Presentation is loading. Please wait.

Presentation is loading. Please wait.

1.4 ENZYMES. Enzyme are _________________ catalysts.  Either tertiary or quaternary.  Names ususually end in ‘ase.’ CATALYST: substance that _____________.

Similar presentations

Presentation on theme: "1.4 ENZYMES. Enzyme are _________________ catalysts.  Either tertiary or quaternary.  Names ususually end in ‘ase.’ CATALYST: substance that _____________."— Presentation transcript:


2 Enzyme are _________________ catalysts.  Either tertiary or quaternary.  Names ususually end in ‘ase.’ CATALYST: substance that _____________ a chemical reaction without being consumed in the process.  Reactants  products. Enzyme can be used again. For chemical reaction to occur: bonds between reactant molecules break, rearrangement of atoms, new bonds form.  Reactants need to _______________ with enough _______________ and in the correct geometric ________________ for bond breaking to occur  transition state.

3 Activation Energies All reactions possess an activation energy, E A. Activation energy can be provided by:  Heat  Examples:  spark at a gas station.  Collision theory  Problem with heat as E A source? ___________________________________________. Catalysts allow reactions to proceed at suitable rates at moderate temperatures by reducing the a ACTIVATION ENERGY E A barrier.

4 Catalysts do not affect the free energy change, ∆G  Does not change endergonic  exergonic.  Only decreases the potential energy level of the transition state  more colliding reactants reach the transition state and become products. Does not affect the position of equilibrium  Forward and reversed reactions are catalyzed at the same rate  Rate at which equilibrium is reached is increased.

5 SUBSTRATES A substrate is the reactant that an enzyme acts on when it catalyzes a chemical reaction.  Substrate binds to particular site on enzyme to which it is attracted.  Very specific for substrate  will not even bind isomers.

6 MODEL OF ENZYME ACTIVITY Active site: region where substrate binds.  Usually a pocket or groove.  As substrate comes close to active sites, ____________________ of substrate interact with _________________ of _____________ on enzyme. Enzyme-substrate complex: substrate + enzyme Interactions between substrate and enzyme causes a ___________________ change of the enzyme.  Induced-fit model  enzyme ‘accomodates’ Substrates’ chemical bonds are stretched and bent  lowers the amount of energy needed to bring substrate to ‘transitional state.’ LOWERS THE ACTIVATION ENERGY!


8 Folded Paper & Paper Clip Analogy NOTE: ONE PAPER CLIP = ONE MONOMER TEAM 1: A) Make 3 polymers of 3 monomers each. No paper TEAM 2: A) Make 3 polymers of 3 monomers each. With paper WINNER: _________ How does the action of the paper enzyme relate to a real enzyme-catalyzed condensation reaction?

9 Factors Affecting the Rate of Enzyme Activity Temperature pH Concentration of substrate

10 Temperature Reactions increase in speed with an increase in temperature (collision theory). As temperature increases beyond a critical point, protein ______________ and loss of enzyme ____________ would occur. Every enzyme has an optimal temperature at which it works best.  Human enzymes: around _____.  Some thermophiles: _____.


12 pH Enzymes have pH at which they work best.  If environment is too acidic or basic, it may ___________________________ the enzyme. Pepsin  Catalyzes hydrolysis of proteins in the stomach  There is HCl in the stomach  pH = 2 Trypsin  Also hydrolyses proteins, but in the small intestine  Basic substance is secreted into small intestine  pH=8


14 Substrate Concentration As substrate concentration increases, more reactions can occur. However, as active sites become occupied, rate of reaction slows. A point called the ‘saturation’ (asymptote)is reached, in which all enzyme active sites are occupied. Reaction rate virtually constant: reaction can only occur when enzymes are vacant.

15 Cofactors and Coenzymes Cofactors: nonprotein components, such as dissolved ions, that are needed for some enzymes to function.  Zinc and manganese ions. Coenzymes: organic nonprotein cofactors that are needed for some enzymes to function.  Derivatives of many vitamins May bind to active site with covalent bonds, or weakly to the substrate

16 Enzyme Inhibition A variety of substances inhibit enzyme activity. Some are poisons, some are used by cell to control enzyme activity. Competitive Inhibitors  Similar to enzyme’s substrate  Bind to active site  Block normal substrate from binding  Reversible  Solution: increase concentration of enzyme’s substrate  compete. Noncompetitive Inhibitors  Do not compete with substrate  Bind to another part of the enzyme  conformation change  change in shape of active site  enzyme loses affinity for substrate.  DDT: poison that inhibits enzymes of the nervous system


18 Allosteric Regulation Cells control enzyme activity to coordinate cellular activities.  Restrict production of enzyme  Inhibiting the action of enzyme Allosteric Sites  Receptor sites  Substances bound to it may inhibit or stimulate enzyme’s activity.  Usually in proteins in quaternary structure with several subunits and several active sites. ALLOSTERIC REGULATORS:  Attach to allosteric sites using weak bonds. ACTIVATORS: stabilizes protein conformation to keep active sites available. ALLOSTERIC INHIBITOR: Stabilizes inactive form of enzyme  Noncompetitive inhibitors


20 FEEDBACK INHIBITION Method used by cells to control metabolic pathways involving a series of sequential reactions.  Each reaction catalyzed by a specific enzyme.  A product formed later in the sequence of reaction steps ALLOSTERICALLY INHIBITS an enzyme that catalyzes a reaction occurring earlier in the process.  Reduces the production of the inhibitor  a product of the process.  As product used up, less inhibition.  Enzyme in active form again, but cycle continues.  RESULT: AMOUNT OF PRODUCT KEPT TIGHTLY CONTROLLED BY FEEDBACK INHIBITION PROCESS.



23 METABOLIC PROCESSES are also controlled by controlling where certain enzymes are in the cell.  Some in mitochondria ______________________  Some are in chloroplasts _____________________  Some in the golgi bodies: _____________________  Some in lysosomes: __________________________ ETC.

24 Classwork/Homework Read pages 75-76 (Commercial and Industrial Uses of Enzyems) PPs 1-9

Download ppt "1.4 ENZYMES. Enzyme are _________________ catalysts.  Either tertiary or quaternary.  Names ususually end in ‘ase.’ CATALYST: substance that _____________."

Similar presentations

Ads by Google