Signal sequences representative, table

An alternative method to the J-B sequence is the selective inversion (SI) technique [2.21]. Both the J-B and SI methods give the same efficiency in measuring Tig, but the SI method is inferior in determing T z because of a decrease of a factor of 2 in the signal-to-noise ratio. It is noted that because of Eq. (2.77), a separate experiment is required for each distinct quadrupole doublet. Alternatively, broadband excitation may be used to irradiate several doublets identically using a composite J-B sequence [2.22, 2.23]. Recently, this broadband J-B excitation sequence was used to create quadrupolar orders with same efficiency on all the labeled sites in a liquid crystal [2.24]. This is particularly useful if the NMR spectrum represents a powder sample. The modification of the J-B sequence (Table 2.3) to produce a broadband excitation sequence is shown in Table 2.4. This has been used to minimize the number of separate experiments required to give Tiz and Tig for various deuterons in several deuterated nematogens [2.25]. 

The information contained in the base sequence of the mRNA template is interpreted in sequences of three bases called codons each codon represents one amino acid. Therefore, the unit of information is the codon. Since there are four major bases in mRNA, 4 (i.e. 64) different codons are possible. The 64 triplets constitute the genetic code (Table 17.1). All codons have been assigned to amino acids or punctuation signals. Three triplets (UAA, UAG and UGA) are not complemented by anticodons on tRNAs and serve to signal that the polypeptide chain has been completed. Of the other 61 triplets which have complementary tRNAs, two (AUG and GUG) have additional roles in the initiation of protein synthesis. Since there are only 20 amino acids, most amino acids are specified by more than one codon, i.e. the code is degenerate. The genetic code applies to prokaryotes and eukaryotic nuclear and chloroplast mRNAs but not to... 

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