Lesson 13 – Enzyme Activity

Learning Goals Learn how enzyme activity can be affected by: environmental conditions regulation by the cell Observe/inquire about enzyme activity using a PEOE.

Enzyme Function Summary Catalyze reactions in living organisms lower Ea function in anabolic and catabolic pathways Induced fit model 3D shape (conformation) a result of their amino acid sequence.

Optimal Environments If an enzyme’s function is dependent on its folding and shape, and we know certain variables can affect the shape of the enzyme…… Well, what could we possibly conclude?

Temperature Affects Activity At first, increasing temperature will increase enzyme activity, as more kinetic energy is provided to molecules (more collisions). After reaching an optimum, increases in temperature begin to denature the enzyme, breaking its secondary, tertiary and quaternary structure Eventually, complete loss of function will occur when all enzyme molecules are denatured. The activity curve for a human enzyme shows optimal function at 37oC, but some enzymes in certain archaebacteria function at temperatures even above 100oC!

pH Affects Activity Folding (and thus activity) is also affected by pH, as hydrogen ion concentration will affect amino acid interactions. Pepsin works best at pH 2 where does it function? Trypsin works best at pH 8

Other Ways to Affect Rate A limiting factor is the factor that is preventing the reaction from occurring at a faster rate - for example, the substrate, or the enzyme concentration could be limiting. If we increase the concentration of the limiting factor (eg. substrate concentration), we will increase the rate of reaction up to when that factor is no longer limiting (enzyme concentration is now limiting).

Cofactors/Coenzymes Some enzymes require non-protein cofactors for proper biological function. Some cofactors are inorganic, such as metal ions like Zn2+, Mg2+, Cu+, or Fe2+ Some cofactors are organic, and are called coenzymes - we will see some good examples of these in the next unit. Many coenzymes are synthesized from the vitamins we get in our diet.

Enzyme Inhibition A variety of molecules can inhibit enzyme activity by interfering with substrate binding or the shape of the enzyme itself. Competitive inhibitors bind directly to the active site and prevent substrate binding (often these are structurally similar to the substrate). Some poisons work this way (eg. cyanide). Non-competitive inhibitors bind to different sites (allosteric sites) and affect the shape of the active site.

Enzyme Activation Other molecules can be activators of enzyme activity, in effect doing the opposite of what an inhibitor does.

Regulation Cells can actually control the activity rate of their enzymes in two primary ways: Regulating production of enzyme itself (too little reaction, create more enzyme…) Allosteric regulation (using inhibitors and activators)

Feedback Inhibiation Most reactions in living organisms are not completed in one step, and involve biochemical pathways  - sometimes the product from one step can become the substrate of the next. In some cases, the product of a later reaction can act as an allosteric inhibitor for an earlier enzyme. This is termed feedback inhibition. http://highered.mheducation.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120070/bio10.swf::Feedback+Inhibition+of+Biochemical+Pathways

Review What factors influence enzyme activity? Why does temperature affect enzyme activity? What is a cofactor? Do some research to find an example of one. How do competitive and non-competitive inhibition differ? What is feedback inhibition? Enzymes in the testicles of males are responsible for both sperm and hormone production. Some of these enzymes have an optimal temperature of 33ᵒC What anatomical features help the testicles maintain this temperature? How does this relate to the idea that structure and function are related?