Pineapple contains a chemical called bromelain that contains two proteases. Bromelin is used in many meat tenderizers for this purpose (and that's why cooking ham with pineapple makes it tender). Jell-O packages warn you not to put pineapple chunks into the gelatin. Jello is a protein mesh of collogen with trapped pockets of liquid; the bromelin cuts the protein chains and keeps the gelatin from jelling properly. In the canning process the pineapple is heated, denaturing the pineapple – thus not ruining the desert.

What Factors Determine the Spontaneity of a Reaction? Entropy Entropy Enthalpy Enthalpy What ties the two together is: What ties the two together is: Gibbs Free Energy Gibbs Free Energy (Available energy)

Entropy Symbol S Symbol S A measure of molecular randomness or disorder. A measure of molecular randomness or disorder.

Disorder Chemical processes spontaneously go to a direction of increased entropy. Chemical processes spontaneously go to a direction of increased entropy. Why? Why? Probability Probability

Probability of Disorder Is there a higher probability your room will be messy or neat as time goes on? Is there a higher probability your room will be messy or neat as time goes on?

Example: Which has more entropy in its system? Which has more entropy in its system? H 2 O (s) orH 2 O (g) H 2 O (s) orH 2 O (g)

Enthalpy (Heat of Reaction) Definition: Enthalpy is a thermodynamic property of a system. It reflects the capacity to do non-mechanical work and the capacity to release heat. Enthalpy is denoted as H.

So…… When When  H 0  H 0 (exothermic) (Greater Disorder) the reaction would be spontaneous. NOTE: exothermic describes a process or reaction that releases energy from the system.

What about exothermic and less disorder? Use Gibbs Free Energy Gibbs Free Energy can be used to predict the spontaneity and it ties together the  H and the  S, the two driving forces of reactions (T = temperature). Gibbs Free Energy can be used to predict the spontaneity and it ties together the  H and the  S, the two driving forces of reactions (T = temperature).  G=  H-T  S  (all quantities refer to the system)

Gibbs Free Energy  Energy that can be converted to work.   G<0 for spontaneous processes.   G=0 at equilibrium.

Enzymes Some basic information.. Enzymes are protein catalysts, which are not consumed in rxns (catalysts speed up reactions and lower E A ) Enzymes are protein catalysts, which are not consumed in rxns (catalysts speed up reactions and lower E A ) Reconfigure broken bonds to create products Reconfigure broken bonds to create products Non-biological rxns use heat as catalyst Non-biological rxns use heat as catalyst Since proteins denature in high heat, enzymes are needed instead Since proteins denature in high heat, enzymes are needed instead Each enzyme has an optimal temp. and pH Each enzyme has an optimal temp. and pH Enzymes do not affect ΔG or equilibrium point Enzymes do not affect ΔG or equilibrium point Enzymes attach to substrates (reactants) in specific configurations Enzymes attach to substrates (reactants) in specific configurations So… enzymes decrease the potential energy of transition state molecules, thus allowing a greater proportion of colliding reactants to reach transition state and become products.

Reaction Progress Graphs Exergonic: producing energy and therefore occurring spontaneously Endergonic - requiring energy to proceed ExergonicEndergonic

Enzymes Since proteins denature in high heat, enzymes are needed instead Since proteins denature in high heat, enzymes are needed instead Each enzyme has an optimal temp. and pH Each enzyme has an optimal temp. and pH

Example

1.Substrate binds to grooved active site, where isomers are not recognized 2.Functional groups interact which changes the shape of enzyme to an induced (and better) fit 1.Now called enzyme-substrate complex Induced Fit Model

3.Enzyme now stretches and bends bonds that would normally break, but bending lowers the E A 4.Once bond breaks, enzymes conformation changes and it loses its affinity for the products 5.Products are released

HOW ?? The active site may: Stretch or bend bonds making them easier to break Bring two substances together in the correct position for a reaction to occur Transfer electrons to or from the substrate destabilizing it Add or remove hydrogen ions to or from the substrate (act like an acid or base)

Controlling Enzymes: Enzyme Inhibition 1. Competitive Inhibition Substance called inhibitor competes with the substrate for the enzyme’s active site (looks like substrate) Substance called inhibitor competes with the substrate for the enzyme’s active site (looks like substrate) Enzyme cannot perform Enzyme cannot perform Inhibition is reversible if the substrate’s concentration is increased over the competitor’s Inhibition is reversible if the substrate’s concentration is increased over the competitor’s

2.Non-competitive Inhibition Inhibitor attaches to a different spot on enzyme This changes enzymes shape – loses affinity for substrate

Competitive and Non- competitive Inhibition

Controlling Enzymes: Allosteric Regulation Cells can further control enzyme activity by: 1. Restricting the production of the enzyme 2. Inhibiting the action of the enzyme Some enzymes have allosteric sites that, when a substance enters and weakly bonds, can inhibit (inhibitor) or stimulate (activator). Note: Allosteric inhibitors are non-competitive inhibitors Note: One allosteric regulator can affect ALL active sites.

Allosteric Regulation

Controlling Enzymes: Feedback Inhibition Method of control where a product formed later in a chain of rxns returns to the beginning to allosterically inhibit an earlier enzyme Method of control where a product formed later in a chain of rxns returns to the beginning to allosterically inhibit an earlier enzyme The affect is reduced production of the inhibitor (final product) The affect is reduced production of the inhibitor (final product) Eventually, all inhibitor product disappears, terminating inhibition and rxns begin again as enzyme takes active form Eventually, all inhibitor product disappears, terminating inhibition and rxns begin again as enzyme takes active form Overall effect: amount of product is tightly controlled Overall effect: amount of product is tightly controlled

Feedback Inhibition Homework: Read and make notes on pages 75-6: Commercial and Industrial Uses of Enzymes

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