Question

Assume that you are employed as a developmental biologist at NASA and the first returning mars explorer was found to have a small organism from mars onboard. The organism had the usual head-tail axis as well as dorsal-ventral polarity and what appeared to have right-left asymmetry. However upon analysis it was found to be composed of silicon based compounds and had no DNA, RNA or proteins at all. Discuss reasons why this organism would have similar developmental controls to those of earth’s carbon-based life and also discuss the opposing view as to why it would not. YOU MUST PROVIDE AS MICH DETAIL AS POSSIBLE IN ORDER TO RECEIVE FULL CREDIT.

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Answer 1

Silicon is the second most abundant element on earth but yet all the life forms are based on carbon. Carbon and silicon have four chemical bonds and thus are chemically similar in structure. They both can bind to oxygen and form long chains, called polymers. Carbon forms poly-acetal polymer while silicon forms polymeric silicones. Based on these facts one can say that silicon can also form a bases of life as that of carbon but it is not practically feasible. The possible reasons why silicon could not be adopted as the way carbon is adopted are –

a)         Silicon reacts much slowly as compared to carbon

b)         The bond between Si-Si and Si-H are not stable as C-H and C-C bonds

c)         In ability to form double or triple bonds by pi bonds or sigma bonds at normal temperature and pressure

d)         Silicon oxidizes to solid and hence cannot support life

e)         Handedness is essential to form variety of biomolecules to recognize and regulate biological processes which is not possible in case of silicon as it doesn't form many compounds having handedness

Silicon organisms with environmental conditions like Earth cannot be found in stars. Also the compounds composed mainly of silicon are far fewer than those of carbon. If there is some life in stars other than earth, it is natural to assume that extraterrestrial life forms are carbon organisms and not silicon organisms.