Enzymes and Catalysts

Catalyst: A chemical agent that accelerates a chemical reaction without being permanently changed in the process

Enzyme: A protein molecule that acts as a Biological Catalyst

Substrate: the molecule that the enzyme binds to; the molecule that undergoes the reaction

5 Things all enzymes have in common:

1.  They don’t make anything happen that could not happen on its own

2.  They are NOT permanently altered or used up by a reaction (they are re-used)

3.  The same enzyme usually works for the forward and reverse directions of a reaction

4.  All enzymes work on specific substrates

5.  Enzymes function to lower the Activation Energy of a chemical reaction

Activation Energy: The extra energy required to destabilize existing chemical bonds and initiate a chemical reaction

Enzymes increase the rate of reactions by lowering the Activation Energy!

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Active Site: “Pocket” on the enzyme in which the substrate binds to forming an Enzyme-Substrate Complex (lock and key)

Products: what the substrate is turned into after binding to the enzyme; gets released

Factors that affect Enzyme Activity:

1.  Temperature: rate increases with temp. increase only until the temperature optimum is reached; maximizes random molecular movement

·  Optimal temp range for most human enzymes = 35-40° C (94-99° F )

2.  pH: pH optimum = pH 4 to 6; pepsin (a digestive enzyme) works best at pH 2

3.  Ionic Concentration: high ion concentrations (salt) slow down enzyme activity

4.  Cofactors & Coenzymes: presence of small non-protein molecules required for proper enzyme catalysis

·  Cofactors = inorganic (Zn, Cu, metals)

·  Coenzymes = organic (vitamins)

5.  Enzyme Inhibitors: substance that binds to an enzyme and decreases its activity

·  Competitive Inhibition = resemble an enzymes normal substrate, compete with it for the active site, block it

·  Noncompetitive Inhibition = binds to another part of the enzyme besides the active site; causes the enzyme to change shape so the active site can’t bind to the substrate

6.  Allosteric Regulation: receptor site on some part of the enzyme other than the active site; serve as a chemical “on/off” switch (activator/inhibitor)

7. Feedback Inhibition: the product of one metabolic pathway can become the inhibitor for another

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