9: Catalysis
- Page ID
- 150424
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- 9.1: A. Methods of Catalysis
- Catalysts, including enzymes, can employ at least five different ways to stabilize transition states. Reactions in solution that are not catalyzed are slow since charge development and separation occurs in the transition state. When bonds are made or broken, charged intermediates are often formed which are higher in energy than the reactants. Since the intermediate is higher in energy than the reactants, the transition state would be even higher in energy, and hence more closely resemble the cha
- 9.2: B. Mechanisms of Enzyme-Catalyzed Reactions
- We can apply what we learned about catalysis by small molecules to enzyme-catalyzed reactions. To understand the mechanism of an enzyme-catalyzed reaction, we try to alter as many variables, one at a time, and ascertain the effects of the changes on the activity of the enzyme. Kinetic methods can be used to obtain data from which inferences about the mechanism can be made. Obviously, crystal structures of the enzyme in the presence and absence of a competitive inhibitor gives useful information.
- 9.3: Sources and Sinks
- To make and break bonds, electrons have to be moved. In drawing reaction mechanisms, we showed how electrons moved from "sources" to "sinks". In many enzyme-catalyzed reactions, vitamin derivatives are uses as substrates or "cofactors" or "coenzymes" to facilitate the flow of electrons in bond making and breaking. For each of the reactions below, using the analogy of source/sink, write a reasonable mechanism which shows electron flow during the reaction.
- 9.4: D. Enzyme Catalyzed Reactions in Organic Solvents
- In the previous chapter, I showed how you could obtain information about the enzyme by changing the substrate, pH, and the enzyme. Why not change the solvent? Attempts have been made to do this for the last 100 years.
- 9.5: E. Ribozymes and the RNA World
- Protein can fold to form unique 3D structures which can have active sites with appropriate functional groups or nonprotein "cofactors" (metal ions, vitamin derivatives) that participate in catalysis. There is nothing special about the ability of proteins to do this. It is now known that RNA, which can form complicated secondary and tertiary structures (Ribozymes).
Thumbnail: Enzyme changes shape by induced fit upon substrate binding to form enzyme-substrate complex. Hexokinase has a large induced fit motion that closes over the substrates adenosine triphosphate and xylose. Binding sites in blue, substrates in black and Mg2+ cofactor in yellow. (PDB: 2E2N, 2E2Q). Image used with permission (CC BY 4.0l Thomas Shafee).