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Genetic Code - Practice Questions & MCQ
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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25 Questions around this concept.
Solve by difficulty
Whose experiments cracked the DNA and discovered unequivocally that a genetic code is a 'triplet'
Which of the following statements are correct about genetic code?
I. It contains 65 codons
II. AUG codes for methionine amino acid
III. The same amino acid is coded for by the multiple codons.
IV. Genetic codon codes for mRNA
The one aspect which is not a salient feature of genetic code, is its being:
What is not true for genetic code?
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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