 chang nucleic acid phospholipid level liver cours fetal postnat develop evolut dna rna pl liver rat foeti remov fifteenth twenti-first dai gestat young rat newli-born wean observ fact 1 dna concentr 1100 ug 15th dai decreas 19th dai reach 280 ug 5 dai wean 2 rna concentr 1400 ug 15th dai decreas 820 period 3 pl concentr low 15th dai foetal life 700 ug increas abruptli birth 4 ratio rna cyto dna pl cyto dna increas regularli 18th dai foetal life 5 nuclear rna pl content high develop 6 enabl character three stage develop rat liver - 15th dai 18th dai foetal life stage growth hyperplasia hypertrophi - 19th dai foetal life 3rd dai post-natal life stage cellular reorganis - 3rd dai post-natal life stage growth hyperplasia hypertrophi 