Pancreatic acinar cell. Colored Transmission Electron Micrograph (TEM) of a slice through a digestive enzyme-secreting acinar cell of the human pancreas. The dark green patch in the nucleus (orange) is the nucleolus - an active area where genes are being transcribed to produce messenger molecules (mRNA). The mRNA molecules pass out of nuclear pores (red) and attach to ribosomes, the tiny dots on the intricately folded 'endoplasmic reticulum' in the cytoplasm. The ribosomes use the mRNA to synthesize the cell's output of digestive enzymes. The small red bodies are energy-producing bodies called mitochondria. Magnification unknown.