Enzymes

• Enzymes are special proteins that helps breakdown chemicals
• Without catalyst, most cellular reactions would take place too slowly to support life.
• With the exception of some RNA molecules, all enzymes are globular proteins.
• Enzymes are extremely efficient catalysts, and some can increase reaction rates by 1020 times that of the uncatalyzed reactions.
• Enzymes are well suited to there roles in three major ways

  1. they have enormous catalytic power
  2. they are highly specific in the reactions they catalyze
  3. their activity as catalysts can be regulated
• Enzyme-catalyzed reaction accomplish many important organic reactions, such as ester hydrolysis, alcohol oxidation, amide formation, etc.
• Enzymes cause these organic reactions to proceed under mild pH and temperature conditions as well as accomplish in in just a seconds.
• Some of the earliest enzymes to be discovered were given names ending in "in" to indicate that they were proteins.
• Enzymes are usually derived by adding "-ase" to the name of the substrate or to a combination of substrate name and type of reaction.
• The specific portion of an enzyme (location) where the substrate binds while it undergoes a chemical reaction

  Active Site
• When the substrate binds to the enzyme active site an Enzyme-Substrate Complex is formed temporarily.
• Types of Reaction Catalyzed

  A) Oxidoreductase

  B) Transferases

  C) Hydrolases

  D) Lyases

  E) Isomerases

  F) Ligases

  
• "helper molecules"

  Enzyme Cofactors
• If the nonprotein component is tightly bound, and forms an integral part of the enzyme structure, it is a true prosthetic group.
• If the nonprotein component is weakly bound, and easily separated from the rest of the protein, it is called a cofactor.
• When the cofactor is an organic substance, it is a coenzyme. The cofactor may also be an inorganic ion (usually a metal cation).
• refers to the catalytic ability of an enzyme to increase the rate of a reaction

  Enzyme Activity
• number of molecules of substrate acted on by one molecule of the enzyme per minute

  Turnover number
• are experiments that are performed to measure enzyme activity

  Enzyme assays
• Enzymes differ widely in structure and specificity, but a general theory that accounts for their catalytic behavior is widely accepted.
• The enzyme and its substrates interact only over a small region of the surface of the enzyme, called the active site.
• • the active site is fixed, with a rigid shaped (lock)
  • the substrate (key) must fit exactly into the rigid enzyme (lock)

  Lock and Key Model of Enzyme Action
• The active site has a flexible shape that can change to accept a variety related substrate.

  Induced-Fit Model of Enzyme Action
• The mechanism of enzyme action

  A) Lock and Key Model

  B) Induced-Fit Model

  
• The four types of Enzyme Specificity

  1. Absolute Specificity- catalyzes one and only one substance
  2. Relative Specificity- catalyzes the reaction of structurally related substances
  3. Stereochemical Specificity- catalyzes the reaction of only one of two possible enantiomers
  4. Group Specificity- catalyzes a reaction on a function group of a variety of molecules.
• Factors Affecting Enzyme Activity

  1. Enzyme Concentration
  2. Substrate Concentration
  3. pH
  4. Temperature
• Factors affecting Enzyme Activity

  A) Temperature

  B) pH

  C) Concentration of Substrate

  D) Concentration of Enzyme

  
• An enzyme inhibitor is a substance that decreases the rate of an enzyme-catalyzed reaction.
• Irreversible Inhibition occurs when an inhibitor forms a covalent bond with a specific functional group of an enzyme, thereby inactivating it.
• is a rapidly-acting, highly toxic inhibitor, which interferes with the iron containing enzyme cytochrome oxidase

  Cyanide
• an antidote for cyanide, which converts it into thiocyanate, which does not bind to cytochrome

  Sodium Thiosulfate
• Heavy metal poisoning results when mercury or lead ions bind to -SH (thiol) groups on enzymes. It can also cause protein denaturation.
• Heavy-metal poisoning is treated by administering chelating agents
• are enzyme inhibitors that act on life processes that are essential to certain strains of bacteria

  Antibiotics
• binds reversibly to an enzyme, establishing an equilibrium between the bound and unbound inhibitor

  Reversible Inhibitor
• Two types of Reversible Inhibitor

  1. Competitive inhibitors bind to enzyme's active site and compete with the normal substrate molecules.
  2. Noncompetitive inhibitors bind reversibly to the enzyme at a site other than the active site, changing the 3D shape of the enzyme and the active site, so that the normal substrate no longer fits perfectly
• Enzyme Inhibitors

  A) Competitive

  B) Noncompetitive

  C) Irreversible

  
• To respond to changing conditions and cellular needs, enzyme activity requires very sensitive controls:

  1. Activation of Zymogens
  2. Allosteric Regulation
  3. Genetic Control
• are inactive precursors of an enzyme

  Zymogens or proenzymes
• Some enzymes in their active form would degrade the internal structures of the cell.