Enzymes are proteins that catalyze chemical reactions in the body. Enzymes can increase the rate of a reaction by a factor of millions. Enzymes do this by lowering the activation energy of the reaction. The activation energy is the amount of energy needed to start a chemical reaction.
Enzymes are very specific. Each enzyme will only catalyze one reaction. Enzymes are named after the reaction they catalyze. For example the enzyme that catalyzes the breakdown of sugars is called sucrase.
Enzymes are found in all body tissues including the liver pancreas and muscles. Enzymes are also found in the cells lining the stomach and intestine.
Enzymes are made up of amino acids. There are 20 different amino acids that can be used to make enzymes. Enzymes are folded into a three-dimensional shape. This shape is determined by the sequence of amino acids.
The three-dimensional shape of an enzyme is important for its function. The shape of an enzyme will determine what substrate it can bind to. The substrate is the molecule that the enzyme will act on.
Enzymes are classified into six groups based on their function.
Catalytic enzymes
A catalytic enzyme is an enzyme that increases the rate of a chemical reaction. Catalytic enzymes lower the activation energy of the reaction.
Acyltransferases
Acyltransferases are enzymes that transfer an acyl group from one molecule to another. Acyltransferases are important in the metabolism of fats and oils.
Isomerases
Isomerases are enzymes that catalyze the rearrangement of atoms in a molecule. Isomerases are important in the metabolism of carbohydrates.
Ligases
Ligases are enzymes that join two molecules together. Ligases are important in the synthesis of DNA and RNA.
Hydrolases
Hydrolases are enzymes that catalyze the breakdown of a molecule by adding water. Hydrolases are important in the digestion of food.
Oxidoreductases
Oxidoreductases are enzymes that catalyze the transfer of electrons between molecules. Oxidoreductases are important in the metabolism of carbohydrates fats and proteins.
What are enzymes?
Enzymes are biological catalysts.
They are proteins that increase the rate of a chemical reaction without being used up in the process.
What is the active site?
The active site is the part of the enzyme that reacts with the substrate.
How do enzymes work?
Enzymes work by lowering the activation energy of a reaction.
What are substrates?
Substrates are the molecules that enzymes react with.
What is the difference between a substrate and an inhibitor?
Substrates are molecules that enzymes react with to catalyze a reaction while inhibitors are molecules that bind to enzymes and prevent them from working.
What are the conditions that affect enzyme activity?
Enzyme activity can be affected by changes in temperature pH and the concentration of substrates and inhibitors.
What happens to enzymes when they are exposed to extreme conditions?
Enzymes can be denatured by exposure to extreme conditions such as high temperatures or drastic changes in pH.
This causes the protein structure of the enzyme to change rendering it inactive.
How can enzyme activity be increased?
Enzyme activity can be increased by increasing the concentration of substrates adding inhibitors or by using a mutant enzyme with a higher affinity for the substrate.
What is a mutant enzyme?
A mutant enzyme is an enzyme that has been changed by a mutation in its gene.
What is the difference between competitive and noncompetitive inhibition?
In competitive inhibition the inhibitor competes with the substrate for binding to the active site of the enzyme.
In noncompetitive inhibition the inhibitor binds to the enzyme at a site other than the active site.
What is allosteric regulation?
Allosteric regulation is the regulation of enzyme activity by a molecule that binds to the enzyme at a site other than the active site.
What is feedback inhibition?
Feedback inhibition is a type of allosteric regulation in which the product of a reaction inhibits the enzyme that catalyzed that reaction.
What is the difference between an enzyme and a coenzyme?
Enzymes are proteins that catalyze reactions while coenzymes are small organic molecules that assist enzymes in their work.
What is a prosthetic group?
A prosthetic group is a non-protein organic molecule that is required for the activity of some enzymes.
What is the difference between a zymogen and an enzyme?
Zymogens are inactive enzymes that must be activated by a chemical reaction before they can function.
Enzymes are active from the start.
