The aim of this licentiate thesis is to contribute to understanding of upper secondary teaching and learning of protein synthesis with a focus on domain-specific language. It is based on two studies, designated Studies I and II. Study I addressed upper secondary students’ understanding of protein synthesis through their usage of domain-specific concepts. Data collected through semi-structured group interviews show that students can better reason about core concepts than peripheral concepts, and they compartmentalise the concepts into five clusters. Study II focused on chemistry and biology textbooks’ presentation of protein synthesis through domain-specific concept usage and effects of context on these presentations. The textbooks were analysed using a content analysis approach involving data mining techniques implemented by a computer-generated algorithm. The results reveal that chemistry textbooks focus more on peripheral concepts and generally tend to identify fewer relationships among more concepts than biology textbooks, which emphasise core concepts and tend to highlight more relationships among fewer concepts. Jointly, Studies I and II reveal four facets of teaching and learning protein synthesis: ‘mechanistic or conceptual descriptions’, ‘compartmentalisation’, ‘mRNA as a core concept’ and ‘canonical representation’. By acknowledging the results reported herein, teaching can improve the facilitation and reduce the hindrance in learning protein synthesis through the awareness of the domain-specific language usage. / Proteins are crucial to life: no proteins – no life. Every picosecond, thousands of proteins are constructed in each cell in what is referred to as protein synthesis. Due to its importance for understanding the mechanism for life, protein synthesis is globally regarded as a cornerstone of molecular life sciences and education in the field. Like any area of expertise, the molecular life sciences share a domain-specific language. However, research on teaching and learning protein synthesis through this domain-specific language is scarce. The aim of this licentiate thesis is thereby to contribute to understanding of upper secondary teaching and learning of protein synthesis with a focus on domain-specific language. The thesis is based on two studies: Study I addressed students’ understanding where the results show that students can better reason about core concepts than peripheral concepts, and they compartmentalise the concepts into five clusters. Study II focused on chemistry and biology textbooks’ presentation and effects of context on these presentations. The results reveal that chemistry textbooks focus more on peripheral concepts and generally tend to identify fewer relationships among more concepts than biology textbooks, which emphasise core concepts and tend to highlight more relationships among fewer concepts. Jointly, Studies I and II reveal four facets of teaching and learning protein synthesis. By acknowledging the results reported herein, teaching can improve the facilitation and reduce the hindrance in learning protein synthesis through the awareness of the domain-specific language usage.