[Activation energy]: energy to start a reaction. Requires energy input to break bonds

Catalyst: substance that stresses chemical bonds & speeds up reaction in forward and/or reverse directions. Catalysts lower the activation energy needed for the reaction to occur. Enzymes are not changed or consumed by the reaction!

Enzymes: Special proteins that act as biological catalysts

1) Globular proteins with specialized 3-D shapes

2) Lower activation energy by

a) bringing two substrates together (greater chance to react)

b) stress bonds of a substrate (to break them)

Substrate: The reactant/s that the catalyst or enzyme binds with to in turn speed up the reaction.

Substrate specific: each enzyme catalyzes only one reaction (works on only 1-2 substrate/s)

[Active site]: surface shape or cleft on the enzyme to which the substrate must fit like a lock and key.

[A Second Model of how an Enzyme Works]

Induced fit: enzyme changes shape of active site so substrate fits perfectly. This allows some enzymes to catalyze several different reactions.

1. Proteases: Protein-digesting enzymes added to detergent to remove protein stains from clothes.

2. Pectinases: Enzyme that removes pectin from crushed fruit. Keeps juice from gelling, keeps it liquid for easier removal. Helps remove solids from juice.

Note: The scientific name of all enzymes ends in -ase.

[Factors affecting enzyme activity]

a) Temperature: Disrupts hydrogen bonds, alters protein shape (denature)

b) pH: hydrogen ion concentration disrupts bonds between amino acids

c). Substrate Concentration: Increased substrate concentration increases reaction rate until all enzymes are involved, then reactions level out

d) Enzyme Concentration: Increased enzyme concentration increases reaction rate until all substrate is used up, then reactions decrease.

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Biochemical Pathways

Several to many enzymes are placed side by side on membranes within cells, each enzyme completing one of the many steps to convert 1 substance into another. ("Assembly Line")

Amino Acids, Proteins, Dehydration Synthesis & Protein Shapes

Dehydration Synthesis & Hydrolysis (RM Chute) (See examples concerning proteins & carbos at bottom of that page too!)

Denaturation of a Protein (Cooking an Egg)

 

Factors Affecting Enzyme Activity

Enzymes (Prentice Hall) - Comprehensive review of enzymes. Click on Web Tutorial 6.2, then on Animation.

How Do Enzymes Work? (McGraw Hill)

Enzymes (Click all but the Allosteric Enzymes link!)

How Do Enzymes Work? (Starch Digestion)

How Temperature Affects Molecular Motion (BEC)

Enzyme Activity

Noncompetitive Enzyme Inhibition (Allosteric Enzymes)

Biochemical Pathways (Several different enzymes in close proximity that help change a substrate via several steps into its product)

 

[Enzyme inhibitors]: change shape of active site and shut off activity

a) [Competitive inhibitors]: Competitor molecule binds at active site, prevents substrate from binding.

b) [Non-competitive inhibitors]: End product binds at a allosteric (different site), changes shape of active site. Substrate can't bind.

c) Allosteric site: region where non-competitive inhibitor binds changing shape of enzyme.

Enzyme activators: bind to allosteric sites, keep enzyme in active state, increase activity of enzyme.