To calculate the information and
knowledge for insulin in the last chapter, the genetic code was used to assign a
probability to each amino acid arising by chance. For this calculation to be meaningful,
both the code and a method to turn the knowledge in DNA into proteins must already exist.
So the calculations in chapter 4 assume that life already exists. What about before life
exists? How would one calculate the information or knowledge in the very first protein?
This is not an easy problem.
Several authors have used thermodynamics, but thermodynamics only
applies when the system reaches equilibrium. The relevance of thermodynamic calculations
is questionable as amino acids do not polymerize into peptides chains unless external
conditions force them away from equilibrium.
This chapter will use information theory to solve the problem. Unlike
thermodynamics, information theory can easily deal with non-equilibrium systems.
Information theory cannot normally be used to predict how chemicals
will react because some chemicals react with each other readily, and others only react
very slowly. Others do not react with each other at all. Thus, the likelihood of two
chemicals joining together depends on both the quantity of the chemicals present and their
chemical properties. Information theory can easily deal with the effects of quantity, but
it has no way to deal with chemical properties.
This chapter will require several assumptions. Without these
assumptions information theory cannot be applied to chemical reactions. Many of these
assumptions will improve the probability for creating a protein in the primordial soup.
Assumptions:
• The probability of a peptide bond forming between two amino acids
only depends on how many of each amino acid is present in the system.
• The primordial soup only contains amino acids.
• Amino acids do not form non-proteinous bonds with each other. So
for example, the carboxylic acid functional groups in aspartate and glutamate do not react
with the n-terminus of other amino acids.
The first assumption allows all amino acids to be treated equally.
While this assumption ignores the chemical properties of each amino acid, the assumption
is not an unreasonable approximation, because all amino acids must join together by
forming a peptide bond. The second assumption greatly improves the odds of creating a
functional protein. By excluding chemicals that react quickly with amino acids, this
assumption eliminates chemical reactions that can prematurely terminate a growing peptide
chain. It also ensures that the amino acids will be available to interact with each other.
The third assumption is not true, but it greatly simplifies the math, and at the same
time, it improves the odds of creating a protein in the soup.
With these assumptions, information theory may be applied to the
primordial soup. The first step is to estimate the number of each amino acid in the
primordial soup. There are two methods. For 50 years, scientists have been trying to find
better ways to synthesize amino acids under plausible prebiotic conditions. Many of the 20
amino acids used by life have been synthesized. Because these experiments are riddled with
speculation about conditions on the primitive earth and investigator interference, the
second method is preferable. This method relies on the amino acids found in meteorites.
next: Meteorites
home: Intelligent Design and the origin of Life
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