Transitional protistans, algae, and plants all have chlorophyll: where did that pigment come from? What is?

Question

Transitional protistans, algae, and plants all have chlorophyll: where did that pigment come from? What is?

Answer 1

Before the atmosphere had oxygen all bacteria may have used electron transport across their membrane and proton pumping to make a proton gradient for ATP synthesis. This required  membrane transport proteins that could move ions and substrates into the cell. Further the cell could make heme-like ring molecules that held metal centers. These are found in cell respiration.

Early photosynthesis was more like the archaebacterium Halobacterium halobium that lacks chlorophyll and uses a rhodopsin like protein.

http://www.pubmedcentral.nih.gov/article...

Chlorophyll evolved after bacteria split from the archaebacteria because no archaebacteria have chlorophyll and even relatively few bacteria are photosynthetic but all have cell respiration with metal-bound porphyrin rings. Even modern plants still use hemoglobins to bind and transfer  oxygen in cell respiration.

The organisms had a pathway for porphyrin or heme synthesis needing perhaps a dozen genes. The genes had variations so were subject to selection. This resulted in a new ring, the porphyrin part of chlorophyll. At the ring center was a magnesium ion instead of  an iron ion. The shift responded to the photons reaching the cell better. Chlorophyll a is activated in light and emits an electron.

Phaeophytin, a chlorophyll without Mg++  is another ring variation.

http://dipin.kent.edu/chlorophyll.htm

http://www.biologie.uni-hamburg.de/b-onl...