Enzymes are molecules that accelerate, or catalyze, chemical reactions. In these reactions, the molecules at the beginning of the process are called substrates and the enzyme converts these into different molecules, called products. Almost all metabolic processes in the cell need enzymes in order to occur at rates fast enough to sustain life. The set of enzymes made in a cell determines which metabolic pathways occur in that cell. The study of enzymes is called enzymology.

Méisù shì yīzhǒng fēnzǐ, yòngyǐ cùjìn huò cuīhuà huàxué fǎnyìng. Fǎnyìng chūqī de fēnzǐ chēngwéi dǐcéng wùzhì, ránhòu zhuǎnhuà wéi bùtóng de fēnzǐ, jiàozuò chǎnpǐn. Jīhū suǒyǒu xìbāo de xīnchéndàixiè dōu xūyào méisù cuīhuà, yǐ wéichí shēngmìng. Xìbāo de méisù juédìng xīnchéndàixiè de fāngshì. Méisù de yánjiū chēngwéi méisùxué.