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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# Recombinant DNA and cloning

Recombinant DNA technology cuts and joins DNA from different sources so that a host cell makes a protein or copies a gene.

Updated 2026-11-01

## Key facts

- Restriction enzymes cut specific palindromic sequences (e.g. EcoRI, GAATTC), leaving sticky or blunt ends.
- DNA ligase joins the fragment to the vector (plasmid or virus).
- The plasmid carries an origin of replication, an antibiotic resistance gene (selection) and a multiple cloning site.
- cDNA is made from mRNA with reverse transcriptase: it has no introns, so bacteria can express it.
- Classic products: human insulin, growth hormone, erythropoietin, factor VIII, hepatitis B vaccine.

## In detail

- 1. Get the gene: by PCR, from cDNA or by chemical synthesis.
- 2. Cut the gene and the vector with the same restriction enzyme so their ends match.
- 3. Join with DNA ligase and put the vector into the host cell (transformation in bacteria, transfection in animal cells).
- 4. Select the cells that took it up with the antibiotic; blue/white screening (disrupted lacZ) spots those carrying an insert.
- 5. Express the protein: bacteria (cheap, no glycosylation), yeast or mammalian cells (human-type glycosylation, as for erythropoietin).
- Restriction fragment length polymorphisms (RFLP): a mutation that creates or destroys a cut site changes fragment sizes; the basis of classic molecular diagnosis of sickle cell disease.

## Clinical notes

- Recombinant human insulin replaced animal insulin and reduced immune reactions.
- Transgenic and knockout animals let researchers study human diseases in the lab.

## Related conditions

- [Type 1 diabetes mellitus](https://durgical.com/en/conditions/type-1-diabetes-mellitus/)

## Related

- [Polymerase chain reaction (PCR)](https://durgical.com/en/biochemistry/topics/polymerase-chain-reaction/)
- [DNA sequencing](https://durgical.com/en/biochemistry/topics/dna-sequencing/)
- [Gene therapy](https://durgical.com/en/biochemistry/topics/gene-therapy/)
- [CRISPR-Cas9 and genome editing](https://durgical.com/en/biochemistry/topics/crispr-cas9-and-genome-editing/)
- [The lac operon and gene regulation in bacteria](https://durgical.com/en/biochemistry/topics/the-lac-operon-and-gene-regulation-in-bacteria/)

## Test yourself

Think of the answer, then tap the question to see it.

## Why is cDNA rather than genomic DNA cloned to express a human protein in bacteria?

Bacteria do not splice; cDNA, copied from mature mRNA, has no introns.

## What kind of sequence do restriction enzymes recognise?

Short palindromic sequences (reading the same 5'→3' on both strands), such as GAATTC for EcoRI.

## Why does a plasmid carry an antibiotic resistance gene?

For selection: only bacteria that took up the plasmid survive on the antibiotic medium.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Recombinant DNA Technology](https://www.genome.gov/genetics-glossary/Recombinant-DNA-Technology) (National Human Genome Research Institute (NHGRI), 2026); [Restriction Enzyme](https://www.genome.gov/genetics-glossary/Restriction-Enzyme) (National Human Genome Research Institute (NHGRI), 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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