compared with midrange fibroblasts [ population doubling level ( pdl ) = 20 to 30 ] aged fibroblasts ( pdl greater than 40 ] were larger in size in terms of protein and rna per cell , generally proliferated more slowly , exhibited different steady state [ 3h ] proline transfer rna ( trna ) precursor pool specific radioactivities , synthesized collagen at a substantially lower rate , and exhibited a reduction in the percent commitment to collagen synthesis .
C0035668
rna
C0035711
transfer rna