Sample 1Easy
Which codon codes for methionine and also acts as the initiator codon?
- A
UAA
- B
UAG
- C
AUG
- D
UGA
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The answer is C.AUG has dual functions: it codes for methionine and it also acts as the initiator codon. UAA, UAG and UGA are stop codons that code for no amino acid.
- A.
UAA is a stop (terminator) codon.
- B.
UAG is a stop (terminator) codon.
- D.
UGA is a stop (terminator) codon.
NCERT: Class 12 Biology, Chapter 5 (Molecular Basis of Inheritance), Genetic Code
Sample 2Medium
A schematic transcription unit shows double-stranded DNA: the upper strand, running 5'→3', is the coding strand and the lower, running 3'→5', is the template strand. A promoter is at the left (upstream), the structural gene in the middle and a terminator at the right. In the structural gene, the coding strand reads 5'-ATGCATGC-3'. What is the sequence of the mRNA transcribed?
- A
3'-UACGUACG-5'
- B
5'-ATGCATGC-3'
- C
5'-CGUACGUA-3'
- D
5'-AUGCAUGC-3'
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The answer is D.The mRNA is complementary to the template strand, so it has the same sequence and polarity as the coding strand, with uracil in place of thymine. Here that is 5'-AUGCAUGC-3'.
- A.
This is complementary to the coding strand; the mRNA is complementary to the template strand.
- B.
RNA has uracil in place of thymine.
- C.
This is the right bases written with the wrong polarity.
NCERT: Class 12 Biology, Chapter 5, 5.5