Problem 6 - Campbell Biology

Question

Expression of a cloned eukaryotic gene in a bacterial cell involves many challenges. The use of mRNA and reverse transcriptase is part of a strategy to solve the problem of (A) post-transcriptional processing. (B) post-translational processing. (C) nucleic acid hybridization. (D) restriction fragment ligation.

Step-by-Step Solution

Answer

A post-transcriptional processing

Step 1: Understand the Problem

Expression of a cloned eukaryotic gene in a bacterial cell faces challenges because eukaryotic genes often contain introns that bacteria can't process.

Step 2: Role of mRNA

mRNA is a mature transcript that has undergone post-transcriptional processing, including splicing to remove introns.

Step 3: Role of Reverse Transcriptase

Reverse transcriptase synthesizes a complementary DNA (cDNA) from the processed mRNA, effectively creating an intron-free version of the gene that bacteria can express.

Step 4: Identify the Correct Answer

Using mRNA and reverse transcriptase bypasses the need for intron removal, addressing the issue of post-transcriptional processing.

Key Concepts

Eukaryotic Gene Expression

Gene expression in eukaryotes involves multiple steps to convert DNA into a functional product like a protein. The process includes transcription (copying DNA to RNA) and translation (RNA to protein). Unlike bacteria, eukaryotic genes contain introns, non-coding sequences that need removal before translation. This removal happens during post-transcriptional processing. Eukaryotic genes also have regulatory elements like enhancers and promoters.
Due to the complexity of eukaryotic gene expression, transferring these genes to bacteria for expression presents challenges. Bacteria lack the machinery to process introns; hence, direct expression of eukaryotic genes in bacteria is troublesome. Key steps to consider include:

• Transcription: DNA to RNA conversion with intron exons
• Splicing: Removal of introns
• Translation: RNA to protein conversion

Reverse Transcriptase

Reverse transcriptase is an enzyme that converts RNA into complementary DNA (cDNA). This enzyme is essential for overcoming intron processing challenges when expressing eukaryotic genes in bacteria. Here's how it works:
Instead of directly cloning DNA with introns into bacteria, researchers first transcribe the eukaryotic gene into mRNA, a mature form without introns. Then, using reverse transcriptase, this mRNA is converted into cDNA. This cDNA can be introduced into bacteria.
The use of reverse transcriptase has several steps:

• mRNA transcription: Produce mature mRNA
• cDNA synthesis: Convert mRNA to cDNA using reverse transcriptase
• Cloning: Insert cDNA into bacteria for expression

Reverse transcriptase ensures the bacterial expression of eukaryotic genes, bypassing post-transcriptional processing issues like intron removal.

Post-Transcriptional Processing

Post-transcriptional processing is critical for converting a primary RNA transcript into mature RNA, especially in eukaryotes. This processing includes several modifications:

• Splicing: Removal of introns and joining of exons
• 5' Capping: Adding a modified guanine nucleotide to the RNA's 5' end
• Polyadenylation: Adding a tail of adenine bases to the RNA's 3' end

The splicing process is crucial because eukaryotic genes consist of both introns and exons. Bacteria cannot deal with introns, making direct gene expression impossible without further steps.
To address these issues, mature mRNA (already processed) is converted to cDNA using reverse transcriptase before transferring to bacteria. This avoids intron-related problems, allowing efficient gene expression in a bacterial environment. Understanding post-transcriptional processing is essential for genetic engineering and biotechnology applications.