Question

Read the following statements and according to that, choose the suitable terms for the characteristics of 'genetic option'.
(i) One codon options for only one amino acid.
(ii) Some amino acids are coded by more than one codon.
(iii) The sequence of triplet nitrogenous bases in DNA or mRNA corresponds to one aminoacid sequence in the polypeptide chain.

• A. $Degeneracy & Colinearity & Unambiguous \\ \left(i\right) & \left(i i i\right) & \left(i i i\right)$
• B. $Degeneracy & Colinearity & Unambiguous \\ \left(i i i\right) & \left(i i\right) & \left(i\right)$
• C. $Degeneracy & Colinearity & Unambiguous \\ \left(i i\right) & \left(i i i\right) & \left(i\right)$
• D. $Degeneracy & Colinearity & Unambiguous \\ \left(i\right) & \left(i i\right) & \left(i i i\right)$

Answer 1

Answer: (C)

The genetic code is an inter-relationship between nucleotides sequence of DNA or mRNA and amino acids sequence in a polypeptide.
Salients features of Genetic Code:

1. Triplet code: Each codon is made up of three adjacent nitrogen bases. 61 codons code for amino acids and 3 codons do not code for any amino acids, hence they function as stop codons.
2. Non-ambiguous and specific codons: One codon codes for only one amino acid, hence it is unambiguous and specific. (Exception: GUG is an ambiguous codon, it normally codes for valine but at initiating position, codes for methionine.)
3. Commaless nature: The codon is read in mRNA in a continuous fashion without any punctuations.
4. Degeneracy of code: Some amino acids are coded by more than one codon, hence the code is degenerate. e.g., serine, leucine, arginine by 6 codons, proline, valine, glycine, alanine, and threonine by 4 codons, etc. (Exception: AUG (Met.) and UGG (Trp.) are non-degenerate codons.)
5. Universal code: The code is nearly universal, e.g. UUU would code for phenylalanine in all organisms. Some exceptions to this rule have been found in mitochondria and protozoa.
6. Initiation codon/start signal: AUG has dual functions. It codes for methionine, and, it also acts as an initiator codon.
7. Stop signals: Polypeptide chain termination is signalled by three termination codons- UAA (ochre), UAG (amber) and UGA (opal). They do not specify any amino acids, hence called nonsense codons or stop codons.
8. Non-overlapping codon: Each codon is independent and one codon does not overlap the next codon.