Enzymes

• Catalyst


  A substance that helps a chemical reaction to occur
• special molecules that catalyze biochemical reactions are 


  enzymes
• Almost all enzymes are proteins, comprised of amino acid chains, and they perform the critical task of lowering the activation energies of chemical reactions inside the cell.
• Enzymes do this by binding to the reactant molecules, and holding them in such a way as to make the chemical bond-breaking and bond-forming processes take place more readily.
• enzymes do not change the reaction's ∆G


  they do not change whether a reaction is exergonic (spontaneous) or endergonic. This is because they do not change the reactants' or products' free energy. They only reduce the activation energy required to reach the transition state
• chemical reactants to which an enzyme binds are the enzyme’s substrates
• may be one or more substrates, depending on the particular chemical reaction
• some reactions = single-reactant substrate breaks down into multiple products. others = 2 substrates may come together to create one larger molecule. Two reactants might also enter a reaction, both become modified, and leave the reaction as two products.
• Enzymes + Substrates summary


  each enzyme has an active site, which is where the reaction takes place. These sites are like special pockets that are able to bind a chemical molecule. The compounds or molecules the enzyme reacts with are called their substrates.
• Location within the enzyme where the substrate binds.This is where the “action” (reaction) happens.


  Active Site
• Since enzymes are proteins, there is a unique combination of amino acid residues (also side chains, or R groups) within the active site. Different properties characterize each R group.
• Unique combo creates specific chemical environment within the active site, which is suited to bind to specific substrate(s).
• enzymes are known for their specificity
• “best fit” results from the shape and the aa functional group’s attraction to the substrate.
• Active sites are subject to local environmental influences


  increasing or decreasing the temperature outside of an optimal range can affect chemical bonds within the active site in such a way that they are less suited to bind substrates.
• High temperatures will eventually cause enzymes (other biological molecules too) to denature, a process that changes the substance's natural properties.
• local environment's pH can also affect enzyme function. Active site amino acid R-groups have their own acidic/basic properties that are optimal for catalysis which

  are sensitive to changes in pH that can impair the way substrate molecules bind.
• Enzymes are suited to function best within a certain pH range, and, as with temperature, extreme environmental pH values (acidic or basic) can cause enzymes to denature.
• induced fit

  enzyme and substrate come together causing a mild shift in the enzyme’s structure. This confirms an ideal binding arrangement between the enzyme and the substrate's transition state. This ideal binding maximizes the enzyme’s ability to catalyze its reaction.
• When an enzyme binds its substrate, it forms an enzyme-substrate complex.
• Enzyme-Substrate Complex


  lowers the reaction's activation energy and promotes its rapid progression in one of many ways. It can lower the activation energy by contorting substrate molecules in such a way as to facilitate bond-breaking, helping to reach the transition state.
• enzymes promote chemical reactions that involve more than one substrate by bringing the substrates together in an optimal orientation. 


  one way enzymes promote substrate reaction
• 2nd way enzymes promote substrate reaction 


  creating an optimal environment within the active site for the reaction to occur. Certain chemical reactions might proceed best in a slightly acidic or non-polar environment. The chemical properties that emerge from the particular arrangement of aa R-groups within an active site create perfect env.
• enzymes can also lower activation energies by taking part in the chemical reaction itself. The amino acid residues can provide certain ions or chemical groups that form covalent bonds with substrate molecules as a necessary step of the reaction process. In these cases, it is important to remember that the enzyme will always return to its original state at the reaction's completion.
• One of enzymes' hallmark properties is that they remain ultimately unchanged by the reactions they catalyze. After an enzyme catalyzes a reaction, it releases its product(s).
• Cellular needs and conditions vary from cell to cell, and change within individual cells over time. This is why enzymes in genomes are not in abundant supply or function well under all conditions.
• amounts + functioning of the variety of enzymes within a cell determine which reactions will proceed and at which rates because rates of biochemical reactions are controlled by activation energy, and enzymes lower and determine activation energies for chemical reactions.
• Enzymes can be regulated in ways that either promote or reduce their activity.
• Competitive inhibition


  an inhibitor molecule competes with the substrate for active site binding. inhibitor molecule is similar enough to a substrate that it can bind to the active site and block the substrate from binding.
• Enzyme inhibitors


  molecules that interact with enzymes (temporary or permanent) in some way and reduce the rate of an enzyme-catalyzed reaction or prevent enzymes to work in a normal manner
• Noncompetitive Competition


  an inhibitor molecule binds to the enzyme in a location other than the active site, called an allosteric site, but still manages to prevent substrate binding to the active site. Some inhibitor molecules bind to enzymes in a location where their binding induces a conformational change that reduces the enzyme activity as it no longer effectively catalyzes the conversion of the substrate to product.
• Brief Summary

  A substrate enters the active site of the enzyme. This forms the enzyme-substrate complex.The reaction then occurs, converting the substrate into products and forming an enzyme products complex. The products then leave the active site of the enzyme.
• allosteric inhibition

  When some inhibitor molecules bind to enzymes in a location where their binding induces a conformational change that reduces the enzyme's affinity for its substrate.
• Allosteric Activators

  bind to locations on an enzyme away from the active site, inducing a conformational change that increases the affinity of the enzyme’s active site(s) for its substrate(s).
• Reversible Inhibition 


  Competitive & Non-competitive Inhibitition
• Enzyme Helper

  • may bind to enzyme or substrate to help goal of reaction
• coenzymes

  helpers which bind to enzymes and help them function, organic (vit=coenzymes)
• cofactors

  inorganic, trace metals that we eat (magnesium,zinc,iron) helping processes to occur
• Feedback inhibition

  using a reaction product to regulate its own further production. Cell slows down production during anabolic or catabolic reactions as a response to abundance of specific products. These products may inhibit the enzymes that catalyzed their production