What are the minimum requirements for a cell to live? A minimal free-living cell that can manufacture its components using chemicals and energy obtained from its surrounding environment and reproduce itself must have: A cell membrane. This separates the cell from the environment. It must be capable of maintaining a different chemical environment inside the cell compared to outside (as above). Without this, life’s chemical processes are not possible. A way of storing the information or specifications that instructs a cell how to make another cell and how to operate moment by moment. The only known means of doing this is DNA and any proposals for it to be something else (such as RNA) have not been shown to be viable—and then there has still to be a way of changing from the other system to DNA, which is the basis of all known life.15 A way of reading the information in (2) to make the cell’s components and also control the amount produced and the timing of production. The major components are proteins, which are strings (polymers) of hundreds to thousands of some 20 different amino acids. The only known (or even conceivable) way of making the cell’s proteins from the DNA specifications involves over 100 proteins and other complex co-factors. Involved are nano-machines such as RNA polymerase (smallest known type has ~4,500 amino acids), gyrases, which twist/untwist the DNA spiral to enable it to be ‘read’ (again these are very large proteins), ribosomes, sub-cellular ‘factories’ where proteins are manufactured, and at least 20 transfer-RNA molecules; these select the right amino acid to be placed in the order specified on the DNA (all cells that we know of have at least 61 because most amino acids are specified by more than one DNA three-letter code). The transfer-RNAs have sophisticated mechanisms for making sure the right amino acid is selected according to the DNA code. There are also mechanisms to make sure that the proteins made are folded three-dimensionally in the correct way that involve chaperones to protect the proteins from mis-folding, plus chaperonin folding ‘machines’ in which the proteins are helped to fold correctly). All cells have these. Whew! And that’s just the basics creation/origin-of-life
Posted on: Mon, 31 Mar 2014 16:33:09 +0000
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