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Transcription - message is received The nucleotides of the...

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Transcription Transcription  is one of the first processes in the mechanism of protein synthesis. In  transcription, a complementary strand of mRNA is synthesized according to the  nitrogenous base code of DNA. To begin, the enzyme RNA polymerase binds to an area  of one of the DNA molecules in the double helix. (During transcription, only one DNA  strand serves as a template for RNA synthesis. The other DNA strand remains  dormant.) The enzyme moves along the DNA strand and “reads” the nucleotides one by  one. Similar to the process of DNA replication, the new nucleic acid strand elongates in  a 5 -3  direction, as shown in Figure  1  . The enzyme selects complementary bases from  available nucleotides and positions them in an mRNA molecule according to the  principle of complementary base pairing. The chain of mRNA lengthens until a “stop” 
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Unformatted text preview: message is received. The nucleotides of the DNA strands are read in groups of three. Each group is a codon . Thus, a codon may be CGA, or TTA, or GCT, or any other combination of the four bases, depending on their sequence in the DNA strand. Each codon will later serve as a “code word” for an amino acid. First, however, the codons are transcribed to the mRNA molecule. Thus, the mRNA molecule consists of nothing more than a series of codons received from the genetic message in the DNA. After the “stop” codon is reached, the synthesis of the mRNA comes to an end. The mRNA molecule leaves the DNA molecule, and the DNA molecule rewinds to form a double helix. Meanwhile, the mRNA molecule passes through a pore in the nucleus and proceeds into the cellular cytoplasm where it moves toward the ribosomes....
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