Nonoverlapping genetic code

FIGURE 27-3 Overlapping versus nonoverlapping genetic codes. In... 

THE GENETIC CODE IS DEGENERATE, UNAMBIGUOUS, NONOVERLAPPING, WITHOUT PUNCTUATION, UNIVERSAL... 

Several key properties of the genetic code were established in early genetic studies (Figs 27-3, 27-4). A codon is a triplet of nucleotides that codes for a specific amino acid. Translation occurs in such a way that these nucleotide triplets are read in a successive, nonoverlapping fashion. A specific first codon in the... 

FIGURE 27-5 Reading frames in the genetic code. In a triplet, nonoverlapping code, all mRNAs have three potential reading frames, shaded here in different colors. The triplets, and hence the amino acids specified, are different in each reading frame. 

Nonoverlapping and commaless The genetic code is nonoverlapping and commaless, that is, the code is read from a fixed starting point as a continuous sequence of bases, taken three at a time. For example, ABCDEFGHIJKL is read as ABC/DEF/GHI/JKL without any "punctuation" between the codons. 

Characteristics of the genetic code include specificity, universality, and redundancy, and it is nonoverlapping and commaless. 

The genetic code is the sequence relationship between nucleotides in the messenger RNA and amino acids in the proteins they encode. Triplet codons are arranged on the messenger in a nonoverlapping manner without spacers. 

Note the presence of chain initiation and termination codons, respectively, at the beginning and end of the sequence. In translating this sequence, which would occur within a longer mRNA molecule, into a sequence of amino acids, it has been assumed that the codons do not overlap. This has been established experimentally, and for this reason, the triplet genetic code is said to be nonoverlapping. 

The genetic code is nonoverlapping (i.e., each nudeotide is used only once), beginning with a start codon (AUG) near the 5 end of the mRNA and ending with a termination (stop) codon (UGA, UAG, or UAA) near the 3 end. 

The answer is e. (Murray, pp 452-467. Schver, pp 3-45. Sack, pp 245-257. Wilson, pp 151—180.) Chain termination is determined by three codons UAA, UAG, and UGA. Aside from chain termination codons, each group of three bases in a sequence codes for an amino acid. The next three bases specify another amino acid. Thus, the genetic code is nonoverlap-... 

The genetic code is degenerate (several codons have the same meaning), specific (each codon specifies only one amino acid), and universal (with a few exceptions each codon always specifies the same amino acid). In addition, the genetic code is nonoverlapping and without punctuation (i.e., mRNA is read as a continuous coding sequence). 

FIGURE 27-5 Reading frames in the genetic code. In a triplet, nonoverlapping code. all mRNAs have... 

FIGURE 12.2 Theoretically possible genetic codes, (a) An overlapping versus a nonoverlapping code, (b) A continuous versus a punctuated code. 

Explain what the genetic code is and list its major characteristics. Define the terms triplet code (codon), nonoverlapping, degenerate, synonym, triplet, and reading frame as they apply to the genetic code. Recognize the initiation and termination codons. 

Some of the most important features of the code can be specified by saying that the genetic message is contained in a triplet, nonoverlapping, commaless, degenerate, universal code. Each of these terms has a definite meaning that describes the way in which the code is translated. 

Genetic information, that is, instructions for protein synthesis, is carried in the deoxyribonucleic acids. Each sequence of three bases is a triplet code or codon, which controls the incorporation of specific amino acid into a growing protein chain or is a signal for the synthesis to terminate (see Section 30.3.1). The triplet code is a nonoverlapping type of code. 

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