"(1)Describe the structure and function of a tRNA molecule . Why it is reffered as an adapter molecule?(2)Explain the process of hnRNA in eukaryotic cell?"
class 12th CBSE Biology sample paper
Answers
The tRNA, was known before the genetic code was postulated. However, its role as an adapter molecule was assigned much later.
The tRNA stands for TRANSFER RNA.
tRNA has an anticodon loop that has bases complementary to the code, and it also has an amino acid accepter end to which it binds to amino acids. tRNAs are specific for each amino acid.
For initiation, there is another specific tRNA that is referred to as initiator tRNA. There are no tRNAs for stop codons.
the secondary structure of tRNA has been depicted that looks like a clover-leaf. In actual structure, the tRNA is a compact molecule which looks like inverted L.
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(2). The RNA polymerase II transcribes precursor of mRNA, the heterogeneous nuclear RNA (hnRNA).
hnRNA undergo two additional processing called as capping and tailing. In capping an unusual nucleotide (methyl guanosine triphosphate) is added to the 5'-end of hnRNA. In tailing, adenylate residues (200-300) are added at 3'-end in a template independent manner. It is the fully processed hnRNA, now called mRNA, that is transported out of the nucleus for translation