Nucleic acid and protein metabolism in Tribolium confusum Duval : I. The variation of nucleic acid and nucleotide concentration in Tribolium confusum in relation to different stages of its life cycle

Abstract

Summary The variation of deoxyribonucleic acid, ribonucleic acid and free nucleotide concentrations in Tribolium confusum , Duval in relation to different morphological changes has been studied. Considerable variation in the concentration of the two nucleic acids have been found in the embryonic stage as well as during larval phase. The concentrations of the two nucleic acids show, in the beginning, a sharp steady increase, then reach the maximum heights and finally drop rapidly. They remain constant thereafter until the insects are transformed into pupae. When the variation of DNA, RNA and growth with age are all considered together it becomes evident that in insects RNA synthesis precedes protein synthesis (growth) and follows DNA synthesis. The results also indicate that protein synthesis can be considered as an index of growth. It has been noted that the concentrations of free nucleotides measured by optical density determination method and by chemical method (see the experimental section) agree very well when applied to TCA-extracts obtained from insects, upto 14 days old (i.e. as long as the insect can be considered as larva), but when applied to TCA-extracts obtained from pupae or adult insects the results differ widely. The optical density of such TCA-extracts show a steady and sharp increase with age, between 16 to 30 days. This sharp increase in optical density as we have noted suggests that during this period a new compound is synthesised in these insects which interferes with the absorption of the nucleotides at 260 m μ . Addition of uric acid to RNA does not change the absorption of RNA at 260 m μ whereas addition of catechol, a dihydroxyphenolic compound does so. This might be considered to indicate that a compound which can interfere with the absorption of nucleotide at 260 m μ is being continuously synthesised in the insect during the latter stages of its life cycle. In all probability this compound appears to be a polyphenolic compound, the isolation and characterization of which are now being investigated and will be reported separately.