This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Genetic Code”.
1. Which of the following codon calls for fMettRNA –fMet?
a) CTA
b) GUA
c) AUG
d) AUA
View Answer
Explanation: AUG is the start codon for translation, and it incorporates formyl methinonyl tRNA to start translation. The 1st base is always an f-Met although it may be later cleaved off.
2. AUG is the universal start codon.
a) True
b) False
View Answer
Explanation: While there is a common belief of AUG being the universal start codon, mitochondrial ribosomes doesn’t recognize it as so. Also GUG can act as a start codon in some cases undermining AUG.
3. What is meant by degenerate codon?
a) Two codons can be read in different frame o give different amino acids
b) Codons are not having a gap
c) Specific codon codes for specific amino acid
d) Two codons can code for same amino acid
View Answer
Explanation: Degeneracy means that there can be two or more codons that can code for same amino acid with there being triplet codon and 4 bases there are 64 possible combinations and only 20 amino acids. This was then observed that different codon could be degenerate i.e. code for same amino acid.
4. Consider that our codon in place of being triplet was quadruplet. How many possible combinations could be there then?
a) 64
b) 128
c) 256
d) 360
View Answer
Explanation: There are 4 DNA bases and triplet coodon so number of possible combinations id 43=64. Now if the codon was quadruplet the combinations would be 44=256.
5. Which of the following is not a stop codon?
a) UAA
b) GUG
c) UAG
d) UGA
View Answer
Explanation: GUG is not a stop codon, rather it is a start codon which can be used in place of AUG. On the other hand UAA, UAG and UGA are stop codons.
6. In an experiment if you add poly A oigon-dNTP in a nucleotide free cell lysate. Which of the labeled amino acid do you expect to be incorporated in the peptide so formed?
a) Lys
b) Phe
c) Pro
d) Leu
View Answer
Explanation: While poly A oligo-rNTP would incorporate lysine, due to repeated AAA codon, oligo-dNTP actually makes poly U oligo-rNTP, having codon UUU that codes for Phenyl alanine.
7. Wooble base hypothesis is applicable to the____________
a) Mitochondrial codon
b) 1st base in codon
c) 2nd base in codon
d) 3rd base in codon
View Answer
Explanation: Wooble hypothesis states that the 1st anticodon of the tRNA is not very specific. So it can pair with upto 3 different bases in the codons 3rd position.
8. If you consider wooble hypothesis I in 1st position of anticodon can not pair with?
a) A is 3rd position of codon
b) U is 3rd position of codon
c) G is 3rd position of codon
d) C is 3rd position of codon
View Answer
Explanation: I is the ionosine base that can pair with A, U and C in the 3rd position of the codon. But it can’t pair with G or itself.
9. State whether it is true that degeneracy can act as a mode of control in RNA?
a) True
b) False
View Answer
Explanation: The tRNA against all the degenerate codons for an amino acid are not present in the same concentration in the cell. Thus, it can sometimes stall the polymerase as in trp operon. Even in eukaryotes this stalling of polymerase could lead to domain formation.
10. Which of these mutations will have the least harmful effect?
a) Addition of 2 bases
b) Deletion of 3 bases
c) Transition of one base
d) Deletion of a chunk
View Answer
Explanation: In all possibilities transition of a base would have least harmful effect as there are degenerate codons for same amino acid. The new codon could thus be a silent mutation. Also if it is the 3rd base due to wooble hypothesis it will have negligible effect.
11. If you charge a lys-tRNA with an alanine, what amino acid will you expect to be incorporated against AAA?
a) Lysine
b) Alanine
c) Phenylalanine
d) f-alanine
View Answer
Explanation: The anticodon loop plays no part in recognizing the amino acid. It can simply recognize the codon. So, it will call in the Ala charged lysine-tRNA to alysine AAA codon and add the alanine to the peptide.
Sanfoundry Global Education & Learning Series – Cytogenetics.
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