Metabolism: Energy and Enzymes Chapter 6

Energy = the ability to do work Kinetic Energy (energy of motion) Potential Energy (stored energy) First Law of Thermodynamics - the law of conservation of energy Second Law of Thermodynamics - energy cannot be changed without a loss of usable energy (heat)

Metabolic Reactions Reactants  Products Exergonic (exothermic) = releases energy (-ΔG) Endergonic (endothermic) = absorbs energy (+ΔG) Where +ΔG meets –ΔG the point of chemical equilibrium is reached.

What is The Gibbs free energy, originally called available energy, was developed in the 1870s by the American mathematician Josiah Willard Gibbs. In 1873, Gibbs described this “available energy” as the greatest amount of mechanical work which can be obtained from a given quantity of a certain substance in a given initial state, without increasing its total volume or allowing heat to pass to or from external bodies, except such as at the close of the processes are left in their initial condition. [3]Josiah Willard Gibbsvolumeheat [3]

ATP - the energy currency of cells (adenosine triphosphate) Functions: 1. CHEMICAL WORK - Supplies energy needed to make macromolecules that make up the cell (and organism) 2. TRANSPORT WORK - Supplies energy needed to pump substances across the cell membrane 3. MECHANICAL WORK - supplies energy needed to make muscles contract and other cellular parts to move (flagella) +ΔG+ΔG

Reaction Rate The Rate is independent of G The Rate is dependent by the amount of activation energy required  catalysts added

Enzyme Quiz

Metabolic Pathways & Enzymes Enzyme - protein molecule that functions as an organic catalyst to speed reactions Substrate - reactants in the enzymatic reaction, this is what an enzyme attaches to Energy of Activation - the energy required to cause the reaction

Properties of Enzymes: Enzymes are made of proteins. They speed up chemical reactions inside the cytoplasm. They are needed only in small amounts They remain unchanged after each reaction and can therefore be reused Each enzyme is specific for a substrate

Induced Fit Model - substrates and enzymes fit together like a lock and key. (Degradation vs Synthesis) breaking down vs building

Factors Affecting Enzymatic Speed 1. Substrate concentration 2. Temperature & pH * 3. Enzyme concentration Enzymes can be denatured - they change shape so much that they are no longer effective. High temp or pH can cause denaturation.

Siamese cats have an enzyme that works at lower temperatures only, causing the nose and ears to become a darker color than the rest of the body.

Enzymatic Inhibition - when a substance binds to an enzyme and decreases its activity. (Usually reversible) Competitive Inhibition  active site compromised Noncompetitive Inhibition  active site not compromised; allosteric site **Both are forms of feedback inhibition

Some inhibitors are NOT reversible - poisons like cyanide, lead poisoning all affect enzymes QUESTION: What type of inhibition is pictured below?

Some enzymes require… CoFactors: “helper molecules” –CoEnzymes (an additional protein that has to be present) –Prosthetic Groups (an additional protein that has to be attached to the enzyme) …in order to run a chemical reaction.