Nucleotide pair, frequency

What is the scientific value of analyzing the frequency of ocourence of the various nucleotide pairs What information is yielded by this that a knowledge of the base composition does not provide ... 

Restriction enzymes that recognize a specific sequence of five nucleotides should cut the DNA, on average, every 45 base pairs (this is the frequency with which a given sequence of five nucleotides would occur by chance), or every 1024 base pairs. As a result, the average size... 

Biezo, G, J. Ladik, and J. Gergely Approximate calculation of the tunnelling frequencies of the proton in the N-H---0 hydrogen bond of the nucleotide base pairs. Physics Letters 13, 317 (1964). 

This enzyme has a proofreading role. At a low random frequency, incorrect bases (in the form of nucleotides) are inserted into the growing DNA chain. This results from the existence of rare tautomeric forms of the four bases, which, if occurring transiently in the template at the moment of insertion of an incoming nucleotide, will cause a mistake in base pairing. When such a template nucleotide shifts back to its preponderant form, a base pair mismatch results. The 3 —>5 exonuclease recognizes the mismatch and catalyzes the hydrolytic removal of the nucleotide from the end of the chain before elongation resumes. 

Most mutations represent the replacement of one base by another a minority is caused by deletions of some base pairs, by frameshift, by polypeptide chain elongation due to mutation of a terminator codon, or by recombinational events with mutation-like effects. The replacement of one base for another is currently indicated by the term single-nucleotide polymorphism, abbreviated as SNP. It occurs at a frequency of roughly one per every 500-1000 base pairs of genomic DNA, which means that most genes carry one or two SNPs, although many are without any functional significance. ... 

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