Proteins are essential for cell function, and their biological performance depends on three-dimensional (3D) structures. Insulin is made up of 51 amino acids and is a critical hormone involved in glycaemia regulation. In basic education, concepts involving proteins (synthesis, structure, interactions, and function) are abstract and difficult for students to understand. The use of protein 3D models that assist in visualising biomolecular structures can be an important didactic tool to understand the complexity of protein structure. Here, we propose a practical activity for the construction of a 3D model of insulin, as a tool for teaching protein synthesis and structure to students in the 9th-grade of basic education. The activity involved three classes of one hour each. 62 students role-played the insulin mRNA translation and represented the primary structure through balloons tied to a string. They also built an 3D insulin model using Styrofoam balls and wire. The activities proved to be effective, as there was a better understanding by students regarding proteins and their characteristics. Therefore, practical classes for teaching proteins can be used in basic education to improve learning of abstract and sub-microscopic concepts.