Question

The shell of the cyanobacterial carboxysome described in Problem 25 is relatively impermeable to ${\mathit{O}}_{\mathbf{2}}$. Why would this be an advantage for the bacteria?

Short answer

The shell of the cyanobacterial carboxysome would be beneficial to the bacteria because it reduces the photooxidation in the bacteria.

Step-by-step solution

Ingredients of carboxysomes

Carboxysomesare proteinaceous organelles that serve a vital role in enhancing carbon fixation in proteobacteria and cyanobacteria. Carbonic anhydrase and Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is encapsulated in these organelles by a protein shell that is physically comparable to an icosahedral virus capsid.

Cause for being advantageous for bacteria

RuBisCO and carbonic anhydrase are encapsulated by a protein shell in the cyanobacterial carboxysome. This shell has moderate resistance to$O_2$. This is beneficial to the bacteria. This is because the$O_2$competes with the $C{O}_2$for the active site of the carboxylase. By reducing the presence of $O_2$, the frequency of photooxidation, or oxidation reactions that occur due to light, will be lowered. This could lead to a boost in the efficiency of carbon fixation.