CAG codon

Another possible application of suppressor genes is in vivo suppression of undesirable termination codons. An example comes from a p° thalassemia caused by mutation of lysine codon CAG to UAG. By changing the anticodon of a human tRNALys gene to... 

The next step in the description of the DNA sequence is the analysis of the pair-wise nearest-neighbor correlations Cy, for example, the normalized probabilities to And successive pairs of the nucleotides i and j. Eor all 16 possible successive dinucleotides in the coding strand of DNA, only the functions Cag and CcT correlate with OGT. The excess probabilities to find ApG and CpT pairs in the coding DNA are increasing significantly with OGT, correlation coefficient R = 0.68 and 0.601 (Fig. 2, upper row). Remarkably, the codon bias explains the observed sequence correlations in the coding parts of DNA. Eirst,... 

Elongation. The next aminoacyl-tRNA (in Fig. 70.1 it is glycinyl-tRNA ) binds to the A site attracted by the next codon (CAG) of the mRNA. NB Initiator methionyl-tRNAi (the special one ) binds to the ribosomal P site whereas all other aminoacyl tRNAs bind to the... 

Amber codon, nonsense codon the sequence UAG in mRNA. It does not code for any of the 20 proteogenic amino acids, and it results in the termination of protein synthesis (premature termination when UAG is produced by mutation of a sense codon). Potential precursors for the production of UAG by mutation are UCG (serine), UAU and UAC (tyrosine) and CAG (glutamine). 

A sequence of three bases in mRNA, called triplets, or codons, code for specific amino acids. Thus, the sequence CAG codes for glutamic acid, and GUC codes for valine. There are 64 (4 ) unique combinations of three-base sequences made from four bases. Some amino acids have more than one code. For example, leucine is coded for by six different codons UUA, UUG, CUU, CUC, CUA, and CUG. Methionine and tryptophan are the only amino acids that are coded by only one codon each. The same three-base sequence always codes for the same amino acid regardless of whether the organism is a bacterium or a human. 

A protein is biosynthesized from its N-terminal end to its C-terminal end by a process that reads the bases along the mRNA strand in the 5 3 direction. The amino acid that is to be incorporated into a protein is specified by a three-base sequence called a codon. The bases are read consecutively and are never skipped. The three-base sequences and the amino acid that each sequence codes for are known as the genetic code (Table 26.2). A codon is written with the 5 -nucleotide on the left. For example, the codon UCA on mRNA codes for the amino acid serine, whereas CAG codes for glutamine. 

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