Electron Transport Chain

Question

Question: Speculate on the role evolution may have played in the existence of these two different electron transport chains. Support your ideas referencing the common mechanisms of evolution and the similarities and differences in the ETC in mitochondria and chloroplasts.

Answer 1

Khloe:

The way to go about answering this question is first to think about what each of the ETC are doing. In both cases, energetic or 'high value' electrons are at the beginning (in photosynthesis, they are energized by a photon of light; in respiration, they are taken from bonds in which electrons are relatively energetic such as C-C or C-H bonds). If you look closely, you'll see that many of the steps involve similar or identical components. If you look less closely, you'll see that overall, the exact same things are happening: energy is taken from the electrons as the do the work of moving protons 'up' a concentration gradient (i.e. to a place of HIGHER proton concentration). In both cases, the protons then 'power' a machine that forces a phosphate onto ADP, creating portable, handy ATP.

 

These similarities should suggest your thinking on evolution. It is always easier (= more likely) to duplicate/copy an existing machine/mechanism than to discover something by chance. So it is incredibly likely that the two look alike and share common elements not just because they achieve similar ends, but because one began from the other.

 

Here's a great cartoon overviewing the two processes

https://www.ncbi.nlm.nih.gov/books/NBK21063/figure/A2494/?report=objectonly