FIGURE 2 Translation is a linear process, occurring in the N- to C-terminal direction. The experiment starts with red blood cells containing hemoglobin (Hb) that is uniformly labeled with [¹⁴C]leucine. [³H]Leucine is then added, and the cells are incubated for different times before stopping the reaction. The hemoglobin is then digested with proteases, and peptide fragments are identified by electrophoresis. Fragments at the end of the protein have a higher ³H:¹⁴C ratio (as shown by the open circles in the graph), demonstrating that protein synthesis is linear. If protein synthesis were random, the ³H:¹⁴C ratio would be constant over the length of the protein (dashed line).