Here’s a challenge for present-day systems biologists. Say you wanted to find out how many ribosomes are present in cells growing under different conditions. How would you do it? You might think of using quantitative PCR to measure the amount of rRNA inside the cell. However, you could end up with an overestimate because some of the rRNA may not yet be assembled in mature ribosomes. For instance, add chloramphenicol, a protein synthesis-inhibiting antibiotic, to a culture and you will measure increases in the cellular levels of rRNA due to the accumulation of non-functional, immature ribosomes. Perhaps, then, you would roll up your sleeves and run a sucrose gradient to separate the mature ribosomes from their precursors and immature forms by size fractionation, but this is a labor intensive method that not many people like to do these days. We’ll agree that making such measurements may not be as easy as it sounds. So let me reminisce about how we carried this out in the old days. All it took was a fancy apparatus and some chutzpah.
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