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Q.What is Genetic Code ? What are its characteristics ? OR Write the applications of tissue culture.
Jammu Kashmir JkboseJKBOSE Class 12 Annual Regular Examination 2021Subjective· 3mImportance★★★★★
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Start your 14-day free trial to unlock the full solution →The genetic code is the triplet, degenerate, unambiguous, non-overlapping, commaless, (near) universal code by which mRNA codons specify amino acids, with defined start and stop signals. This question offers a choice — both parts are answered.
Part (i): The Genetic Code and its characteristics
The genetic code is the correspondence between the sequence of nucleotide bases in mRNA (read as codons) and the sequence of amino acids in the polypeptide it specifies; it was deciphered mainly by Har Gobind Khorana, Marshall Nirenberg and Severo Ochoa.
Characteristics:
- Triplet code — a group of three consecutive nucleotide bases (a codon) codes for one amino acid; of the 4³ = 64 possible codons, 61 code for amino acids and 3 are stop codons.
- Degenerate (redundant) — most amino acids are specified by more than one codon (e.g. Leucine has 6 codons), except Methionine (AUG) and Tryptophan (UGG), which have only one codon each.
- Unambiguous and specific — a particular codon always codes for the same, single amino acid; it never codes for two different amino acids.
- Commaless and non-overlapping — the code is read continuously from a fixed starting point, three bases at a time, without skipping any base and without sharing bases between adjacent codons.
- Has start and stop signals — AUG is the initiator/start codon (it also codes for Methionine); UAA, UAG, UGA are stop (nonsense) codons that do not code for any amino acid and signal termination of translation.
- (Nearly) universal — the same codon specifies the same amino acid in virtually all organisms, from bacteria to humans, which is strong evidence for a common evolutionary origin of life (with a few known exceptions, e.g. in mitochondria and some protozoa).
- Colinearity — the linear sequence of codons in mRNA (and the gene) corresponds directly to the linear sequence of amino acids in the polypeptide (established experimentally by Charles Yanofsky).
Part (ii), OR: Applications of tissue culture
- Micropropagation — rapid clonal multiplication of genetically identical, disease-free plants from a small explant.
- Production of virus-free plants via meristem-tip culture. …
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