The correct answer is option 2: Proteins. Enzymes are a type of protein, which means that they are made up of long chains of amino acids. Proteins are essential for many biological processes in the body, including serving as enzymes. Enzymes are catalysts that speed up chemical reactions in living organisms without being consumed or changed in the process.

Options 1, 3, and 4 are incorrect. Alkaloids are a diverse group of naturally occurring compounds that are often derived from plants, and they do not have the same properties or functions as enzymes. Carbohydrates are a different class of biomolecules that serve as a source of energy and provide structural support in cells, but they are not enzymes. Lipids, another category of biomolecules, include fats, oils, and some hormones, but they are not enzymes either.

It is important to note that while all enzymes are proteins, not all proteins are enzymes. Proteins have many other important functions in the body, such as providing structure to cells, transporting molecules, and carrying out signaling pathways, but only a subset of proteins have enzymatic activity.