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We studied the development of respiratory tract in bovine embryos by light microscopy and transmission electronic microscopy. This process was observed formation of laryngeal-tracheal tube in embryos that present crown-rump (CR) length of 9.0 mm (20/21 days of pregnancy) at around the fourth gestational week; the organ wall appears to be formed of epithelium comprising several cell layers and supported by mesenchyme. Within the lungs, the areas subjacent to epithelium present condensed mesenchyme, while more distal areas loose mesenchyme, in which blood vessels beginn to form, as the organ is in a pseudo-glandular phase. Ultra-structurally, the mesenchyme cells present irregular shapes, having a stellar or fusiform appearance and are united by desmosomes, where the cytoskeleton attaches to the cellular membrane, forming a connection. The bifurcation of trachea caudal portion in the main bronchia is simultaneous to the appearance of the tracheal bronchi, during the fifth gestational week.

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O paradigma da biologia molecular é definido pelo dogma central, o qual é basicamente subdivido em: replicação do DNA (ácido desoxirribonucléico), que permite a perpetuação da informação gênica; transcrição, que converte a informação do DNA em uma fita de RNA (ácido ribonucléico) complementar; e tradução, que converte a informação contida no RNAm (ácido ribonucléico mensageiro) em proteínas. Tais processos ocorrem por meio do código genético, o qual é composto por conexões entre códons e seus respectivos aminoácidos. [...]