Composition, protein identity based

Prediction of protein identity based on composition AACompIdent http //www. expasy. ch/tools/aacomp/... 

The peptides, which are composed of only a few amino acids, exhibit predictable behavior in CZE in that their mobility (electrophoretic migration) can be predicted on the basis of their size (mass) and their charge characteristics. The charge of such peptides can be predicted from the pKa values of individual amino acids contained in them. For larger peptides and proteins, the calculation of charge based on ionization constant is not trivial and can not be easily calculated based on the pKas of the free amino aids. Besides the mass-to-charge ratio, the other factors that affect mobility are hydrophobic-ity, primary sequence, conformational difference, and the chirality of amino acids. This point has been demonstrated by an investigation on several nonapeptides of identical composition but with different primary sequences ... 

Class I elements (Figure 25.35) encode a transposase but not a resolvase, and are of two types. The simplest is called an insertion sequence (IS), which consists simply of a gene for transposase, flanked by two short inverted repeat sequences of about 15 to 25 base pairs. A less simple structure, called a composite transposon, consists of a protein-encoding gene, such as a gene conferring antibiotic resistance, flanked by two insertion sequences, or IS-like elements. These elements may be in either identical or inverted orientations. 

Morphologists postulated for many years that the transfer of information from DNA to protein involves a form of nuclear RNA that migrates from nucleus to cytoplasm. This hypothesis found some concrete support as molecular biology developed. At first, it was found that a small fraction of bacterial RNA has a base composition identical to DNA in bacteria infected with T phage. The synthesis of DNA-depend-ent RNA was demonstrated in bacterial preparations and in mammalian nuclei. Triphosphate ribosides (UTP, GTP, CTP, and ATP) are required precursors for the synthesis of the new polynucleotide. Double-stranded DNA serves as a template in the reaction, and an RNA polymerase catalyzing the polymerization of the ribonucleotide was partially purified from both the bacterial and mammalian systems. 

Infant Formulas. A wide variety of infant formulas are marketed that all attempt to approximate the composition of breast milk. Some are based on soy or other proteins for inhmts who are lactose intolerant or aUei ic to milk products. None of the products are identical to breast milk, which is a species-specific formulation for human babies. Each animal species has a unique milk formulation for its young. Also, breast milk can supply maternal antibodies, which can protect the infimt from infection. For the foregoing reasons and others, many women choose to breast-feed. Some of these women will rely on breast pumps for regular or occasional use. 

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