When a metal ion is bonded in the center of an organic molecule, it is referred to as a chelate. Chlorophyll, the green pigment in plants, is one of the most important naturally-occurring chelates. The central ion in chlorophyll is magnesium, which is bonded to an organic molecule called a porphyrin, which contains four nitrogen atoms that bond with the central magnesium (to be overtly pedantic, they bond in a square planar arrangement).
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Chlorophyll absorbs in the red and blue-violet spectrum and reflects yellow-green, hence its name (from the Greek, chloros, for yellow-green).
Chlorophyll’s most extraordinary feature, of course, is its ability to absorb the energy of our sun and, through the process of photosynthesis, use the sun’s energy to transform carbon dioxide and water into carbohydrates and oxygen. The carbohydrates produced (designated below as the empirical formula (CH2O)) are the energy that fuels biochemical reactions in almost all living organisms on our planet.
CO2 + H2O → (CH2O) + O2
Chlorophyll is the catalyst in the electron transfer, oxidation-reduction reaction between carbon dioxide and water (and isn’t it grand that one of the by-products of photosynthesis is oxygen for us to breathe?).
As with many things regarding life on this planet, designs are repeated: blueprints are used over and over. For example, there are molecules with similar structures to chlorophyll that are essential in other biochemical electron-transfer (oxidation-reduction) reactions.
Heme is a close-cousin to chlorophyll with a similar porphyrin structure, but heme is bright red and has an iron(II) ion in its center. In our red blood cells, heme is bound to proteins and forms hemoglobin; which, in turn, combines with oxygen in our lungs and releases the oxygen into our tissues through the flow of blood.
Vitamin B12 (also called cobalamin), another close-cousin to chlorophyll, has a cobalt ion at the center of the porphyrin structure. B12, like heme, is bright red and is required for cellular metabolism, the formation of DNA, and energy production. B12 is not produced by higher plants, so vegetarians and vegans must ensure they consume other sources or their diet can lead to a B12 deficiency.
It never ceases to amaze me that the underlying patterns of life on this planet are so similar, or that all life on Earth is intrinsically interconnected. It’s the reason I studied bio-sciences at university (though I can’t quite explain my years studying and working with electronics and mechanical systems), and I’ll never forget Cyril, my first-year biology Professor at SFU, who, when I stared at him with the wide-eyed disbelief of thunderstruck knowledge, smiled and said to me: “So; do you believe in God?”
Thank you Cyril (and the many others), for opening my eyes to the light of knowledge.