Intelligent Design, the best explanation of Origins

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Intelligent Design, the best explanation of Origins » Origin of life » What are the minimum requirements for a cell to live?

What are the minimum requirements for a cell to live?

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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.

A greatly simplified animation of protein synthesis, which includes the action of RNA polymerase, ribosomes, transfer-RNAs, chaperonins, and chaperones. All living cells have this system of protein synthesis.
A means of manufacturing the cell’s biochemical needs from the simpler chemicals in the environment. This includes a way of making ATP, the universal energy currency of life. All living cells today have ATP synthase, a phenomenally complex and efficient electric rotary motor to make ATP (or in reverse to create electric currents that drive other reactions and movement both inside and outside the cell).

A means of copying the information and passing it on to offspring (reproduction). A recent simulation of one cell division of the simplest known free-living bacterium (which ‘only’ has 525 genes) required 128 desktop computers working together for 10 hours.16

This gives some indication of what needs to happen for the first living cell to live.

An interesting project began some years ago to ascertain what could be the minimal cell that could operate in a free-living manner; that is, not dependent on another living organism. However, it did have available a nutrient-rich medium that provided a wealth of complex organic compounds such that the cell did not have to synthesize many of its needed biochemicals. This minimal cell is now known to need over 400 protein and RNA components,17 and of course that means that its DNA needs to be loaded up with the specifications for making these. That is, the DNA needs to have over 400 ‘genes’. We will come back to this later.

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Leaving aside the technical problems of such chemistry, what would a primordial cell need to survive, replicate, and to get the evolutionary ball rolling? First, a method for capturing energy (e.g.: photosynthetic organisms that make their own food) or a mechanism for utilizing energy derived from pre-formed organic molecules. Both methods involve very complex biochemistry even in the simplest of organisms. Second, a membrane to keep the outside environment separate from the metabolic reactions within the cell. Third, a system by which genetic information can be stored and accessed (DNA). Fourth, a mechanism to convert this information into the molecular tools the cell requires to function. Finally, the all-important requirement for cellular division and self-replication. The stored genetic information must be replicated and passed onto daughter cells in order to produce descendant life forms.

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