Glossary
Activation Energy
The minimum amount of energy required for a chemical reaction to proceed.
Example:
Enzymes lower the activation energy for reactions, allowing processes like breaking down food to occur rapidly at body temperature.
Active Site
The specific region on an enzyme where the substrate binds and the chemical reaction takes place.
Example:
In the enzyme lactase, the active site is precisely shaped to bind to lactose, allowing it to break down this sugar.
Allosteric Regulation
The regulation of an enzyme's activity by the binding of a molecule to a site other than the active site, which can either activate or inhibit the enzyme.
Example:
In glycolysis, ATP can bind to an allosteric site on phosphofructokinase, inhibiting its activity when energy levels are high.
Catalysts
Substances that increase the rate of a chemical reaction by lowering the activation energy, but are not themselves changed or used up in the reaction.
Example:
A platinum surface acts as a catalyst in a car's catalytic converter, converting harmful exhaust gases into less toxic substances.
Denature
The process by which a protein loses its native three-dimensional structure, often due to extreme conditions like high temperature or pH, leading to a loss of function.
Example:
When you cook an egg, the heat causes the proteins in the egg white to denature, changing from clear liquid to solid white.
Enzymes
Biological macromolecules, primarily proteins, that act as catalysts to speed up the rate of biochemical reactions without being consumed in the process.
Example:
During digestion, the enzyme amylase breaks down complex carbohydrates into simpler sugars, allowing your body to absorb nutrients efficiently.
Induced Fit
A model of enzyme-substrate interaction where the active site of the enzyme undergoes a conformational change upon substrate binding, enhancing the fit and catalytic efficiency.
Example:
When glucose binds to the enzyme hexokinase, the enzyme's active site subtly reshapes to snugly embrace the substrate, illustrating induced fit.
Inhibitors
Molecules that decrease the rate of an enzyme-catalyzed reaction, often by binding to the enzyme and preventing substrate binding or catalysis.
Example:
Many medications, like statins that lower cholesterol, act as inhibitors by blocking the activity of specific enzymes in metabolic pathways.
Primary Structure
The unique, linear sequence of amino acids that forms a polypeptide chain.
Example:
The specific order of amino acids in a protein like insulin is its primary structure, which dictates how it will fold into its functional shape.
Quaternary Structure
The arrangement of multiple polypeptide subunits to form a functional protein complex.
Example:
Hemoglobin, which carries oxygen in red blood cells, is composed of four polypeptide chains interacting together, demonstrating quaternary structure.
Secondary Structure
Local folded structures that form within a polypeptide due to hydrogen bonding between atoms of the polypeptide backbone, commonly forming alpha-helices or beta-sheets.
Example:
The spiral shape of an alpha-helix in a keratin protein, giving hair its elasticity, is an example of secondary structure.
Specificity
The characteristic of enzymes to catalyze only certain reactions or bind only to certain substrates due to the unique complementary shape of their active site.
Example:
The high specificity of DNA polymerase ensures that it only adds the correct nucleotides during DNA replication, preventing errors.
Substrate
The specific molecule or molecules upon which an enzyme acts.
Example:
For the enzyme sucrase, the substrate is sucrose, which it breaks down into glucose and fructose.
Tertiary Structure
The overall three-dimensional shape of a single polypeptide chain, resulting from interactions between the R-groups of amino acids.
Example:
The complex, globular shape of an enzyme like lysozyme, allowing it to fit its substrate, represents its tertiary structure.