An Organism’s Metabolism Transforms Matter and Energy, Subject to the Laws of Thermodynamics

Potential and Kinetic Energy: Cheetah at Rest and Running Energy is lost as heat

Potential and Kinetic Energy:

 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

A cell does three main kinds of work: Mechanical Transport Chemical 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 transported Glu NH3 NH2 + Reactants: Glutamic acid and ammonia Product (glutamine) made ADP Figure 8.11

The Structure and Hydrolysis of ATP

Energy COUPLING by Phosphate Transfer

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

An active cell needs millions of molecules of ATP per second to drive its biochemical machinery. They’re consumed in less than a second and an average person produces and hydrolyzes about 40 kg of ATP per day!

Enzymes speed up metabolic reactions by lowering energy barriers

Enzymes 1.Proteins: most enzymes are catalytic proteins, primarily tertiary and quaternary structures. 2.Catalysts:chemical agents that accelerate a reaction without being permanently changed in the process.

Example of an Enzyme-Catalyzed Reaction: Hydrolysis of Sucrose

How Do Reactions Occur? Spontaneous reactions may occur very slowly. All reactions require free energy of activation (EA) Uphill portion represents the EA required to start the reaction. Downhill portion represents the loss of free energy by the molecules in the reaction.

Is this reaction exergonic or endergonic?

How can the EA barrier be overcome? Temperature Temperatures that are too high denature organic molecules, so what else is there? Enzymes lower the EA barrier so that reactions can occur at lower temperatures.

Enzymes Without Enzyme With Enzyme Free Energy Progress of the reaction Reactants Products Free energy of activation

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 The substance (reactant) an enzyme acts on. Enzyme Substrate

Active Site A restricted region of an enzyme molecule which binds to the substrate. Enzyme Substrate Active Site

Enzyme Animations http://www.biologyalive.com/life/classes/apbiology/documents/Unit%203/media5/micro_enzyme-substrate.swf http://www.wiley.com/college/test/0471787159/biology_basics/animations/howEnzymesWork.html http://www.cengage.com/biology/discipline_content/animations/enzyme_role_m.html http://bcs.whfreeman.com/webpub/Ektron/pol1e/Animated%20Tutorials/at0302/at_0302_enzyme_catalysis.html

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 A change in the configuration of an enzyme’s active site (H and ionic bonds are involved). Induced by the substrate. Enzyme Active Site substrate induced fit

Enzymatic Reaction substrate (sucrose) + enzyme (sucrase)  enzyme-substrate complex  and + sucrase glucose fructose products + enzyme

Enzyme Activity is Affected by: Temperature pH Enzyme Concentration Substrate Concentration

Cofactors and Coenzymes Inorganic substances (zinc, iron) and vitamins (respectively) are sometimes needed for proper enzymatic activity. Example: Iron must be present in the quaternary structure - hemoglobin in order for it to pick up oxygen.

Enzyme Inhibitors Two examples: a. Competitive Inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Substrate Enzyme Competitive inhibitor

Enzyme Inhibitors b. Noncompetitive Inhibitors: 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 Noncompetitive Inhibitor active site altered

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.

Feedback Inhibition A metabolic pathway is switched off by the inhibitory binding of its end product to an enzyme earlier in the pathway

In the amylase lab, the amylase broke down the polysac- charides (starches) into _______. 2) Enzymes work by lowering the ___________ _________ required for a reaction to occur.