Nucleic acid sequencing translation

Molecular biology involves the study of the major macromolecules, DNA, RNA, and protein. The central dogma ofmolecular biology is illustrated in Fig. 2. The central dogma shows the relationship among the macromolecules in the processes of transcription and translation. Figure 2 also gives the relationship between immunoelectron microscopy and in situ hybridization. In situ hybridization allows one to localize a specific nucleic acid sequence. Immunoelectron microscopy is an essential component to the technique of in situ hybridization when applied at the EM level. 

It is only natural that, to date, bioinformatics tools contribute most to the analysis of amino acid sequences. Only a small amount of current sequence data is subjected to direct experimentation. The majority of amino acid sequences currently accessible in public databases have been derived by in silico translations of nucleic acid sequence data, despite the fact that amino acid sequencing was introduced historically long before nucleic acid sequencing. It is hard to predict the future of the experimental generation of primary data. Certainly, sequencing of nucleic acids continues to become cheaper and faster, and novel techniques may further enhance the production of data. DNA chips are already used to detect differences between very similar sequences other methods may generate DNA data even more efficiently. 

Human apoA-I is a major constituent of HDL, with an Mr of approximately 28,300, calculated from the known primary structure (Bl, B43). ApoA-I is initially synthesized as a 267-amino-acid precursor protein, pre-pro-apoA-I (G25, G26), containing an 18-amino-acid prepeptide and a 6-amino-acid propeptide [determined by nucleic acid sequence analysis of cloned apoA-I (L6), and by isolating the primary translation product of human intestinal apoA-I mRNA (G25)]. 

Another difference between prokaryotic and eukaryotic translation is the nucleic acid sequences that recruit the small ribosomal subunit to the mRNA. As stated earlier, the Shine-Delgarno sequence interacts with the 16S rRNA of the 3 OS ribosomal subunit in the prokaryotic system, the critical step in translation initiation. In the eukaryotic... 

RNA has three basic roles in the cell. First, it serves as the intermediate in the flow of information from DNA to protein, the primary functional molecules of the cell. The DNA is copied, or transcribed, into messenger RNA (mRNA), and the mRNA is translated into protein. Second, RNA molecules serve as adaptors that translate the information in the nucleic acid sequence of mRNA into information designating the sequence of constituents that make up a protein. Finally, RNA molecules are important functional components of the molecular machinery, called ribosomes, that carries out the translation process. As will be discussed in Chapter 2, the unique position of RNA between the storage of genetic information in DNA and the functional expression of this information as protein as well as its potential to combine genetic and catalytic capabilities are indications that RNA played an important role in the evolution of life. 

Protein synthesis is called translation because information present as a nucleic acid sequence is translated into a different language, the sequence of amino acids in a protein. This complex process is mediated by the coordinated interplay of more than a hundred macromolecules, including mRNA, rRNAs, tRNAs, aminoacyl-tRNA synthetases, and protein factors. Given that proteins typically comprise from 100 to 1000 amino acids, the frequency at vchich an incorrect amino acid is incorporated in the course of protein synthesis must be less than 10 4. Transfer RNAs are the adaptors that make the link betvceen a nucleic acid and an amino acid. These molecules, single chains of about 80 nucleotides, have an L-shaped structure. 

FIGURE 12.44. Descriptors of base and base-pair (bp) orientations. Shown at the top (a) are idealized beise-pair arrangements viewed down the helix axis z). Perturbations are illustrated for (b) rotation of one base pair, (c) rotation of two base pairs adjacent in the nucleic-acid sequence, (d) translation for one base pair, and (e) translation for two base pairs adjacent in the nucleic-acid sequence. 

Synthetic peptides can serve as antigens to stimulate the formation of specific antibodies. Suppose we want to isolate the protein expressed by a specific gene. Peptides can be synthesized that match the translation of part of the gene s nucleic acid sequence, and antibodies can be generated that target these peptides. These antibodies can then be used to isolate the intact protein or localize it within the cell. 

This flow of information depends on the genetic code, which defines the relation between the sequence of bases in DNA (or its mRNA transcript) and the sequence of amino acids in a protein. The code is nearly the same in all organisms a sequence of three bases, called a codon, specifies an amino acid. There is another step, between transcription and translation, in the expression of most eukaryotic genes, which are mosaics of nucleic acid sequences called introns and exons. Both are transcribed, but introns are cut out of newly synthesized RNA molecules, leaving mature RNA molecules with continuous exons. The existence of introns and exons has crucial Implications for the evolution of proteins. 

Protein synthesis is called Lranslalioii because information present as a nucleic acid sequence is translated into a different language, the sequence of amino acids in a protein. This complex process is mediated by the coordinated interplay of inore than a hundred macro molecules, including mRNA, rRNAs, tRNAs, aminoacyl-tRNA synthetases,... 

Translate nucleic acid sequence into protein and vice versa... 

Protein synthesis is an extraordinarily complex process in which genetic information encoded in the nucleic acids is translated into the 20 amino acid alphabet of polypeptides. In addition to translation (the mechanism by which a nucleotide base sequence directs the polymerization of amino acids), protein synthesis can also be considered to include the processes of posttranslational modification and targeting. Posttranslational modification consists of chemical alterations cells use to prepare polypeptides for their functional roles. Several modifications assist in targeting, which directs newly synthesized molecules to a specific intracellular or extracellular location. 

A FIGURE 4-21 Two-step decoding process for translating nucleic acid sequences in mRNA into amino acid sequences in proteins. StepD An aminoacyl-tRNA synthetase first couples a specific amino acid, via a high-energy ester bond (yellow), to either the 2 or 3 hydroxyl of the terminal adenosine in the... 

Translation, therefore, is the conversion of the information in the nucleic acid sequence to polypeptides of a specific amino acid sequence. The process of translation requires a system to bring the mRNA together with the translating molecules (tRNAs). The system must also catalyze the polymerization of the amino acids into a polypeptide sequence. 

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