Human Biochemistry, Volume 2 - Murray R. 1993

Structure, Function, and Replication of Information Macromolecules
Protein Synthesis and the Genetic Code
Information Flow

Genetic information encoded in the DNA nucleotide sequence is transcribed in The Nucleus into specific nucleotide sequences of RNA molecules. The nucleotide sequence of the RNA transcript is complementary to the coding strand of the Gene in accordance with the base-pairing rules.

In prokaryotes, There is a direct correspondence between the gene, Messenger RNA (mRNA), and the protein product. The situation is more complex in higher Eukaryotic Cells, where the size of primary RNA transcripts—heterogeneous nuclear RNA (hnRNA)—significantly exceeds that of mature mRNA. The hnRNA sequences contain coding regions (exons), which subsequently form mature mRNAs, and extended intervening non-coding sequences (introns) located between the exons. As a result of hnRNA Processing taking place in the Cell Nucleus, the introns, which often constitute the major part of the hnRNA, are removed. Through a process known as splicing, the exons are joined together, and the resulting mature mRNA is transported to the Cytoplasm, where it is translated into protein.

Cells must possess specialized Mechanisms for the precise, accurate, and efficient Translation of an mRNA sequence into the corresponding Amino Acid Sequence of the encoded protein. Elucidating the Molecular Basis of this process, termed translation, required cracking METABOLISM/28.html">The Genetic Code. It soon became apparent that mRNA molecules themselves possess no inherent affinity for Amino Acids; therefore, translating the nucleotide sequence of mRNA into protein requires an intermediate adaptor molecule. This molecule must recognize, on the one hand, a specific mRNA sequence and, on the other hand, a specific amino acid. Through such a molecule, The Cell can direct a specific amino acid to the appropriate position in the synthesized protein molecule, as dictated by the mRNA nucleotide sequence. The Functional groups of amino acids do not directly contact the mRNA template on their own.