Metabolism
Enzymes: review
Anabolism vs Catabolism
What is necessary for a
chemical reaction to begin?
• Reactant(s) must come together in the right orientation
• With enough energy
• So ho do enzymes catalyze this process?
• Lowers activation energy
• Template for proper orientation of substrates
• As active site “holds” substrate – can stress/strain the substrate,
breaking bonds
• More conducive microenvrionments – ie altering pH
Enzyme specificity
• What contributes to it?
Complementary fit
Lock and Key Model
Induced Fit Model (replaces lock and key)
• Enzymes = globular proteins
• Shape shifters – subtle
• Active site is not rigid
• Can fit more snugly around substrate
Catalysis
Saturation – limiting factor = max
enzymatic rate
Enzyme efficiency
• Determined by environmental factors
• Optimal conditions
Cofactors
• Nonprotein helpers
• Zinc, iron, copper
• Vary in how they bind to enzyme
• Perform a critical function in catalysis
coenzymes
• Organic cofactors
• Most vitamins
Other factors influencing reaction rate…
• inhibitors
• Reversibility
Competitive inhibition
Noncompetitive inhibition
examples
• Sarin: nerve gas
• DDT and parathion
• antibiotics
Regulation
• Selective inhibition
• Cells control when and where enzymes are active
• control the building of the protein
• Control the protein once its built
Allosteric regulation
• Protein function at one site is affected by the binding of a regulatory
molecule to a separate site
• Can inhibit or stimulate