Question

When using bacteria to clone a human gene and express its product-as in the case of insulin-the gene cannot contain introns because bacteria do not have the enzymes to process mRNA. Therefore

• A. if the sequence is known, very small human genes can be built with a DNA synthesizer in a laboratory and they will lack introns
• B. reverse transcriptase can be used to make DNA backwards from human mature mRNA and this would lack introns
• C. it is impossible to use bacteria to express human gene products because all human genes have introns
• D. both (a) and (b) are true

Answer 1

The correct option is D both (a) and (b) are true

In order for a human gene to be expressed in bacteria, it must have one important modification. Specifically, it must lack introns. Introns are intervening sequences found in many human genes, and they are removed from eukaryotic RNA transcripts by splicing to make a mature mRNA. Bacteria lack enzymes for splicing. This problem is tackled by using the following approaches:-

1. Reverse transcriptase is used to make DNA backwards from human mature mRNA. This DNA will lack introns and DNA will contain only those genes that are going to be expressed.
   
2. Artificial gene synthesis by building polynucleotide chain based on the sequence of nucleotides in DNA fragment of the gene of interest.

So, the correct option is 'both (a) and (b) are true'.