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Genetic Code MCQ - Practice Questions with Answers
Edited By admin | Updated on Sep 18, 2023 18:34 AM | #NEET
Quick Facts
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Salient Features of Genetic Code is considered one of the most asked concept.
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24 Questions around this concept.
Solve by difficulty
Whose experiments cracked the DNA and discovered unequivocally that a genetic code is a 'triplet'
The one aspect which is not a salient feature of genetic code, is its being:
What is not true for genetic code?
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If one strand of DNA has the nitrogenous base sequence at ATCTG, what would be the complementary RNA strand sequence
Concepts Covered - 2
Genetic Code
- During replication and transcription, nucleic acid was copied to form another nucleic acid.
- Hence, these processes are easy to conceptualize on the basis of complementarity.
- The process of translation requires the transfer of genetic information from a polymer of nucleotides to a polymer of amino acids.
- Neither does any complementarity exist between nucleotides and amino acids, nor could any be drawn theoretically.
- The nucleic acids being polynucleotide, function to store genetic information and to replicate.
- The genetic information flows from polynucleotide to polypeptide.
- The genetic code is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells.
- There are four alphabets (A, G, T, C) of DNA.
- We know that there are 20 different amino acids that constitute a protein as the nitrogen bases constitute nucleotides.
- It was George Gamow, a physicist, who argued that since there are only 4 bases and if they have to code for 20 amino acids, the code should constitute a combination of bases
- H suggested that in order to code for all the 20 amino acids, the code should be made up of three nucleotides.
- This was a very bold proposition because a permutation combination of
(4 × 4 × 4) would generate 64 codons; generating many more codons than required.
- The chemical method developed by Har Gobind Khorana provided proof that the codon was a triplet by synthesizing RNA molecules with defined combinations of bases (homopolymers and copolymers).
- Marshall Nirenberg’s cell-free system for protein synthesis finally helped the code to be deciphered.
- Severo Ochoa enzyme (polynucleotide phosphorylase) was also helpful in polymerizing RNA with defined sequences in a template-independent manner (enzymatic synthesis of RNA).
Salient Features of Genetic Code
- Sixty one codons correspond to amino acids.
- Four codons are the signals.
- There are three stop codons (UAA, UAG, and UGA) and one start codon (AUG). Rarely, GUG also acts as a starting codon.
- AUG also codes for the amino acid methionine.
- The Code is degenerate:
- It means that more than one codon code for individual amino acid.
- For example, codons starting with CC specify proline (CCU, CCC, CCA, and CCG) and all codons starting with AC specify threonine (ACU, ACC, ACA, and ACG).
- The Code is non-overlapping:
- The genetic code is non-overlapping which means that the same letter does not take part in the formation of more than one codon.
- The Code is Unambiguous:
- It means that a particular codon will always code for the same amino acid.
- The codon is read in mRNA in a contiguous fashion. There is no punctuation.
- The code is nearly universal: for example, from bacteria to human UUU would code for Phenylalanine (phe). Some exceptions to this rule have been found in mitochondrial codons, and in some protozoans.
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