Conceptual Demography in Upper Secondary Chemistry and Biology Textbooks' Descriptions of Protein Synthesis: A Matter of Context?

This study investigates how the domain-specific language of molecular life science is mediated by the comparative contexts of chemistry and biology education. We study upper secondary chemistry and biology textbook sections on protein synthesis to reveal the conceptual demography of concepts central to the communication of this subject. The term "conceptual demography" refers to the frequency, distribution, and internal relationships between technical terms mediating a potential conceptual meaning of a phenomenon. Data were collected through a content analysis approach inspired by text summarization and text mining techniques. Chemistry textbooks were found to present protein synthesis using a mechanistic approach, whereas biology textbooks use a conceptual approach. The chemistry texts make no clear distinction between core terms and peripheral terms but use them equally frequently and give equal attention to all relationships, whereas biology textbooks focus on core terms and mention and relate them to each other more frequently than peripheral terms. Moreover, chemistry textbooks typically segment the text, focusing on a couple of technical terms at a time, whereas biology textbooks focus on overarching structures of the protein synthesis. We argue that it might be fruitful for students to learn protein synthesis from both contexts to build a meaningful understanding.

Characterization of a cytochrome c gene located at the gene cluster for chlorate respiration in Ideonella dechloratans.

Anaerobic chlorate respiration requires electron transport from the bacterial inner membrane to the soluble periplasmic chlorate reductase. We have recently demonstrated that soluble c cytochromes function as electron carriers for chlorate reduction in Ideonella dechloratans (Smedja Bäcklund et al. 2009). In the present work, we describe a gene encoding soluble c-type cytochrome [cyt; GenBank ID: EU768872] located close to the gene cluster for chlorate reduction in I. dechloratans. The predicted amino acid sequence does not match any of the peptide masses or partial sequences obtained earlier from periplasmic c cytochromes. The gene, without the predicted signal sequence, was expressed heterologously in E. coli and the recombinant protein was purified, refolded and reconstituted with heme. The reconstituted protein shows spectral properties characteristic for c cytochromes, with an absorption maximum at 553 nm for the alpha band in the reduced state. Pyridine hemochrome analysis demonstrates the formation of covalently bound heme.