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| Ribose Nucleic Acid (RNA) |
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| RNA occurs mostly in the cytoplasm in the eukaryotic cells. A small amount occurs in the nucleus of the cell, as a constituent of nucleolus. |
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| RNA is a single polynucleotide chain composed of nucleotides of adenine, guanine, cytosine and uracil. Thymine nucleotides are absent. |
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| There are three types of RNA |
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| Messenger RNA (mRNA) |
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| It represents about 5 to 10% of the total RNA. It is synthesised from DNA as and when necessary. It carries the genetic information in the form of a specific sequence of nitrogen bases arranged in triplet codons, which are copies from the code in DNA. |
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| Transfer RNA (tRNA) |
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| It represents about 10 to 15% of the total RNA in the cell. It has the shortest molecule having only about 80 to 100 nucleotides. The polynucleotide chain is folded on itself to have the shape of a cloverleaf. The molecule has three lateral loops, a DHU loop, a t loop and an anticodon loop. The anticodon loop bears a triplet combination of nitrogen bases, called anticodon. It is complementary to a codon of mRNA. |
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| The tRNA molecule is meant for recognising and carrying particular types of amino acids to the sites of protein synthesis. |
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| Ribosomal RNA (rRNA) |
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| It represents nearly 80% of the total RNA in the cell. It always occurs bound to basic proteins in ribosomes. It takes part in assembling the amino acids brought by tRNA, into a polypeptide chain, based on the sequence of codons in mRNA. |
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| RNA serves the following functions: |
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 mRNA has a significant role in genetic code. |
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 tRNA is responsible for transferring amino acids to the site of protein synthesis (ribosomes). |
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 rRNA assembles the amino acids into a polypeptide chain. It also serves as a primer for replication of DNA. |
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 RNA serves as the genetic material in some plant viruses. |
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