2.4 Enzymes Flashcards
What are enzymes?
Enzymes are biological catalysts that speed up the rate of reactions, but are unused by the reaction.
Enzymes act within cells, and also involved in making the structural parts of the human body, e.g. muscles, bone and connective tissue.
Enzymes work best at a specific temperature (37 degrees for human enzymes), Normal pressure and a specific pH.
How do enzymes work?
Enzymes work by lowering the amount of activation energy needed to carry out the reaction. When the activation energy is lowered, the reaction can be carried out at a much lower temperature.
What are intracellular enzymes?
Intracellular enzymes mean they work inside the cell and catalyse metabolic reactions. One example is catalase.
What does catalase do?
catalase breaks down harmful hydrogen peroxide in the liver, forming non-harmful products - oxygen and water.
Hydrogen peroxide -> oxygen + water
What are extracellular enzymes?
Extracellular enzymes work outside of the cells. They are made inside cells and then secreted. Many of our digestive enzymes are extracellular, e.g. amylase and trypsin.
What do amylase and trypsin do?
Amylase is found in saliva in the mouth, and breaks down starch into maltose. It is also found in the small intestine.
Trypsin is found in the small intestine and breaks down protein into amino acids.
How are most enzymes named?
Most enzymes are named for their substrate:
lactase digests lactose,
maltase digests maltose,
cellulase digests cellulose
What is an inhibitor?
An inhibitor binds to the enzyme and slows down or stops the enzyme’s activity
What are competitive inhibitors?
Competitive inhibitors bind to the active site of the enzyme. They compete with the substrate for access to the active site. Once the inhibitor is bound, the substrate cannot bind.
Are competitive inhibitors reversible?
Yes, most are. When the substrate is in excess, it out-competes the inhibitor and rate of reaction returns to normal.
What are non-competitive inhibitors?
Non-competitive inhibitors bind to the enzyme’s allosteric site. When the inhibitor binds, it alters the tertiary structure and distorts the active site so that the substrate can’t bind.
Are non-competitive inhibitors reversible?
No, they are non-reversible. Many bind permanently to the enzyme. In this case we say that the enzyme is denatured.
How do inhibitors work as poisons?
They work by binding to enzymes. For example, cyanide is a non-competitive inhibitor of the enzyme cytochrome oxidase. This enzyme is essential in aerobic respiration. Cyanide poisoning is reversible, but the antidote must be given quickly.
How do inhibitors work as medicines?
Many medical drugs, such as blood pressure medicines, work by inhibiting enzymes. Angiotensin converting enzyme (ACE) inhibitors inhibit ACE. This prevents ACE from taking part in metabolic pathway that would increase pressure.
