Ever wonder why Spock has green blood? Ask an avid Star Trek fan and they will tell you it’s because his Vulcan haemoglobin, the protein in blood cells that carries oxygen, is based on copper. Human haemoglobin (depicted here in a painting by Irving Geis) is however based on iron. Each haemoglobin molecule is constructed of four identical building blocks made of globin protein (purple) and heme (red). It is the heme group that gives our blood its distinctive red colour. Each heme contains an iron atom surrounded by a ring structure called porphyrin. When porphyrin is bound to iron carrying oxygen, it produces a red colour. While evolution paired up porphyrins with iron in humans, the same is not true for all creatures on earth. Molluscs, like Spock, also use copper giving their porphyrins a green hue.
Written by Lux Fatimathas
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.