Nucleotide sequences information content

Information content, (a) How many different 8-mer sequences of DNA are there (Hint There are 16 possible dinucleotides and 64 possible trinucleotides.) We can quantify the infonnation-carrying capacity of nucleic acids in the following way. Each position can be one of four bases, corresponding to two bits of information (2 = 4). Thus, a chain of 5100 nucleotides corresponds to 2 X 5100 = 10,200 bits, or 1275 bytes (1 byte = 8 bits), (b) How many bits of information are stored in an 8-mer DNA sequence In the E. coli genome In the human genome (c) Compare each of these values with the amount of information that can be stored on a computer compact disc (CD). 

The DNA base pairs described earlier in this chapter are linked together in long chains. There are four nucleotide bases linked together in extremely long chains, coiled up and bound with proteins to form chromosomes. The information content of DNA is mainly contained in the order of these base pairs, the DNA sequence. DNA is the structure by which individual traits are transmitted from generation to generation. The linear code of four letters is analogous in some ways to the linear code of O s and l s in computer software, which also instruct hardware to carry out functions and can be copied faithfully for transmission. 

Proteins have 20 building blocks (amino acids) and DNA has only four (nucleotides), yet the messages in the two sequences have the same information content and are translatable. Could there be an informational molecule with even fewer than four building blocks ... 

A full release of GenBank occins on a bimonthly schedule with incremental (and nonincremental) daily updates available by anonymous FTP. The International Nucleotide Sequence Database Collaboration also exchanges new and updated records daily. Therefore, all sequences present in GenBank are also present in DDBJ and EMBL, as described in the introduction to this chapter. The three databases rely on a common data format for information described in the feature table documentation (see below). This represents the lingua franca for nucleotide sequence database annotations. Together, the nucleotide sequence databases have developed defined submission procedures (see Chapter 4), a series of guidelines for the content and format of all records. 

According to their theory, as the polycistronic messenger RNA moves in relation to the polysome system, the velocity of protein synthesis in its various parts is slowed. They postulated that the sequence of the genes in the histidine operon (which does not correspond to the biochemical sequence of reactions) is connected with the number of molecules of each enzyme synthesized. By analyzing the frequency of mutations of polarity, they concluded that many triplets (of the 64 possible) can retard the transcription and translation of information. The essence of the matter is that if any nucleotide triplet (codon) XYZ requires an anticodon in the molecules of acceptor sRNA for itstranslationinto a protein "text," a lowered content of this fraction of sRNA with the corresponding anticodon may act as modulator of the velocity of translation, which is reduced at this locus in connection with a decrease in the number of codon-anticodon interactions. 

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