Nucleotides in mRNA

Codon (Section 28.11) Set of three successive nucleotides in mRNA that is unique for a particular amino acid. The 64 codons possible from combinations of A, T, G, and C code for the 20 amino acids from which proteins are constructed. 

Twenty different amino acids are required for the synthesis of the cellular complement of proteins thus, there must be at least 20 distinct codons that make up the genetic code. Since there are only four different nucleotides in mRNA, each codon must consist of more than a single purine or pyrimidine nucleotide. Codons consisting of two nucleotides each could provide for only 16 (4 ) specific codons, whereas codons of three nucleotides could provide 64 4 ) specific codons. 

CODON Three contiguous nucleotides in mRNA that specify the amino acid to be inserted at a specific position in a polypeptide during translation of the 64 possible codons that are formed by the four types of nucleotides in SNA (nucleotides of adenine, guanine, cytosine, and uracil), 61 specify an amino acid and three (nonsense codons) specify no amino acid, but rather serve as termination signals in protein synthesis. 

The sequence of nucleotides in mRNA is converted through the translation machinery into a sequence of amino acids that constitutes a polypeptide. This machinery includes tRNA and ribosomes (which contain rRNA and a collection of unique proteins). The function of tRNA is to act as an adapter between the nucleotide sequence (defining the order of codons) and the amino acid sequence to be assembled into a polypeptide. 

C4 metabolism a photosynthetic pathway that produces a four-carbon molecule and avoids photorespiration in eukaryotic photo-synthesizing organisms coding strand the DNA strand that has the same base sequence as the RNA transcript (with thymine instead of uracil) codon a sequence of three nucleotides in mRNA that directs the incorporation of an amino acid during protein synthesis or acts as a start or stop signal coenzyme a small organic molecule required in the catalytic mechanisms of certain enzymes... 

Codon Three consecutive nucleotides in mRNA that specify a given amino acid during protein synthesis the anticodon of tRNA is complementary to the mRNA codon. 

A codon is a triplet of adjacent nucleotides in mRNA that specifies an amino acid to be incorporated in a protein. Because the codon can be made from three of the four possible ribonucleotides, there are 4 or 64 combinations, leading... 

Translation relies on the genetic code, in which three nucleotides in mRNA specify one amino acid in protein. 

A transfer RNA has one binding site for a specific sequence of three nucleotides in mRNA (the anticodon site) and another binding site for the encoded amino acid. tRNAs thus ensure that the genetic code is translated into the correct sequence of... 

What is the minimum number of contiguous nucleotides in mRNA that can serve as a codon Explain. 

Three contiguous nucleotides is the minimum that can serve as a codon. There are four kinds of nucleotides in mRNA. A codon consisting of only two nucleotides (either of which could be any of the four possible nucleotides) allows only 16 possible combinations (4 x 4 = 16). This would not be sufficient to specify all 20 of the amino acids. A codon consisting of three nucleotides, however, allows 64 possible combinations (4x4x4 = 64), more than enough to specify the 20 amino acids. 

Initiation codon, start codon a sequence of three nucleotides in mRNA which is recognized by the anticodon of formylmethionyl-tRNA (prokaryotes) or methionyl-tRNA (eukaryotes) and thus serves as the start signal for polypeptide synthesis The I. c. has the sequence S -AUG and is apparently localized in a sterically favorable position of the mRNA. See Genetic code. 

Termination codon, stop codon, punctuation codon a sequence of three nucleotides in mRNA, which signals the end of polypeptide synthesis and release of the polypeptide in the process of Protein biosynthesis (see). 5 -tlAA (see Ochre codon), 5 -UAG (see Amber codon) and UGA are T.c. 

Transcription proceeds in the 3 -to-5 direction along the DNA template. That is, the mRNA chain grows from its own 5 end. The 5 terminal nucleotide in mRNA is usually present as a triphosphate, not a monophosphate, and is commonly pppG or pppA. An enzyme called RNA-polymerase is essential for transcription. Usually only one strand of DNA is transcribed. It contains base sequences, called promoter s/fes, which initiate transcription. It also contains certain termination sequences, which signal the completion of transcription. 

Reading frame One of three possible ways of translating groups of three nucleotides in mRNA. The appropriate reading frame is determined by the initiation codon. 

Indicate the nucleotides in mRNA that code for the following ... 

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