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Molecular Basis of Inheritance — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYMolecular Basis of Inheritance3 Marks
Question
  1. How may codons code for amino acids and how many are unable to do so?
  2. Why are codes said to be.
  1. Degenerate.
  2. Unambiguous.

OR

  1. How many codons code for amino acids and how many do not?
  2. Explain the following giving one example of each.
  1. Unambiguous and specific codon.
  2. Degeneration codon.
  3. Universal codon.
  4. Initiator codon.
✓

Answer

  1. Out of 64 codons 61 code for amino acids and rest 3 codons do not code for any amino acids. These function as stop codons.
  2.  
  1. As codon is a triplet. Out of 64 codons, 6l code for 20 amino acids and 3 codons (UAA, UGA and UAG) do not code for any amino acids. Thus, they function as terminating or stop codons.
  2. Genetic code is uaambiguous and specific. Thus, one codon codes for only one amino acid, e.g. CCU codes only for proline and not for any other amino acid.
  3. Since, rhe number of codons is greater, all of thc amino acids, with exceptions of methionine (AUG) and tryptophan (UGG), are coded by more than one codon, a fearure referred to as the degenerecy of genetic code, e.g. GGU, GGC, GGA and GGG all specifr the same amino acid glycine.
  4. The codon is read in mRNA in a contiguous fuhion, i.e. without puncoration. Thus, the code is commaless.
  5. The genetic code is nearly universal, i.e. particular codon codes for the same amino acid in all organisms except in mitochondrial codons and few Protozoans.
  6. AUG is a codon with dual fi.rncdons. It codes for the amino acid methionine (met) and also acts as an intiator codon.

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