Learning Objectives

• Define the steps involved in producing a recombinant DNA molecule.
• Identify the roles of restriction endonucleases and DNA ligase.
• Recognize clinical applications, such as the production of human insulin.

1. The Process of Recombinant DNA Production

Molecular cloning involves inserting a DNA fragment of interest (e.g., a human gene) into a bacterial plasmid or a eukaryotic vector to produce large quantities of a specific protein.

1. Isolation: The target DNA sequence (e.g., human cDNA) is isolated.
2. Digestion: Both the target DNA and the plasmid vector are cut using the same restriction endonucleases. This creates “sticky ends” that are complementary to each other.
3. Ligation: The DNA fragment is inserted into the plasmid and permanently joined by DNA ligase.
4. Transformation: The recombinant plasmid is introduced into a host cell (usually E. coli) through a process called transformation.

Activity

2. Selection and Expression

To ensure only the cells containing the recombinant plasmid grow, a selection marker (typically an antibiotic resistance gene) is used.

• Antibiotic Selection: Only bacteria that took up the plasmid (carrying the resistance gene) will survive on media containing that antibiotic.
• Protein Production: The host cell’s machinery transcribes and translates the inserted gene, producing the human protein.

Activity

3. Clinical Applications

Molecular cloning is the foundation of biotechnology and modern pharmacology, allowing for the mass production of essential human proteins:

• Human Insulin: Replacing older animal-derived insulin with bioidentical human insulin.
• Human Growth Hormone (GH): Used for the treatment of growth hormone deficiencies.
• Clotting Factors: Production of Factor VIII for patients with Hemophilia A.

Activity