ENZYMES REACTIONS

OVER ARCHING CONCEPTS:

  1. Substances need a minimum amount of energy to react. 
  2. Enzymes lower the amount of minimum energy.
  3. Enzymes chemically recognize, bind, and alter specific reactants. They offer a stable microenvironment that is more favorable for reactions to occur compared to the surrounding environment! Salinity, pH, and temperature affect enzyme action.
  4. Most enzymes work in a multi-step metabolic sequence or pathway

Definitions:

  1. ACTIVATION ENERGY – minimum amount of collision energy that a reaction needs to get going
  2. SUBSTRATE – (reactants) part of the substrate is complementary in shape, size, solubility, and charge to the active site.
  3. ACTIVE SITES – pockets and crevices where substrates are bound and where specific reactions are catalyzed.
  4. TRANSITION STATE – the point at which the reaction can easily run to product or back to reactant.  A substrate is bound most tightly to an enzyme when it is in the transition state.
  5. BINDING ENERGY – the energy released from all weak interactions combined, that speeds a reaction rate.
  6. COFACTORS – substances that help catalyze most reactions.  They are metal ions or coenzymes (organic molecules with or without a vitamin component).  Because they give up and accept electrons easily they shift electron arrangements which help products form.
  7. ANTIOXIDANTS – help neutralize free radicals, the reactive, unbound fragments of reactions that have the wrong number of electrons.
  8. FREE RADICALS - Free radicals are chemically unstable atoms or molecules that cause other atoms and molecules in the body to become unstable as well, a process that causes extensive damage to cells and tissue, and could lead to a depressed immune system, infection, cardiovascular disease, joint disease, and mental decline. Free radicals are also thought to be a key component of the aging process.
  9. FEEDBACK INHIBITION – a change caused by an activity that shuts down that activity
  10. ALLOSTERIC ENZYMES - small regulatory enzymes that work by altering shape.  Allosteric enzymes work by “blocking” or “unblocking” specific binding sites so that a substrate is able or unable to react.

  MECHANISMS FOR INFLUENCING THE TRANSITION STATE:

a.       Helping substrates get together by binding at an active site, this boosts their local concentration by up to 10,000,000 times

b.       Orienting substrates in positions favoring reaction by putting reactive groups on a precise collision course

c.       Shutting out water which changes the microenvironment which lowers the activation energy significantly

d.       Inducing changes in enzyme shape allows for functional groups on the substrate’s surface to imprecisely fit the functional group in the active site.  By not fitting precisely the enzyme-substrate complex doesn’t become too stable and impede the reaction!