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