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CHAPTER 2.4 CHEMICAL REACTIONS AND ENZYMES
Transcript of CHAPTER 2.4 CHEMICAL REACTIONS AND ENZYMES
Living things are made up of chemical compounds, but chemistry isn’t just what life is made of—chemistry is also what life does.
What happens to chemical bonds during chemical reactions?
Chemical reactions involve changes in the chemical bonds that join atoms in compounds
A chemical reaction is a process that changes, or transforms, one set of chemicals into another by changing the chemical bonds that join atoms in compounds.
Mass and energy are conserved during chemical transformations, including chemical reactions that occur in living organisms.
Reactants The elements or compounds that enter into a chemical reaction
Products: The elements or compounds produced by a chemical reaction
ENERGY IN REACTIONS
How do energy changes affect whether a chemical reaction will occur?
Chemical reactions that release energy often occur on their own, or spontaneously.
Chemical reactions that absorb energy will not occur without a source of energy.
Energy is released or absorbed whenever chemical bonds are formed or broken during chemical reactions.
An example of an energy-releasing reaction is the burning of hydrogen gas, in which hydrogen reacts with oxygen to produce water vapor.
The energy is released in the form of heat, and sometimes when hydrogen gas explodes light and sound.
The reverse reaction, in which water is changed into hydrogen and oxygen gas, absorbs so much energy that it generally doesn’t occur by itself.
2H2O + energy 2 H2 + O2
The only practical way to reverse the reaction is to pass an electrical current through water to decompose water into hydrogen gas and oxygen gas.
Thus, in one direction the reaction produces energy, and in the other direction the reaction requires energy.
Every organism must have a source of energy to carry out the chemical reactions it needs to stay alive.
Plants:trap and store the energy from sunlight in energy-rich compounds.
Animals:consume plants or other animals.
Humans: release the energy needed to grow, breathe, think, and even dream through the chemical reactions that occur when we metabolize, or break down, digested food.
The energy that is needed to get a reaction started is called the activation energy.
Activation energy is involved in chemical reactions whether or not the overall reaction releases or absorbs energy
What role do enzymes play in living things and what affects their function?
Enzymes speed up chemical reactions that take place in cells.
Temperature, pH, and regulatory molecules can affect the activity of enzymes.
Some chemical reactions are too slow or have activation energies that are too high to make them practical for living tissue
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
Enzymes act by lowering the activation energies, which has a dramatic effect on how quickly reactions are completed
Enzymes are very specific, generally catalyzing only one chemical reaction.
Part of an enzyme’s name is usually derived from the reaction it catalyzes.
ENZYME SUBSTRATE COMPLEX
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 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
The substrates bind to a site on the enzyme called the active site
The active site and the substrates have complementary shapes
The fit is so precise that the active site and substrates are often compared to a lock and key
REGULATION OF ENZYMES
Enzymes produced by human cells generally work best at temperatures close to 37°C, the normal temperature of the human body
Enzymes work best at certain pH values. For example, the stomach enzyme pepsin, which begins protein digestion, works best under acidic conditions
The activities of most enzymes are regulated by molecules that carry chemical signals within cells, switching enzymes “on” or “off” as needed