1. What is an enzyme?
General overview:
• A biological catalyst
• Increases the rate of a reaction
• Is not itself consumed in the reaction
• Lowers the activation energy of a reaction
• Reactions will not occur at a rate that supports
survival unless enzymes are present
2. Enzymes Are Biological
Catalysts
• Enzymes are proteins that carry out most
catalysis in living organisms.
– Unique three-dimensional shape enables an
enzyme to react with specific substrates.
– Because the enzyme itself is not changed or
consumed in the reaction, only a small amount
is needed, and can then be reused.
3. Free Energy
• Free energy refers to the amount of energy
actually available to break and subsequently form
other chemical bonds.
– in a cell - amt of energy contained in a molecules
chemical bonds
• Energy involved in chemical reactions:
• endergonic - any reaction that requires an input
of energy
• exergonic - any reaction that releases free
energy
4. Activation Energy
• Activation energy refers to the extra energy
required to destabilize existing chemical bonds
and initiate a chemical reaction.
• catalyst - substance that lowers the
activation energy
• cannot violate laws of thermodynamics
– Remember those from physical science??!!?!
6. How do enzymes work?
• An enzyme reacts only with specific
substrates (Another word for reactants)
– Active site- the part of an enzyme that actually
interacts with the reactants
7. Enzymes
• Most enzymes are globular proteins with
one or more active sites.
– Substrates bind to the enzyme at these active
sites, forming an enzyme-substrate complex.
9. Control of enzyme activity:
• Temperature and pH of solution
• Concentration of enzyme and substrate molecules
• Presence of substances that stimulate or
inhibit reactions
• Availability of cofactors (or coenzymes)
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14. Inhibitors and activators
• inhibitor - substance that binds to an enzyme and
decreases its activity
• competitive inhibitors - compete with the substrate for the
same active site
• noncompetitive inhibitors - bind to the enzyme in a
location other than the active site
– allosteric sites - specific binding sites acting as on/off switches
– Ex: sites of cofactors
