Naked Science Forum
Life Sciences => Cells, Microbes & Viruses => Topic started by: nudephil on 09/02/2021 18:46:46
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We received the following from listener Andrew:
I have been thinking about the origins of life in the context of random processes at the molecular biology level. The main problem seems to be the building of RNA or DNA chains of considerable length. The coronavirus has 30k bases.
With 2 to the power 2 possible bases, the coronavirus has 2 to the power 60k possible configurations - which is about ten to the power 18k. It would be expecting a lot from random processes if this level of complexity were to be achieved in one trial rather than being built up gradually by the assembly of components which were themselves built by random processes.
How might a random process build an RNA or DNA chain?
It seems to me that enzymes would play a significant role in this. Specifically there would need to be an enzyme whose purpose would be to add a base to an existing chain, thus extending it by one base unit. The choice of base unit would either be random or be determined by the enzyme itself if there was one particular base per enzyme, with four distinct enzymes.
So my question is, do these enzymes actually exist?
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there would need to be an enzyme whose purpose would be to add a base to an existing chain, thus extending it by one base unit.
So my question is, do these enzymes actually exist?
Yes, two important ones are RNA Polymerase and DNA Polymerase, and they exist in every growing and dividing cell.
- They build up RNA or DNA chains, one base at a time
See: https://en.wikipedia.org/wiki/DNA_polymerase
https://en.wikipedia.org/wiki/Transcription_(biology)
The choice of base unit would either be random or be determined by the enzyme itself..
If these enzymes selected random bases, the result would be nonsense, and would not sustain life.
- These enzymes require energy, and wasting energy on gibberish is not a good use of a cell's energy budget
In practice, the bases to be added are determined by the template in another strand of genetic material (DNA or RNA).
- The "normal" pattern in cells is DNA chain → RNA chain → Protein (also a chain)
The DNA comes from a living cell
- Sometimes the RNA comes from a virus, and hijacks the cell's protein-making factory (the Ribosome)
- Some viruses have an enzyme called "Reverse Transcriptase" which transfers RNA → DNA.
If life only comes from life (in our experience), the ultimate origin of life is the major unsolved mystery of biology.
- The enzymes processing DNA and RNA are not "pure" proteins; they usually have RNA-based components
- That has led some biologists to suggest that before cells were based on DNA, there was a form of life based on RNA.
See: https://en.wikipedia.org/wiki/Abiogenesis
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By the way, these enzymes have been in the news a fair bit over the past 9 months, as they form the basis of the most sensitive test for the SARS-COV2 virus (the virus which causes the COVID-19 disease).
This is the PCR test, or Polymerase Chain Reaction, which can multiply the tiny bit of viral RNA from a nose swab by a factor of millions or billions, so it can be detected more easily.
See: https://en.wikipedia.org/wiki/Polymerase_chain_reaction