Polynucleotide chain length

The first replicative units must have possessed considerably less information than the RNA viruses, which work with an optimized RNA-copying machinery. In the absence of efficiently adapted enzymes the accuracy of reproduction depends solely on the stability of the base pairs. Under these conditions the GC pair has a selective advantage over the AU pair of a factor of about 10. Model experiments show that for GC-rich polynucleotides the error rate per nucleotide can hardly be reduced below a value of 10-2. The first genes must accordingly have been polynucleotides with a chain length around 100 bases or less. 

Figure 7. Structure of segmented polynucleotide sequences. Sequence is built from two segments of chain lengths and Vg, respectively n different sequences can be formfed by combination of r segments of type A and s segments of type B.

In general, chain lengths v are not conserved in polynucleotide replication. Insertions and deletions are common. Duplications of longer parts of sequences occur as well. Every polynucleotide thus has to compete not only with molecules of the same chain length but also with longer and shorter sequences. 

The factor fg is an appropriate measure of the fitness of polynucleotides that carry unused or redundant parts and compete with shorter and longer sequences. In case the rate of replication does not depend on the chain length, fg will be close to 1 and longer sequences may compete successfully with shorter ones. Rates of replication that are largely insensitive to chain lengths are particularly important for the process of gene duplication. A coding... 

Figure 30. Error threshold as function of population size. Stochastic replication-mutation dynamics in ensemble of polynucleotide sequences with chain length v = 20 simulated by Gillespie s algorithm [95]. Critical single-digit accuracy of replication (q in) at which ordered quasi-species is converted into changing population of sequences with finite lifetimes is plotted as function of 1/N, reciprocal population size (lower curve). For further details see ref. 96. Upper curve is theoretical prediction of Eqn. (V.l) based on ref. 51.

Polynucleotides. Aryl phosphorodichloridates (1,847) are useful for synthesis of short oligonucleotides by the phosphotriester procedure however, the reactions are slow and yields are low as the chain length is increased. However, aryl phosphorodichloridites react with hydroxyl groups in THF at -78°... 

Simha, R., Zimmerman, J. M., Calculation of chain length distribution between markers in mixed polynucleotides. Journal of Theoretical Biology, 8(1), pp. 81-86 (1965). 

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