How can one measure the speed of a ribosome? One option is to use a microscope. Take some human cells and add 'loops' of RNA to them. Each loop has 321 codons and encodes ten copies of a small peptide, called a SunTag. These RNA loops do not have a stop codon. Ribosomes in the cell grab onto them, begin translation, and then go around the loop again and again. Each time a ribosome completes one cycle, it makes ten SunTags. As soon as a SunTag is made, it 'sticks' to the ribosome; there is no stop codon to trigger its release. Then, this SunTag gloms onto an antibody, fused to GFP, floating nearby. As the ribosome goes around the loop, its chain of SunTag grows longer. More copies of GFP grab onto the peptide chain, and the perceived brightness of the ribosome, when viewed under the microscope, grows accordingly. By measuring how quickly the ribosome's brightness changes, one can calculate its speed: First, figure out the brightness of a single GFP. You can do this as a control experiment. Then, knowing that a single loop has 321 codons, and that this creates 10 SunTags, you can deduce that one SunTag (and thus one GFP) corresponds to 32 codons. Finally, by watching the brightness change over time in steps, or chunks, and multiplying by 32, you can back-calculate to figure out how many amino acids are added by the ribosome each second. The answer, in this experiment, is 2.6. Video below. Green is the GFP. Red is a tag for the RNA loops.