Figure 6.18: The Molecular Structure of Chlorophyll Chlorophyll consists of a complex ring structure (green) with a magnesium ion at its center, plus a hydrocarbon “tail.” The tail anchors chlorophyll molecules to integral membrane proteins in the thylakoid membrane. Chlorophyll a and chlorophyll b are identical except for the replacement of a methyl group (—CH3) with an aldehyde group (—CHO), shown on the upper right side of the ring structure.