A biologist isolated a gene from a human cell, inserted it into a plasmid, and inserted the plasmid into a bacterium. The bacterium made a new protein, but it was nothing like the protein normally produced in a human cell. Why? (Explain your answer.) a. The bacterium had undergone transformation. b. The gene did not have sticky ends. c. The human gene contained introns. d. The gene was not synthesized from scratch.

Verified step by step guidance

1. Understand the process of gene expression: In eukaryotic cells like humans, genes in the DNA contain both exons (coding regions) and introns (non-coding regions). During gene expression, introns are removed through a process called splicing, and only exons are translated into proteins.
2. Recognize the difference in gene expression in prokaryotes: Bacteria, being prokaryotic organisms, do not have the cellular machinery to splice introns from the mRNA transcript. Therefore, if a eukaryotic gene containing introns is inserted into a bacterium, the bacterium will attempt to translate the gene with the introns still present.
3. Identify the impact of introns on protein synthesis in bacteria: The presence of introns in the mRNA transcript can lead to the production of a non-functional or unrelated protein because the mRNA sequence will be read incorrectly by the bacterial ribosomes.
4. Connect the concept to the problem: Since the protein produced by the bacterium was nothing like the protein normally produced in a human cell, it suggests that the issue lies in the processing of the genetic information, specifically the presence of introns which are not correctly handled by the bacterial cell.
5. Conclude the correct answer: The most likely reason for the discrepancy in protein production is that the human gene contained introns (option c), which were not removed by the bacterium, leading to incorrect protein synthesis.

Key Concepts

Gene Expression

Gene expression is the process by which information from a gene is used to synthesize a functional gene product, typically a protein. In eukaryotic cells, this involves transcription of DNA to mRNA, followed by translation of mRNA to protein. Bacteria, however, have different mechanisms for gene expression, which can lead to differences in the proteins produced when eukaryotic genes are expressed in prokaryotic systems.

Introns and Exons

Introns are non-coding sequences within a gene that are transcribed into pre-mRNA but are removed during RNA splicing, leaving only exons, which code for proteins. Bacteria lack the machinery to splice introns out of eukaryotic pre-mRNA, meaning that if a human gene with introns is inserted into a bacterium, the bacterium may not produce the correct protein, as it cannot process the gene properly.

Transformation in Bacteria

Transformation is a process by which bacteria take up foreign DNA from their environment and incorporate it into their own genome. This allows for genetic modification and the expression of new traits. However, the success of transformation and the functionality of the expressed proteins depend on the compatibility of the inserted gene with the bacterial cellular machinery, which can differ significantly from that of eukaryotic cells.