Figure 1.

Schematic of the stages of insulin biosynthesis. 1. Insulin gene containing three exons separated by two introns. 2. Preproinsulin produced via the transcription and translation of the insulin gene. 3. Proinsulin produced from preproinsulin after the signal peptide is cleaved off by signal peptidase. 4. Mature insulin produced as the C-peptide is cleaved from proinsulin within secretory vesicles. Displayed domains: the amino-terminal (N-ter) signal peptide (red), the B-chain (yellow), the C-peptide (blue), and the carboxy-terminal (C-ter) A-chain (green).