a. Reaction scheme. X’s represent the products, W’s the waste products. The final flux (in this five step reaction I5) is the fitness of a given cell. b. Relative orientation of enzyme-substrate complex. If the functional groups totally match and the distance between the faces (R
) are at the optimal value of the van der Waals interaction (Ropt, marked by dashed line) the conversion has the highest activity (top right). If the enzyme is larger the conversion yield reduces (top left), if the enzyme is too small the substrate is sterically excluded (bottom left). If the functional groups differ in two functional groups the enzyme catalyses waste production (bottom right). c. independently replicating genes and random assortment to daughter cells (specialist enzymes in green and red); d. generalist enzymes; and e. protocell with a chromosome and accurate segregation mechanism attached to cell boundary (blue). Fitter protocells are marked by thicker boundaries.