Chemical Reactions and Enzymes The Chemistry of Life Chemical Reactions and Enzymes

Chemical Reactions Everything that happens in an organism – it’s reproduction, its interactions with the environment, and even its movement – is based on chemical reactions.

Chemical Reactions A chemical reaction is a process that changes, or transforms, one set of chemicals into another. An important scientific principle is that mass and energy are conserved during chemical transformations.

The parts of a chemical reaction Reactants: the elements or compounds that enter into a chemical reaction Products: the elements or compounds produced by a chemical reaction For example: carbon dioxide and water reaction in the blood stream to produce carbonic acid, which enables it to be carried to the lungs CO2 + H2O H2CO3

Energy in Reactions Energy is released or absorbed whenever chemical bonds form or are broken. Because chemical reactions involve breaking and forming bonds, they involve changes in energy. Chemical reactions that release energy often occur spontaneously, but not always. Chemical reactions that absorb energy will not occur without a source of energy.

Energy in Reactions Activation Energy: the energy that is needed to get a reaction started Products Products Reactants Activation Energy Reactants Activation Energy

Energy in Reactions Activation energy is a factor in whether the overall chemical reaction releases energy or absorbs it.

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Enzymes Some chemical reactions that make life possible are too slow or have activation energies that are too high to make them practical for living tissues. These reactions are made possible by catalysts.

Enzymes A catalyst is a substance that speeds up the rate of a chemical reaction by lowering a reaction’s activation energy. Enzymes are proteins that act as biological catalysts. They speed up chemical reactions that take place in cells. Lowering the activation energy has a dramatic effect on how quickly the reaction is completed.

Enzymes Activation energy without enzyme Activation energy with enzyme

Enzymes Enzymes are very specific, generally catalyzing only one chemical reaction. For this reason, part of an enzyme’s name is usually derived from the reaction it catalyzes. Enzymes end in –ase.

Enzymes For a chemical reaction to take place, the reactants must collide with enough energy so that existing bonds will be broken and new bonds will be formed. If the reactants do not have enough energy, they will be unchanged after the collision.

Enzymes Enzymes provide a site where reactants can be brought together to react. Such a site reduces the energy needed for reaction. The reactants of enzyme-catalyzed reactions are known as substrates.

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Enzymes

Enzymes The enzyme and substrate are bound together by intermolcular forces and form an enzyme-substrate complex.

Enzymes The enzyme-substrate complex remain bound together until the reaction is done. Then the products are released and the enzyme is free to start the process again. Therefore the amount of enzymes does not have to equal the amount of substrates it is acting upon.

Enzymes Because they are catalysts for reactions, enzymes can be affected by any variable that influences a chemical reaction. Some of those variable are: pH Temperature

Enzymes Cells can regulate the activation of enzymes in a variety of ways. Most cells contain proteins that help to turn key enzymes “on” or “off” at critical stages in the life of the cell.

Enzymes Enzymes play essential roles in: Regulating chemical pathways Making materials that cells need Releasing energy Transferring information

2. Substrates bind to the enzyme at the active site Products Substrate 1. Enzyme Active Site Substrate 4. Products are released 2. Substrates bind to the enzyme at the active site 3. Substrates are converted into products