Benefit and cost of a protein

This is a chapter from the free textbook "Economic Principles in Cell Biology" In this chapter we discuss the cellular growth rate effects of expressing a protein. We show how protein costs and benefits can be defined and how they reflect both the protein’s molecule properties and cell-wide changes in resource allocation. For enzymes, the benefit depends on enzyme efficiencies, while protein cost depends mostly on protein size and amino acid composition, representing energy, and material needed to produce the protein, possibly conceptualized as opportunity costs. After an overview of protein production and the necessary resources, we study the optimal expression of a metabolic enzyme by a simple cost-benefit model. Then we discuss how empirical costs and benefits can be defined and measured for the Lac operon in Escherichia coli. Finally, we discuss predictions from constraint-based and mechanistic cell models. In an appendix, we give details about experimental techniques for measuring transcription and translation, controlling expression levels, and measuring growth rates.