Past exam of the biochemistry and Molecular Biology course of the University of Cambridge / 2025 / Paper 2 / Section B / 11 / e

The dilution in the Bradford assay is $1000/5=200$. Read the fitted line rather than assuming it passes through the origin: the two absorbances correspond approximately to $4.3$ and $15\mu \mathrm{g}\mathrm{m}{\mathrm{L}}^{-1}$ in the assay mixture. ThereforeMultiplying by the $0.500\mathrm{mL}$ eluate volume gives about $0.43\mathrm{mg}$ of TEM-1 and $1.5\mathrm{mg}$ of TEM-52. Only TEM-52 meets the requirement.

Assuming the same recovery per culture volume, the required volumes areUse approximately $120\mathrm{mL}$ or more for TEM-1; the existing $50\mathrm{mL}$ is sufficient for TEM-52. Rounding the former up to $125\mathrm{mL}$ is sensible given graphical precision. Reading the lower standard as $4$–$4.5\mu \mathrm{g}\mathrm{m}{\mathrm{L}}^{-1}$ gives a corresponding requirement of roughly $110$–$125\mathrm{mL}$, not an exact integer volume. These estimates assume comparable dye response to bovine serum albumin, suitable buffer blanks and that recovered protein is the purified target; contaminants would inflate the inferred target yield.