1. What is the cell?
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Answer:
A transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length,that serves as the physical link between the mRNA and the amino acid sequence of proteins. Transfer RNA does this by carrying an amino acid to the protein synthetic machinery of a cell (ribosome) as directed by the complementary recognition of a 3-nucleotide sequence (codon) in a messenger RNA (mRNA) by a 3-nucleotide sequence (anticodon) of the tRNA. As such, tRNAs are a necessary component of translation, the biological synthesis of new proteins in accordance with the genetic code.
Each mRNA molecule is simultaneously translated by many ribosomes, all reading the mRNA from 5′ to 3′ and synthesizing the polypeptide from the N terminus to the C terminus. The complete mRNA/poly-ribosome structure is called a polysome.
tRNAs in eukaryotes
The tRNA molecules are transcribed by RNA polymerase III. Depending on the species, 40 to 60 types of tRNAs exist in the cytoplasm. Specific tRNAs bind to codons on the mRNA template and add the corresponding amino acid to the polypeptide chain. (More accurately, the growing polypeptide chain is added to each new amino acid bound in by a tRNA.)
The transfer RNAs (tRNAs) are structural RNA molecules. In eukaryotes, tRNA mole are transcribed from tRNA genes by RNA polymerase III. Depending on the species, 40 to 60 types of tRNAs exist in the cytoplasm. Serving as adaptors, specific tRNAs bind to sequences on the mRNA template and add the corresponding amino acid to the polypeptide chain. (More accurately, the growing polypeptide chain is added to each new amino acid brought in by a tRNA.) Therefore, tRNAs are the molecules that actually “translate” the language of RNA into the language of proteins.
