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Processes of Polyadenylation

DNA once transcribed into mRNA it is transported to the cytoplasm. All mRNA’s including specific unspliced mRNA precursors contain the poly A tail with histon mRNA as an exception. But once they are transported to the cytoplasm there exist a poly (A) tail shift that is brought about by the degradation by RNases and rebuilding by cytoplasmic poly (A) polymerase.
Discovery: James Darnell and his coworkers carried out various experiments to study and understand the process of polyadenylation. To begin with, they concentrated on the isolation of the poly (A) tail from the newly synthesized mRNA of the HeLa cell line using two subtypes of the enzyme RNase. The enzymes were;
1. RNase A which function as nucleases that cut after the pyrimidine nucleotides C and G and
2. RNase T1 which cuts after G nucleotides.
Both these enzymes together helped in selection of pure runs of A’s. They then carried out centrifugation to separate the nucleus and cytoplasm to separate them according to their sizes and exposed them to the scintillation counter. The results obtained showed that both peaks of the nucleus and cytoplasm electrophoresed even slower than the 4S-tRNA and 5S-rRNA markers used (size markers). It also confirms the little difference in size that exist between the nuclear and cytoplasmic mRNA poly (A)’s.
Position confirmation: To confirm the 3-prime position of the poly (A) tail they subjected mRNA to an enzyme RNase. On complete digestion it yielded one molecule of adenosine and about 200 molecules of AMP. This result also aided in concluding the size of the poly (A) tail to be about 200 nucleotides long but recent advances and studies have confirmed the size of the poly (A) tail to be about 250nt long.
Activity of poly (A) polymerase: Furthermore it had to confirmed that the poly A tail hadn’t come from DNA transcription as the DNA doesn’t contain long runs of T’s. Therefore being a post transcription modification it stresses on the activity of the poly (A) polymerase that adds AMP residues one at a time to the mRNA synthesized during the transcription process. This can be confirmed with the use of actinomycin D that inhibits DNA-directed transcription but doesn’t inhibit polyadenylation.
Role of the poly (A) tail: 1. Protects mRNA from degradation – Michel Revel and his colleagues studied the same by injecting globin mRNA with and without poly A tail into Xenopus oocyes and measured the rate of its synthesis at various intervals. They found a little difference at first but after 6 hours only the mRNA without the poly (A) tail couldn’t support translation. The simplest explanation they gave regarding the same was that the mRNA with the poly (A) tail had a longer shelf life therefore its protective in nature.
2. Stimulates translation of the attached mRNA- Poly (A)-binding protein (PAB 1) in eukaryotes boost the efficiency of the mRNA translation. This is confirmed by the invitro experiment that contained a capped and poladenylated mRNA

Mukia Maderaspatana Antioxidant Properties

Plants have the ability to synthesize a wide variety of chemical compounds that are used to perform important biological functions and to defend against attack from predators. Mukia maderaspatana (L.)M. Romer, is an annual monoecious climber, belonging to Cucurbitaceae family. This plant specify many medicinal properties such as constipation, cough, vertigo, burning sensation, dyspepsia and dental pain.. In this study, ascorbic acid content from fresh leaves and fruits were carried out. Also, the phytochemical analysis such as Total flavonoid, total phenolics contents of the plant were characterized, and found that leaves of M.maderaspatana is rich in ascorbic acid, an antioxidant than that of fruits and also contains adequate amount of phenolics and flavonoid contents in leaves as compared to fruits.
Keywords: Mukia maderaspatana, Phytochemical activity, Antioxidant activity.
Introduction: Plants (fruits, vegetables, medicinal herbs, etc.) may contain a wide variety of free radical scavenging molecules, such as phenolic compounds (e.g. phenolic acids, flavonoids, lignans, tannins), nitrogen compounds, vitamins, terpenoids (including carotenoids), and some other endogenous metabolites, which are rich in antioxidant activity (; Zheng and Wang, 2001; Cai et al., 2003). Phytochemicals present in plants have been shown to have diverse biological activities like cardioprotective, cancer prevention and inhibiton of bone resorption. One of the most common activities of the phytochemicals is the antioxidant .(B.R.Srilatha and S.Ananda., 2012). The total antioxidant activity of plant foods is the result of individual activities of each of the antioxidant compounds present such as vitamin C, carotenoids, and phenolic compounds, the latter being the major phytochemicals responsible for antioxidant activity of plant materials (Javanmardi, Stushnoff, Locke,