Question

If translation begins with the first start codon in the mRNA below, the second codon would be which of the following?

3'-CGGAUGCACUUGACAAUCCGUAGAC-5'
a) 5'-CAC-3'
b) 5'-GGA-3'
c) 5'UGC-3'
d) 5'-CCU-3'

Answer 1

The second codon following the start codon AUG in the mRNA sequence is 5'-CAC-3', which is option (a).

Step-by-step explanation:

The question asks which of the given options would be the second codon in an mRNA sequence if translation begins with the first start codon. When a ribosome translates mRNA, it reads the sequence from the 5' to 3' end. The first codon for translation is always AUG, which codes for methionine. In the provided mRNA sequence, 3'-CGGAUGCACUUGACAAUCCGUAGAC-5', the second codon would follow directly after the AUG start codon. Reading from the 3' to 5' end and translating to the complementary mRNA strand, we would read the sequence in the 5' to 3' direction and identify the first start codon (AUG), which, when flipped to the mRNA's perspective, is written as 5'-AUG-3'. The codon immediately following would be 5'-CAC-3', as it is the complement of the sequence given. Therefore, the second codon after the AUG start codon would be 5'-CAC-3'.