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Chlorophyll


Chlorophyll

Ancient Greek: chloros = green and phyllon = leaf. It is a green photosynthetic pigment found in plants, algae, and cyanobacteria. The first step in photosynthesis is when incoming light is absorbed by chlorophyll, ionizing it. The resulting chemical energy is then captured in the form of ATP, and ultimately to convert carbon dioxide and water to carbohydrates and oxygen. Chlorophyll absorbs most in the red and blue portions of the electromagnetic spectrum, thus its intense green color.

Chemical structure

Chlorophyll is a chlorin pigment, which is structurally similar to porphyrin pigments such as heme. At the center of the chlorin ring is an magnesium ion. This has various side chains, usually including a long phytyl chain. There are a few different forms that occur naturally:

Chlorophyll a Chlorophyll b Chlorophyll c1 Chlorophyll c2 Chlorophyll d
Molecular formula C55H72O5N4Mg C55H70O6N4Mg C35H30O5N4Mg C35H28O5N4Mg C54H70O6N4Mg
C3 group -CH=CH2 -CH=CH2 -CH=CH2 -CH=CH2 -CHO
C7 group -CH3 -CHO -CH3 -CH3 -CH3
C8 group -CH2CH3 -CH2CH3 -CH2CH3 -CH=CH2 -CH2CH3
C17 group -CH2CH2COO-Phytyl -CH2CH2COO-Phytyl -CH=CHCOOH -CH=CHCOOH -CH2CH2COO-Phytyl
C17-C18 bond Single Single Double Double Single
Occurrence Universal Mostly in land plants Various algae Various algae Some red algae
Common structure of chlorophyll a, b and d

Evidence for chlorophyll

Absorbance spectra of by chlorophyll a (green) and b (red)

Chlorophyll can be shown to be vital for photosynthesis by destarching a leaf from a variegated plant and exposing it to light for several hours. (Variegated leaves have green areas that contain chlorophyll and white areas that have none.) When tested with iodine solution , a color change revealing the presence of starch occurs only in regions of the leaf that were green and therefore contained chlorophyll. This shows that photosynthesis does not occur in areas where chlorophyll is absent and constitutes evidence that the presence of chlorophyll is a requirement for photosynthesis.


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