Ribonucleic acid triplet code

The ribosome is the enzyme that catalyzes peptide bond formation. The bacterial ribosome is a large 2500 kDa ribonucleic acid/protein complex comprised of a large subunit (LSU or SOS subunit) and a small subunit (SSU or 30S subunit) (Fig. 4.1). The small ribosomal subunit binds to messenger RNA (mRNA) and reads the genetic code by aligning its base triplet codons with anticodons of transfer RNA molecules (tRNA). The large ribosomal subunit binds to opposite ends of tRNA molecules and catalyzes peptide bond formation. 

The mRNA leaves the nucleus and attaches itself to ribosomal ribonucleic acid (rRNA) in the cytoplasm of the cell. Without going into precise detail, rRNA reads the base-sequence code of mRNA and a third type of RNA, transfer ribonucleic acid (tRNA) brings the correct amino acid to the forming protein. This process is known as translation. Each amino acid is coded for by a sequence of three bases, known as a triplet code. For example, ACA codes for the amino acid cysteine. As amino acids are added in sequence a protein is built up. 

In other investigations an attempt was made to detect changes in the nucleotide composition of RNA in connection with the phases of embryogenesis and tissue differentiation (Makhin ko and Blok, 1961 Mazurov and Orekhovich, 1963 Nemeth and Dickerman, 1960 Burch and Von Dippe, 1964 Comb and Brown, 1964 Deuchar and Bristow, 1965). However, no precise principles were established, because determinations of the total nucleotide composition of RNA may fail to detect differences in the actual information carried on account of degeneracy of the code and because of the triplet (trinucleotide) alphabet used to record the information. Obviously, therefore, only a much finer and more functional fractionation of the ribonucleic acids can provide an accurate indication of the regulatory functions of the cell nucleus in morphogenesis. 

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