Glossary
ATP Hydrolysis
The chemical reaction in which ATP (adenosine triphosphate) is broken down by water, releasing a significant amount of energy that can be used to power cellular processes.
Example:
Muscle contraction is powered by the energy released from ATP hydrolysis, allowing myosin heads to pull on actin filaments.
Activation Energy
The minimum amount of energy required for a chemical reaction to proceed. Enzymes lower this energy barrier, allowing reactions to occur more quickly.
Example:
Imagine pushing a boulder up a hill; the height of the hill represents the activation energy that enzymes reduce, making it easier to start the reaction.
Active Site
A specific region on an enzyme where the substrate binds and where catalysis occurs. Its unique shape and chemical properties are complementary to the substrate.
Example:
The precise fit between a key and a lock is analogous to how a substrate fits into an enzyme's active site.
Catalyst
A substance that increases the rate of a chemical reaction without undergoing any permanent chemical change itself. In biology, enzymes serve as biological catalysts.
Example:
In a car's catalytic converter, platinum acts as a catalyst to convert harmful exhaust gases into less toxic substances.
Competitive Inhibitors
Molecules that reduce an enzyme's activity by binding directly to its active site, thereby competing with the substrate for binding.
Example:
Some medications act as competitive inhibitors by blocking the active site of bacterial enzymes, preventing the bacteria from synthesizing essential molecules.
Denaturation
A process in which a protein, such as an enzyme, loses its characteristic three-dimensional structure due to extreme conditions like high temperature or pH, leading to a loss of its biological function.
Example:
Boiling an egg causes the proteins in the egg white to undergo denaturation, changing from clear liquid to solid white.
Enzyme-Substrate Complex
A temporary molecule formed when an enzyme binds to its specific substrate(s) at the active site. This complex facilitates the chemical reaction.
Example:
When glucose binds to hexokinase, they form an enzyme-substrate complex that allows the phosphorylation of glucose to occur.
Enzymes
Biological catalysts, typically proteins, that speed up the rate of specific biochemical reactions without being consumed in the process. They are essential for nearly all cellular functions.
Example:
Lactase is an enzyme that helps break down lactose in dairy products, allowing individuals to digest milk sugars.
Metabolism
The sum of all chemical reactions that occur within a living organism to maintain life. These processes involve the breakdown of molecules for energy and the synthesis of molecules necessary for life.
Example:
When you eat a meal, your body's metabolism breaks down the food into smaller molecules to fuel cellular activities and build new tissues.
Noncompetitive Inhibitors
Molecules that reduce an enzyme's activity by binding to a site other than the active site, which causes a conformational change in the enzyme and reduces its ability to bind to the substrate or catalyze the reaction.
Example:
Heavy metals can act as noncompetitive inhibitors by binding to various parts of an enzyme, distorting its shape and impairing its function.
Steady State
A condition in living systems where the rate of input of energy and matter equals the rate of output, maintaining a relatively constant internal environment despite continuous changes.
Example:
A cell maintains a steady state by constantly importing nutrients and exporting waste products, ensuring its internal conditions remain stable for optimal function.
Substrate
The specific reactant molecule(s) upon which an enzyme acts. Enzymes bind to their substrates at the active site.
Example:
For the enzyme amylase, starch is the substrate that it breaks down into smaller sugar molecules.