A certain gene in a bacterium codes for a polypeptide that is 120 amino acids long. How many nucleotides are needed in the mRNA to code for this polypeptide?
A. 30
B. 40
C. 360
D. 480



Answer :

The answer is C. 360.

3 nucleotides correspond to 1 amino acid (this is an important fact to remember). Therefore, to create a polypeptide 120 amino acids long, the mRNA "message" would need to be 3 times that length, or 360 nucleotides.

If one gene codes a polypeptide containing 120 amino acids long, then 360 nucleotides will be needed in the mRNA to code for this polypeptide (Option C).

  • During gene transcription, a specific sequence of DNA called 'gene' is used as a template to create a messenger RNA (mRNA).

  • Subsequently, this mRNA is then used to create a protein via the process of translation.

  • The triplets of nucleotides or 'codons' of this mRNA will specify the linear order of amino acids that are added to the growing polypeptide during translation.

  • In consequence, each amino acid is determined by three sequential nucleotides (i.e., a codon), thereby 120 amino acids are determined by 360 nucleotides (120 x 3 = 360 nucleotides).

In conclusion, if one gene codes a polypeptide containing 120 amino acids long, then 360 nucleotides will be needed in the mRNA to code for this polypeptide (Option C).

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