Biochemistry · BEGINNER LESSON
Enzyme
An enzyme is usually a large protein that acts as a catalyst for a biological reaction. It binds a specific substrate at an active site and lowers the activation energy needed for the reaction to proceed.
What an enzyme is and what is measured
An enzyme is a protein made of amino acids, usually folded into a specific shape, that helps a chemical reaction happen faster in living systems. What is measured in practice is the reaction rate, meaning how quickly substrate is converted to product, and often the substrate concentration needed to reach a given rate. Enzymes are often named with the suffix -ase, and each enzyme is usually specific for one substrate or one reaction. [0,1,2]
[1] Biochemistry, Proteins Enzymes - StatPearls - NCBI Bookshelf [2] 26.10 Enzymes and Coenzymes - Organic Chemistry | OpenStax [3] Physiology, Proteins - StatPearls - NCBI Bookshelf
How enzymes work
An enzyme first binds a substrate at its active site, a groove or crevice formed by specific amino acids. This creates an enzyme-substrate complex, after which the enzyme helps form product and then releases it so the same enzyme molecule can work again. The main effect is to lower the activation energy, which means the reaction needs less energy to start. The enzyme does not change the reaction equilibrium; it only makes the forward and reverse processes happen faster. Enzymes can use several mechanisms, including temporary covalent bonding, acid-base catalysis, bringing reactants close together, and metal ions that help stabilize charge. [0,1,2]
[1] Biochemistry, Proteins Enzymes - StatPearls - NCBI Bookshelf [2] 26.10 Enzymes and Coenzymes - Organic Chemistry | OpenStax [3] Physiology, Proteins - StatPearls - NCBI Bookshelf
Why specificity matters
Specificity means that the active site fits only certain substrates well enough for catalysis. This fit depends on the shape and chemistry of the amino acids in the active site. Some descriptions use a lock-and-key idea, where shapes already match; others use induced fit, where binding helps the enzyme and substrate adjust into a productive shape. Either way, a changed active-site amino acid can reduce or abolish activity by lowering binding or preventing the needed chemistry. [0,2]
[1] Biochemistry, Proteins Enzymes - StatPearls - NCBI Bookshelf [3] Physiology, Proteins - StatPearls - NCBI Bookshelf
Cofactors, limits, and regulation
Some enzymes need a cofactor, a non-protein helper, to be active; without it, the protein part is an apoenzyme and may be inactive. A coenzyme is a type of cofactor that is itself changed during the reaction and must later be restored. Enzymes are powerful but not magical: they do not make unfavorable chemistry favorable, they do not add energy, and they do not shift equilibrium. Their rate can also be limited by inhibitors, allosteric control, mutation, or by reaching a maximum velocity when substrate is plentiful. [0,1,2]
[1] Biochemistry, Proteins Enzymes - StatPearls - NCBI Bookshelf [2] 26.10 Enzymes and Coenzymes - Organic Chemistry | OpenStax [3] Physiology, Proteins - StatPearls - NCBI Bookshelf
SEE THE IDEA
How an enzyme speeds a reaction
The starting molecule the enzyme acts on.
A matching pocket made by specific amino acids.
The bound state that helps the reaction proceed.
Product leaves and the enzyme can be used again.
Substrate binds the active site, the enzyme lowers activation energy, and product is released.
A simple cycle showing binding, catalysis, and reuse of the enzyme. [0,1,2]
TRY IT YOURSELF
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.