Enzymes

Question: enzymesWhat are enzymes?

Enzymes Answer: 1.Proteins:enzymesproteins tertiaryquaternary structures. 1.Proteins:most enzymes are proteins, primarily tertiary and quaternary structures. 2.Catalyst:chemical agentaccelerates 2.Catalyst:chemical agent that accelerates a reaction without being permanently changed in the process.

Enzymes 3.Selective: catalyze(Specificity - depends upon 3D shape). 3.Selective:enzymes are specific for which they will catalyze (Specificity - depends upon 3D shape). 4.Recycled: 4.Recycled: enzymes are reusable. 5.“ase”examples:sucrase 5.“ase” endings:examples:sucrasemaltaselactase

Question: enzymesHow do enzymes work?

Enzymes Answer: Enzymes lowering the free energy of activationEnzymes speed up the cell’s chemical reactions by lowering the free energy of activation.

Enzymes Free Energy Progress of the reaction Reactants Products Free energy of activation Without Enzyme With Enzyme

Substrate substanceenzymeThe substance (reactant) an enzyme acts on. Enzyme Substrate

Active Site restricted region enzyme bindssubstrateA restricted region of an enzyme molecule which binds to the substrate. Enzyme Active Site Substrate

Induced Fit changeconfigurationenzyme’s active siteA change in the configuration of an enzyme’s active site (H and ionic bonds are involved). Inducedsubstrate.Induced by the substrate. Enzyme Active Site substrate induced fit

Enzymatic Reaction substrate (sucrose)enzyme (sucrase)  substrate (sucrose) + enzyme (sucrase)  enzyme-substrate complex  and+ sucrase glucosefructose glucose fructose products +enzyme

E + S  ES  E + P

What Affects Enzyme Activity? Three factors:Three factors: 1.Environmental Conditions 2.Cofactors and Coenzymes 3.Enzyme Inhibitors

1. Environmental Conditions Enzymatic reactions environmental conditionsEnzymatic reactions are very specific. The following environmental conditions affect enzymatic reactions: (Non-specific Inhibitors) 1.Temperature (extremes most dangerous): - high temps denature enzyme. - high temps may denature the enzyme. 2.pH (most like pH - neutral) acid/base 3.Ionic concentration (salt ions) 4.Alcohol (disinfectants) 5.Heavy Metals (Silver nitrate) 6. Reducing agents (Break S-S bonds)

2. Cofactors and Coenzymes Cofactors-Inorganic substances (zinc, iron)Cofactors-Inorganic substances (zinc, iron) also called minerals. Coenzymes- organic substances not proteins also called Vitamins enzymatic activityBoth are sometimes needed for proper enzymatic activity. Example:Example: Ironquaternary structure-hemoglobin Iron must be present in the quaternary structure - hemoglobin in order for it to pick up oxygen.

3. Enzyme Inhibitors Two examples:Two examples: a.Competitive inhibitors: resembleenzyme’s normal substrate competeactive site a.Competitive inhibitors: are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site. Enzyme Competitive inhibitor Substrate

3. Enzyme Inhibitors b.Noncompetitive inhibitors: do not enter the active site bind to another part enzyme enzymechange its shape alters the active site Inhibitors that do not enter the active site, but bind to another part of the enzyme causing the enzyme to change its shape, which in turn alters the active site. Substrate Enzyme active site altered Noncompetitive Inhibitor

Non-competitive cont. Non-competitive inhibition is irreversible They can bond at, near, or remote from the active site –Also called Allosteric Regulation (inhibitor binds away from active site) –Means “other site” –Nerve gases

Naming of Enzymes –mostly historical : substrate + "ase" Remember Chitinase, Amylase, Cellulase? Sucrase breaks sucrose into glucose and fructose Also based on type of reaction

Common Enzymes Transferases catalyze the transfer of functional groups Hydrolyases catalyze hydrolysis - adds water across C-C bonds Lyases add or remove functional groups to form C=C bonds Isomerases catalyze isomerizations - change from one isomer to another Ligases condensation of 2 substrates