Enzymes A protein catalyst Enzymes are important proteins found in living things. An enzyme is a protein that changes the rate of a chemical reaction. They speed metabolic reactions.

Nothing works without enzymes! How important are enzymes? – all chemical reactions in living organisms require enzymes to work building molecules – synthesis enzymes breaking down molecules – digestive enzymes – enzymes speed up reactions “catalysts” ++ enzyme We can ’ t live without enzymes!

Examples  synthesis  digestion ++ enzyme

Enzymes are proteins Each enzyme is the specific helper to a specific reaction – each enzyme needs to be the right shape for the job – enzymes are named for the reaction they help sucrase breaks down sucrose proteases breakdown proteins lipases breakdown lipids DNA polymerase builds DNA Oh, I get it! They end in -ase

Enzymes aren’t used up Enzymes are not changed by the reaction – used only temporarily – re-used again for the same reaction with other molecules – very little enzyme needed to help in many reactions enzyme substrateproduct active site

It’s shape that matters! Lock & Key model – shape of protein allows enzyme & substrate to fit – specific enzyme for each specific reaction

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Enzyme vocabulary Enzyme – helper protein molecule Substrate – molecule that enzymes work on Products – what the enzyme helps produce from the reaction Active site – part of enzyme that substrate molecule fits into

The cellular environment affects enzyme activity Enzyme activity is influenced by – temperature Denaturation: process – salt concentration in which protein unravels – pH losing its shape & hence Some enzymes require function nonprotein cofactors ( usually minerals) – Some cofactors are organic molecules called coenzymes ( usually vitamins)

What affects enzyme action Correct protein structure – correct order of amino acids – why? enzyme has to be right shape Temperature – why? enzyme has to be right shape pH (acids & bases) – why? enzyme has to be right shape

Order of amino acids Wrong order = wrong shape = can’t do its job! DNA chain of amino acids folded protein right shape! wrong shape!

Temperature Effect on rates of enzyme activity – Optimum temperature greatest number of collisions between enzyme & substrate human enzymes – 35°- 40°C (body temp = 37°C) – Raise temperature (boiling) denature protein = unfold = lose shape – Lower temperature T° molecules move slower fewer collisions between enzyme & substrate

37° Temperature temperature reaction rate What’s happening here?! human enzymes

How do cold-blooded creatures do it?

pH Effect on rates of enzyme activity – changes in pH changes protein shape – most human enzymes = pH 6-8 depends on where in body pepsin (stomach) = pH 3 trypsin (small intestines) = pH 8

7 pH reaction rate stomach pepsin intestines trypsin What’s happening here?!

For enzymes… What matters? SHAPE!

Enzyme inhibitors block enzyme action Inhibitors interfere with enzymes – A competitive inhibitor takes the place of a substrate in the active site – A noncompetitive inhibitor alters an enzyme’s function by changing its shape Competitive inhibitor Noncompetitive inhibitor ENZYME INHIBITION NORMAL BINDING OF SUBSTRATE Substrate Active site Enzyme

5.16 Enzyme inhibitors block enzyme action and can regulate enzyme activity in a cell Enzyme inhibitors are important in regulating cell metabolism –Often the product of a metabolic pathway can serve as an inhibitor of one enzyme in the pathway, a mechanism called feedback inhibition –The more product formed, the greater the inhibition, and in this way, regulation of the pathway is accomplished Copyright © 2009 Pearson Education, Inc.

Connection: Some pesticides and antibiotics inhibit enzymes Certain pesticides are toxic to insects because they inhibit key enzymes in the nervous system Many antibiotics inhibit enzymes that are essential to the survival of disease-causing bacteria – Penicillin inhibits an enzyme that bacteria use in making cell walls