By the end of this lesson
- Define a vector in genetic modification.
- Describe how plasmids are used as vectors.
- Describe how viruses are used as vectors.
BIG QUESTION
How do you get a new gene inside a living cell?
Scientists use carriers that cells already take in: small bacterial DNA rings or viruses that inject their DNA.
What a vector does
A vectorSomething used to carry DNA into a cell in genetic engineering, such as a plasmid or a virus. is something used to carry a piece of DNA into another cell. The wanted gene is inserted into the vector, making recombinant DNADNA made by joining DNA from two different sources, such as a human gene in a bacterial plasmid., and the vector then transfers it into a host cellA cell that a virus infects, or that receives a recombinant plasmid in genetic engineering..
The two vectors named in the specification are plasmidA small ring of DNA in a bacterial cell, separate from the main chromosome, used as a vector in genetic engineering. and virusA non-living, acellular particle of genetic material in a protein coat that can only reproduce inside a living host cell..
Plasmids
A plasmid is a small circular loop of DNA found in bacteria, separate from the main chromosome. It is cut with a restriction enzyme, the gene is inserted and ligase seals it.
Bacteria are then mixed with the recombinant plasmids; some take them up. These bacteria are genetically modifiedDescribes an organism whose DNA has been changed by genetic engineering, usually by inserting a gene from another organism. and copy the plasmid each time they divide.
Viruses
A virus naturally injects its genetic material into a host cell. Scientists can insert a gene into a virus’s DNA so that, when the virus infects a cell, it delivers the gene.
Viruses that infect bacteria (bacteriophageA virus that infects bacteria; it can be used as a vector to carry genes into bacterial cells.) can be used for bacterial hosts; other modified viruses can deliver genes to plant or animal cells. Harmful viral genes are usually removed first.
Plasmid and virus vectors
Both carry recombinant DNA but enter cells differently.
| Feature | Plasmid | Virus |
|---|---|---|
| Origin | Small DNA loop from bacteria. | Viral genetic material. |
| How DNA enters host | Taken up by bacteria from surroundings. | Injected when the virus infects the cell. |
| Typical host | Bacteria (e.g. for insulin). | Bacteria, plant or animal cells. |
Language that earns precision
- vector
- A carrier used to transfer DNA into a cell.
- plasmid
- A small circular loop of DNA in bacteria.
- host cell
- The cell that receives the recombinant DNA.
- genetically modified
- Having had its DNA altered by genetic engineering.
Common misconceptions
Claim: All bacteria take up the plasmid.
Correction: Only some bacteria take it up, so successful ones must be identified.
Claim: A vector is the gene itself.
Correction: The vector is the carrier; the gene is inserted into it.
Claim: Viral vectors make the host ill.
Correction: Harmful viral genes are usually removed before use.
Match the answer to the command word
A vector carries DNA into another cell; name plasmids and viruses as examples.
Order the steps: cut plasmid, insert gene, ligase, take up by host, host multiplies.
Recall, apply, then justify
What is meant by a vector in genetic modification?
Hint
Its job.
Suggested marking points
- Something that carries / transfers DNA (a gene) into another cell.
Describe how a virus can act as a vector.
Hint
Insert, infect, deliver.
Suggested marking points
- The gene is inserted into the virus DNA.
- The virus infects / attaches to a host cell.
- It injects / delivers the recombinant DNA into the host cell.
Compare the use of plasmids and viruses as vectors for genetic modification.
Planning hint
Similarities and differences.
What a strong design includes
- Both carry the wanted gene as recombinant DNA.
- Both are cut with restriction enzymes and joined with ligase.
- Plasmids are circular DNA from bacteria.
- Plasmids are taken up by bacteria from their surroundings.
- Viruses inject DNA when they infect a host cell.
- Viruses can be used to deliver genes to plant or animal cells.