From Fig. , we see that the number of CO2 molecules that bind to rubisco far exceed the number of CO2 molecules that hit the carboxysome surface. However, the numbers are comparable, with the binding rate of CO2 to rubisco only 2.3 (± 0.05) times higher than the rate at which CO2 hits the carboxysome surface. If this were the final number, appreciable CO2 would leak out of the carboxysome during carbon fixation, and represents the scenario where the rubisco core was intact but the shell was absent. From Fig. derived from our atomic simulations, we see that a typical CO2 molecule is reflected by the shell many times before leaving the shell. Indeed, not shown in Fig. are the many molecules that strike the carboxysome surface and never cross during our relatively short atomistic simulations. If we focus only on CO2 molecules that are initially inside the synthetic carboxysome in our atomistic simulations, 72 will cross the carboxysome during . Most of the CO2 that is generated by carbonic anhydrase will quickly find a rubisco active site on a microsecond timescale (Fig. ), with kinetics effectively limited by how quickly generated CO2 can diffuse to an active site. The diffusion is assisted by the multiple reflections from the shell surface that a CO2 particle can experience before it finds a pathway to escape the carboxysome, creating an effective CCM even in a nominally leaky carboxysome shell.