Q.A bacterial cell was transformed with a recombinant DNA molecule that was generated using a human gene. However, the transformed cells did not produce the desired protein. Reasons could be:

The transformed bacterial cell can fail to produce the desired human protein for two genuine reasons: (a) the human gene may contain introns that bacteria cannot splice out, and (c) even a correctly-made human protein can be recognised as foreign and degraded by the bacterium's own proteolytic machinery.

Option (b) — "amino acid codons for humans and bacteria are different" — is a FALSE premise if read literally: the genetic code is essentially universal across all life (with only rare, minor exceptions such as some mitochondrial codes), so the same codon specifies the same amino acid in a human cell and a bacterial cell. Since one of the three named reasons is not actuall …

Let's examine each option on its own merits.

Option (a): Human gene may have intron which bacteria cannot process — This is a genuine, well-established reason. Human genes are split into coding sequences (exons) interrupted by non-coding introns; a spliceosome removes these introns after transcription in human cells. Bacteria are prokaryotes with no introns of their own and no spliceosome. If the human gene's genomic (intron-containing) form is inserted directly, the bacterium cannot remove the introns, and the resulting RNA cannot be correctly translated. This is exactly why cDNA (made from already-spliced mature mRNA) is used, not genomic DNA, when expressing a eukaryotic gene in bacteria.

Option (b): Amino acid codons for humans and bacteria are different — This statement, read as written, is FALSE. The genetic code is (with only rare, minor exceptions, e.g. some mitochondrial genomes) universal: the same codon specifies the same amino acid in every organism, human or bacterial. Since this option asserts something that is not actually true, it cannot be counted as a genuine reason for expression failure. …

Alternative Approach: A Requirements Checklist for Expressing a Foreign Gene

Treat "express a human gene in bacteria" as a checklist of requirements the bacterial

cell must satisfy, and test each option against real biology, not just plausibility.

Step 1: Can the bacterium copy the gene into RNA (transcription)?

Yes, given a bacterial-recognised promoter — routine, not the usual point of failure.

Step 2: Can the bacterium correctly PROCESS that RNA into a usable form?

No, if the genomic (intron-containing) version of the gene is used — bacteria have

no spliceosome and cannot remove introns. This is option (a), and it is a genuine,

real reason for failure.

Step 3: Can the bacterium correctly TRANSLATE the mRNA using its own codon table?

Yes — the genetic code is universal (with only rare exceptions) across all life, so a

codon specifying a given amino acid in a human cell specifies the SAME amino acid in a

bacterial cell. Option (b), read as written ("amino acid codons... are different"), is

simply false — this is not a genuine reason for expression failure, however plausible

it sounds.

Step 4: Once made, will the bacterium keep the protein intact? …