Question

The human insulin gene contains a number of sequences that are removed in the processing of the mRNA transcript. Bacterial cells cannot excise these sequences from mRNA transcripts, yet this gene can be cloned into a bacterial cell and produce insulin. Explain how this is possible.

Short answer

Answer: Bacterial cells are able to produce human insulin by utilizing recombinant DNA technology. Scientists design a synthetic insulin gene without the unnecessary sequences that bacteria cannot process. This synthetic gene is inserted into a vector, typically a plasmid, creating a recombinant DNA molecule. The recombinant DNA is then introduced into bacterial cells, which incorporate the foreign DNA into their genome. As a result, the bacterial cells can correctly process the mRNA transcribed from the synthetic gene and produce human insulin. This insulin is then harvested and purified for medical use.

Step-by-step solution

Understand Recombinant DNA Technology

Recombinant DNA technology is an important biotechnology tool that involves the manipulation and combination of DNA from different sources. This allows for the introduction of new genes, such as the human insulin gene, into a host organism (like bacteria) to produce the desired protein.

Isolate Human Insulin Gene

In order to produce human insulin in bacteria, first, scientists need to isolate the human insulin gene. This gene is extracted from human DNA and then prepared for insertion into a bacterial cell.

Use a Synthetic Gene

The next step would be to design a synthetic human insulin gene that lacks the unnecessary sequences that bacteria cannot process. In this way, scientists can exclude sequences that need to be excised by cellular machinery, thereby making it possible for the bacterial cell to produce functional human insulin.

Construct a Recombinant DNA Molecule

Once the synthetic insulin gene has been designed, it is inserted into a vector, usually a plasmid (a small circular piece of DNA), which will be used to transfer the gene into the bacterial cell. The synthetic insulin gene is then combined with the plasmid to create a recombinant DNA molecule.

Transform Bacterial Cells

The recombinant DNA molecule is then introduced into bacterial cells (usually Escherichia coli) through a process called transformation. During transformation, competent bacterial cells take up the foreign DNA, incorporating it into their own genome.

Protein Expression

Once the recombinant DNA is established in the bacterial cell, the cell's machinery begins to use the synthetic insulin gene to produce human insulin. The bacteria can now synthesize human insulin because they can correctly process the mRNA transcribed from the synthetic gene, which lacks the unnecessary sequences that bacterial cells normally cannot process.

Purify Insulin

Finally, after the bacterial cells have produced human insulin, it is harvested and purified for medical use. This recombinant human insulin can then be administered to individuals with diabetes to help manage their blood glucose levels.

Key concepts

Insulin Gene

The insulin gene is crucial for producing the hormone responsible for regulating blood sugar levels. In humans, the insulin gene contains introns, or non-coding sequences, that need to be removed by cellular machinery during mRNA processing. However, these sequences present a challenge in bacteria because bacterial cells cannot remove introns by themselves.

• In humans, insulin production involves the transcription of the insulin gene into mRNA, followed by the removal of introns in the nucleus.
• Bacterial cells, lacking the necessary splicing machinery, require modified genes to produce insulin.

Recombinant DNA technology addresses this challenge by using synthetic genes, where these introns are already removed before being introduced to bacteria.

Synthetic Gene

A synthetic gene is a man-made version of a natural gene that is modified for specific purposes. In the case of insulin, scientists create a synthetic insulin gene lacking the non-coding sequences that bacteria cannot handle. By doing this, they can ensure that the bacteria can produce a functional protein.

• Synthetic genes are designed to optimize gene expression in the host organism, such as bacteria.
• These genes often exclude unnecessary sequences, making them suitable for straightforward replication and transcription.

The creation of synthetic insulin genes represents one of the most significant advancements in producing insulin on a large scale without relying solely on animal sources.

Protein Expression

Protein expression is the process by which proteins are synthesized from gene sequences within a host organism. In this context, it refers to the bacterial cell's capability to produce human insulin from the recombinant DNA.

• After transformation, bacterial cells use the synthetic insulin gene to transcribe mRNA.
• Ribosomes within the bacterial cells then translate this mRNA into a protein – in this case, insulin.

By utilizing bacterial cells like Escherichia coli, scientists can produce insulin more efficiently and cheaply, providing a stable supply of insulin for therapeutic use.

Transformation

Transformation is the method used to introduce recombinant DNA into bacteria, enabling the production of new proteins. It involves the uptake of external DNA by bacterial cells, which then integrate this DNA and express its genes.

• During transformation, bacterial cells must be made competent to take up foreign DNA, typically through chemical treatments or electrical pulses.
• Once the bacterial cells take up the recombinant plasmid carrying the synthetic insulin gene, they begin to replicate and express the gene.

This process allows bacteria to act as biological factories, efficiently producing human proteins like insulin for medical applications.