Protein targeting in cells. Illustration of routes followed by proteins in cells. In the cell nucleus (upper centre), DNA is transcribed to form mRNA (both yellow). The mRNA is used by ribosomes (red) to create proteins (green, centre). Protein destinations are the cell fluid (cytosol), the nucleus, chloroplasts (green, centre left), a mitochondrion (orange, lower centre), and a peroxisome (blue, bottom right). One major pathway is to the endoplasmic reticulum (pink, lower right) and the Golgi apparatus, emerging to be sorted in vesicles and lysosomes (upper right) for release outside the cell by exocytosis. For this artwork without labels, see C023/8877.