Heterogenous Nuclear RNA - hnRNA

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Ribose Nucleic Acids Comparison Between DNA and RNA Ribosomal RNA (rRNA) Characteristics of Different Ribosome Types Types of rRNA Synthesis of rRNA Messenger RNA (mRNA) Size of mRNA Structure of mRNA Stability of mRNA Synthesis of Messenger RNA - mRNA Polyadenylation Capping in mRNA Methylation in mRNA Heterogenous Nuclear RNA (hnRNA)

Heterogenous Nuclear RNA - hnRNA

Heterogenous Nuclear RNA - hnRNA - Eukaryote cells synthesize heterogenous nuclear RNA (hnRNA) which has been considered to be the precursor of mRNA. Only some hnRNA, however, serves as precursor of mRNA. Most of the hnRNA synthesized in eukaryote cells is rapidly degraded without becoming mRNA.

Heterogenous nuclear RNA is defined as all nuclear RNA, excluding rRNA having a sedimentation coefficient greater than 8S (Weinberg, 1973). Ribosomal RNA from mammalian cells has a high G+C content, while the G+C content of hnRNA is considerably lower. About 20-40% of hnRNA molecules are polyadenylated in mammlian cells.

Their affinity for poly (A) or poly (U) can be used to separate them from rRNA, which has little or no affinity. Heterogenous nuclear RNA undergoes processing to become mRNA. It was previously assumed that hnRNA is cut up into segments, some of which become mRNA. Usually a poly (A) chain is added at the 3' end (polyadenylation).

According to recent suggestions (see Crick, 1978), however, a looping out mechanism takes place during processing, so that splicing as well as elimination of part of hnRNA are involved. This mechanism would permit removal of unrequired segments (loops) and would bring together the required segments of the final mRNA. Different looping behaviour could bring about different types of mRNA from the same type of hnRNA.

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Difference Between Prokaryotes and eukaryotes mRNA Transfer RNA (tRNA) OR Soluble RNA (sRNA) Structure of Transfer RNA - tRNA Unusual Bases in tRNA Classification of tRNA Invariant and Semi invariant Nucleotides Tertiary Structure of tRNA Initiator tRNA Specificity of tRNA Biosynthesis of tRNA Comparison of Different Types of RNA

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