The answer to that question depends on how we define life or living. Life is itself is so complex, or maybe so elusive, that we have no adequate definition for it. In order to adequately define life, we must first understand what life is. Some scientists are working to produce a cell with a minimum amount of genetic information, and believe they may be able to produce what we mean by a "living cell." Until that is accomplished (if it is indeed even possible), we will not have a complete definition of "life."
However, we can partially define a living cell by ascribing to it some of the properties that all living systems display. Some who believe in the possibility for the spontaneous origin of life attempt to simplify the definition life to the point that it has no resolving power whatsoever. Anything is considered alive, including a simple sphere made of polymerized amino acids! They do this in order to foster the vain hope that such a product could somehow account for the complexity and information content of a living cell.
Being realistic, we can include a generalized list of things that would have to go on in such a cell for it to be considered alive. If a living cell is defined as an integral structure that carries on metabolic processes and is capable of independent replication, then we may or may not have a structure that is alive, but at least we can formulate an answer to the question you have posed.
For metabolism to be functional, the cell has to take in an energy source (or be photosynthetic), use that energy source to make necessary biomolecules, then assemble these biomolecules into complex, information-rich polymers such as enzymes (proteins that regulate the rate and extent of specific chemical reactions in the cell), structural proteins and nucleic acids (DNA and RNA) that comprise the mechanisms and pathways of the cell. Already we are faced with a formidible dilemma. In order to make the polymers (enzymes) needed to make the monomers, we have to first have mechanisms in place that are made of polymers (enzymes, ribosomes and DNA-RNA), in all living cells.
Where did these polymers come from?
One could postulate that some of the monomers were obtained from the environment initially. But that doesn't solve the dilemma. We still cannot make the polymers without polymers being present. And the only route to information-rich polymers we know is through other polymers.
Consider the genetic code. Suppose that you had produced by accident a stretch of DNA template that just happened to code for a protein important for some needed function. Now what? You can't get from DNA to protein without having a mechanism that can read the code in the DNA and translate that code into a sequence of amino acids in the specified protein.
There is no physical or chemical relationship between the sequence of bases in a DNA codon and the amino acid specified by the genetic code. In order for the code to be read, an adaptor molecule must be present for each of the amino acid/codon pairs. This adaptor molecule, a small (120 bases or so) molecule of RNA, called transfer RNA or t-RNA must recognize the three base code of the DNA-RNA (theoretically, either DNA or RNA could be read in a primitive cell. In all living cells, only the RNA is read in making proteins. The RNA is made from a DNA template). It must also somehow become associated with a specific amino acid that corresponds to that codon, so that the amino acid is attached to the t-RNA. But such a sophisticated process must itself be carried out by a protein, in living cells, an enzyme that specifically recognizes the correct amino acid and the correct t-RNA, and joins them together. These enzymes, called amino acyl t-RNA synthetases are one reason why evolution of a living cell is just not possible. Each of the 20 or so t-RNA synthase enzymes in living cells functions with one specific t-RNA or set of t-RNAs and one specific amino acid. Without a set of 20 or so of these enzymes, we can have all of the DNA-RNA templates for specific proteins in the world, and we will not get a single protein produced.
When we examine the sequences of these 20 enzymes, although they all do essentially the same thing (attach a specific amino acid to a specific tRNA) there is virtually no similarity in the amino acid sequences between the different enzymes. While in some cases, the enzyme for a particular amino acid may show homology across species, enzymes for different amino acids have essentially no homology with one another. The molecular weight range for the enzymes ranges from 60 kD to more than 200 kD. While evolutionists can do phylogenetic trees for an individual enzyme, it is impossible to generate evolutionary relationships for the origin of all of the enzymes. Each enzyme appears to have been individually crafted for its job. The bottom line is: without these enzymes and the protein synthesizing apparatus of all cells (the ribosome) there can be no protein. Without protein, there can be no life.
Some have speculated that a RNA world may have preexisted the DNA/protein world of today. Such speculation is amusing, because it reveals how little confidence origin of life researchers have in the liklihood of origin of a prebiogenic living cell, it is also without a shred of support. RNA is far more labile than DNA, it is more difficult to make, and the aspirations of abiogenically-generated functional "ribozymes" (RNA with enzymatic functions) to carry out any of the requisite reactions of self-replicating life have never been realized. There is not even a realistic hypothesis to explain how this could come about abiogenically. ______________________________________________________
2010 Arthur V. Chadwick, Ph.D.