATP powers cellular work by coupling exergonic reactions to endergonic reactions A cell does three main kinds of work: –Mechanical –Transport –Chemical
The three types of cellular work are powered by the hydrolysis of ATP (c) Chemical work: ATP phosphorylates key reactants P Membrane protein Motor protein P i Protein moved (a) Mechanical work: ATP phosphorylates motor proteins ATP (b) Transport work: ATP phosphorylates transport proteins Solute PP i transportedSolute Glu NH 3 NH 2 P i + + Reactants: Glutamic acid and ammonia Product (glutamine) made ADP + P Figure 8.11
The Regeneration of ATP Catabolic pathways drive the regeneration of ATP from ADP and phosphate ATP synthesis from ADP + P i requires energy ATP ADP + P i Energy for cellular work (endergonic, energy- consuming processes) Energy from catabolism (exergonic, energy yielding processes) ATP hydrolysis to ADP + P i yields energy Figure 8.12
Example of an Enzyme-Catalyzed Reaction: Hydrolysis of Sucrose
Enzymes speed up metabolic reactions by lowering energy barriers
Enzymes 1.Proteins:enzymes proteins tertiaryquaternary structures. 1.Proteins:most enzymes are catalytic proteins, primarily tertiary and quaternary structures. 2.Catalysts:chemical agents accelerate 2.Catalysts:chemical agents that accelerate a reaction without being permanently changed in the process.
How Do Reactions Occur? Spontaneous reactions may occur very slowly. All reactions require free energy of activation (E A ) Uphill portion represents the E A required to start the reaction. Downhill portion represents the loss of free energy by the molecules in the reaction.
How can the E A barrier be overcome? Temperature Temperatures that are too high denature organic molecules, so what else is there? Enzymes lower the E A barrier so that reactions can occur at lower temperatures.
Enzymes Free Energy Progress of the reaction Reactants Products Free energy of activation Without Enzyme With Enzyme
Enzyme / Substrate Relationship: What is the substrate? It is the reactant upon which an enzyme reacts. Enzymes are substrate specific. Only the active site of the enzyme actually binds the substrate.
Substrate substance enzymeThe substance (reactant) an enzyme acts on. Enzyme Substrate
Active Site restricted region enzyme bindssubstrateA restricted region of an enzyme molecule which binds to the substrate. Enzyme Active Site Substrate
The Active Site Most enzyme-substrate interactions are the result of weak bonds. The active site may cause the enzyme to hold onto the substrate in a very specific way. The active site may provide a micro-environment (e.g. low pH) which enhances a reaction.
Induced Fit changeconfiguration enzyme’s active siteA change in the configuration of an enzyme’s active site (H and ionic bonds are involved). Inducedsubstrate.Induced by the substrate. Enzyme Active Site substrate induced fit
Cofactors and Coenzymes Inorganic substances (zinc, iron) vitamins enzymatic activityInorganic substances (zinc, iron) and vitamins (respectively) are sometimes needed for proper enzymatic activity. Example :Example : Iron quaternary structure-hemoglobin Iron must be present in the quaternary structure - hemoglobin in order for it to pick up oxygen.
Enzyme Inhibitors Two examples:Two examples: a.Competitive Inhibitors: resemble enzyme’s normal substrate competeactive site a.Competitive Inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Enzyme Competitive inhibitor Substrate
Enzyme Inhibitors b. Noncompetitive Inhibitors: do not enter the active sitebind to another part enzymeenzyme change its shape alters the active site Inhibitors that do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site. Substrate Enzyme active site altered Noncompetitive Inhibitor
Allosteric Regulation Regulatory molecules that bind to the enzyme’s allosteric site changing the shape of the enzyme. Allosterically regulated enzymes have a quaternary protein structure. Each subunit of the enzyme has an active site and an allosteric site. Allosteric activators stabilize the active site Allosteric inhibitors deactivate the active site.