Problem 10 - Campbell Biology Concepts & Connections

Question

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.

Step-by-Step Solution

Answer

c. The human gene contained introns.

Step 1: Understand the problem context

A gene was isolated from a human cell, inserted into a plasmid, and then into a bacterium. The bacterium produced a different protein than the original human cell.

Step 2: Clarify the role of each option

Analyze each multiple-choice option to determine the cause of the discrepancy in protein production. Focus on how bacterial cells differ from human cells in gene expression.

Step 3: Analyze Option a

Option (a) states that the bacterium had undergone transformation. Transformation simply means that the bacterium has taken up foreign DNA, which is true, but it doesn't explain why the protein produced was different.

Step 4: Analyze Option b

Option (b) states that the gene did not have sticky ends. Sticky ends are necessary for the insertion of the gene into the plasmid but do not affect the type of protein produced.

Step 5: Analyze Option c

Option (c) states that the human gene contained introns. Introns are non-coding regions within a gene that eukaryotic cells remove during RNA processing. Bacteria do not have the machinery to remove introns, potentially leading to an incorrect protein being synthesized.

Step 6: Analyze Option d

Option (d) mentions that the gene was not synthesized from scratch. This is not relevant to why the protein produced by the bacterium was different.

Step 7: Conclusion

Since bacteria cannot process introns, the human gene containing introns would not be correctly expressed in a bacterium, resulting in a different protein. Therefore, the correct answer is that the human gene contained introns.

Key Concepts

bacterial_transformation

Bacterial transformation is a process where bacteria take up foreign DNA from their surroundings. This can be natural or induced in the lab.
In this process, a piece of foreign DNA is mixed with the bacteria, which absorbs it through their cell membrane. This can provide bacteria with new traits, such as antibiotic resistance or the ability to produce new proteins.
Key points to understand about bacterial transformation:

• Transformation is crucial in genetic engineering.
• It allows the introduction of new genetic material into bacteria.
• In our exercise, the bacteria were transformed with a human gene.

While transformation explains how the DNA entered the bacteria, it doesn't explain why the proteins produced were incorrect.
That discrepancy is explained by deeper genetic mechanisms.

sticky_ends

Sticky ends are single-stranded overhangs on DNA molecules created by some restriction enzymes when they cut DNA at specific sequences.
These sticky ends allow two pieces of DNA with complementary sticky ends to join together easily.

• Sticky ends are essential in gene cloning and splicing.
• They ensure that DNA fragments can be inserted into plasmids efficiently.
• In the exercise, the gene must have had sticky ends to be inserted into the plasmid.

However, sticky ends do not influence the type of protein produced.
They are merely a tool to ensure the DNA fragments join together correctly.

introns_and_exons

Introns and exons are parts of genes that play roles in coding for proteins.

• Exons are coding regions that specify amino acid sequences in proteins.
• Introns are non-coding regions that are removed during RNA processing in eukaryotes.

Human genes often contain introns that need to be removed for proper protein synthesis.
Bacteria, however, lack the machinery to remove these introns.
This results in the production of abnormal proteins if the introns are not removed. This concept explains why the bacterium in the exercise produced an incorrect protein.
The human gene contained introns, which the bacterium could not process, leading to faulty protein synthesis.

RNA_processing_in_eukaryotes

RNA processing is a critical step in gene expression in eukaryotic cells.
It involves several modifications to pre-mRNA before it becomes mature mRNA.

• Introns are removed, and exons are joined in a process called splicing.
• A 5' cap and a 3' poly-A tail are added to protect mRNA and aid in translation.

These processing steps ensure that the mRNA is correctly translated into functional proteins in eukaryotic cells.
Bacteria do not perform these complex RNA processing steps, which is why they cannot correctly interpret human genes with introns.
Understanding RNA processing highlights the differences in gene expression mechanisms between eukaryotes and prokaryotes, like bacteria.
This knowledge is crucial for genetic engineering and biotechnology applications.