Lecture 4 Enzymes
Jan 05, 2016
Lecture 4
Enzymes
Enzymes
• Proteins
• Catalyze all cellular reactions
• Enzymes are not changed by the reactions, and can be reused
Protein Shape
• Proteins need the proper shape to function
• Increased temperature, high or low pH, or certain solvents, cause the bonds within the protein to be broken
• Denatured protein: no longer functions
Enzymes
• Function by lowering the activation energy of a chemical reaction so it is more likely to occur
• Enzymes weaken chemical bonds in the substrate
Enzymes
• Very specific due to 3-D shape• Contain an active site: region where a
specific substrate binds• Substrate: substance upon which an
enzyme acts• Enzyme + Substrate Enzyme-Substrate
complex
Enzyme + Product
Cofactors and Coenzymes
• Some enzymes need help to build
active site
• Cofactors: inorganic molecules that help build active site of enzyme
• Coenzymes: organic molecules that help build the active site
Figure 5.3
Enzymes
• Often Team Up in Metabolic Pathways– A metabolic
pathway is a sequence of chemical reactions
Factors Influencing Enzymatic Activity
• Temperature: chemical reaction increases as temperature increases, up to a certain point
• pH: most enzymes has optimum pH
• Substrate concentration: Increase substrate amount, increases reaction rate
• Inhibition
Figure 5.5 - Overview
Enzyme Inhibition
• Competitive Inhibition: inhibitor competes with the substrate for the active site
• Non-Competitive inhibition: when inhibitor and substrate act at different sites on the enzyme
• Feedback Inhibition: inhibits an enzyme in the pathway so no product is available to feed the next reaction
Figure 5.7 - Overview
Figure 5.8
Classification of Enzymes
Classification- Based on where enzyme activity occurs
• Exoenzymes
• Endoenzymes