Aspartate codons

X can be any of the four nucleobases—G, A, C or U thus, four anticodons can be formed GGC, GAC, GCC and GUC. The antiparallel structure contains the codons GCC, GUC, GGC and GAC. Today, these codons code for the four amino acids alanine, glycine, valine and aspartic acid. These are, astonishingly, the four protein building blocks produced in the best yields in the Miller-Urey experiment, and they... 

Figure 5.8 An hypothetical genetic code in which aspartic acid and glutamic acid are coded for by twice the number of codons that exist in the natural code, thus producing a world of more acidic proteins.

A study of Colorectal adenomas and cancers in human patients revealed sei eral types of mutations occurring in RAS. The mtwt common mutations affected codon 12, which consists of GGT, and codes for the I2th amino acid of the polypeptide. Most of these mutations resulted in the conversion of GGT, which codes for glycine, to GAT (aspartate), to GTT (valine), and to GCT (alanine) (Zhu ef ai, 1997). The mutations t ccurred at the central base of codon 12 and can be summarized as ... 

One kind of RNA—called, fittingly, messenger RNA—carries a message to the ribosome, where protein synthesis actually takes place. At the ribosome, messenger RNA calls up a series of transport RNA molecules, each of which is loaded with a particular amino acid. The order in which the transport RNA molecules are called up—the sequence in which the amino acids are built into the protein chain—depends upon the sequence of bases along the messenger RNA chain. Thus, GAU is the code for aspartic acid UUU, phenylalanine GUG, valine. There are 64 three-letter code words codons) and only 20-odd amino acids, so that more than one codon can call up the same amino acids CUU and CUC, leucine GXA and GAG, glutamic acid. 

It follows that the array of codons represents the instructions for producing 20 amino acids, the so-called common amino acids. These amino acids are named and symbolized as alanine (Ala), arginine (Arg), asparagine (Asn), aspartate (Asp), cysteine (Cys), glutamine (Gin), glutamate (Glu), glycine (Gly), histamine (His), isoleucine (lie), leucine (Leu), lysine (Lys), methionine (Met), phenylalanine (Phe), proline (Pro), serine (Ser), threonine (Thr), tryptophan (Trp), tyrosine (Tyr), and valine (Val). 

Fig. 2. A portion of the tandem mass spectrum of the glycopeptide, residues 195-204, containing the second glycosylation site, after treatment with PNGase E The mass difference of 115 Da between the b2 and bs ions is attributable to aspartic acid as the third residue (codon 197) rather than asparagine. (Reproduced with permission from Baldwin, MA. et al. [1993]. Trends in Analytical Chemistry 12, 239-248. Copyright Elsevier Science.)...

Viral replication in the presence of nelfinavir selects for drug resistance. The primary nelfinavir resistance mutation is unique to this drug and occurs at HIV protease codon 30 (aspartic acid-to-asparagine substitution) this mutation results in a sevenfold decrease in susceptibility. Isolates with only this mutation retain full sensitivity to other HIV protease inhibitors. Less conunonly, a primary resistance mutation occurs at position 90, which can confer crossresistance. In addition, secondary resistance mutations can accumulate at codons 35, 36, 46, 71, 77, 88, and 90, and these are associated with further resistance to nelfinavir, as well as cross-resistance to other HIV protease inhibitors. 

Hemoglobin Swan River differs in having GGC instead of GAC as the sixth codon. The corresponding amino changes from aspartic acid to glycine. 

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