Final answer:
Enzymes are proteins that speed up chemical reactions by lowering the activation energy. They are composed of amino acids, are not consumed during reactions, and are specific to their substrates.
Step-by-step explanation:
The true statement about enzymes is that they are proteins. Enzymes are essential biological catalysts that significantly accelerate the rate of chemical reactions within living organisms. They achieve this by lowering the activation energy required for a reaction to occur, thus increasing the reaction rate. While enzymes are predominantly made of amino acids, some ribozymes are composed of nucleic acids. However, when looking at traditional enzymatic functions, enzymes are not carbohydrates, lipids, or nucleic acids. In fact, specialized types of enzymes known as hydrolases play crucial roles in digesting various macromolecules: lipases hydrolyze lipids, proteases hydrolyze proteins, and nucleases hydrolyze nucleic acids.
It's also important to note that enzymes are not consumed by the reactions they catalyze, which means they can be used repeatedly to catalyze multiple reactions. Furthermore, enzymes are specific to the substrates they bind to, meaning that each enzyme is tailored to assist a particular reaction involving specific substrate(s).