Genetic engineering moves a useful gene into a host cell so that the host makes a new protein. Explaining it means giving each step in order, with the job of each tool.
This lesson opens the genetic technology lessons in SPM Biology. It links to inheritance, because the gene is a section of DNA that codes for a protein.
What are the steps?
Here is an original six-step chain for making a protein in a bacterium.
| Step | What happens | Tool or structure |
|---|---|---|
| 1 | Identify and isolate the useful gene | Source cell DNA |
| 2 | Cut the gene out and cut the carrier open | Restriction enzyme |
| 3 | Join the gene into the carrier | DNA ligase |
| 4 | Place the recombinant plasmid in a host cell | Bacterium |
| 5 | Grow the host cells in large numbers | Culture medium |
| 6 | Collect the protein the host produces | Extraction |
The plasmid acts as a carrier. The host cell reads the gene and makes the protein.
Worked example: a three-mark answer
Question: explain how a human gene is inserted into a bacterial plasmid.
- A restriction enzyme cuts the human gene from the DNA and cuts the plasmid open, leaving matching ends.
- The gene is placed in the opened plasmid, and DNA ligase joins the two, forming a recombinant plasmid.
- The recombinant plasmid is placed into a bacterium, which then makes the protein coded by the gene.
Each sentence names the tool and what it does to the DNA.
The mistake that costs marks
The common slip is to swap the enzyme jobs. A student writes that ligase cuts the gene out, or that restriction enzymes join the gene to the plasmid.
| Claim | Why it fails |
|---|---|
| “Ligase cuts the gene out” | Ligase joins DNA pieces |
| “Restriction enzyme joins the gene to the plasmid” | It cuts DNA at a specific sequence |
| Correct: “Restriction enzyme cuts, then ligase joins” | Cut first, join second |
A memory aid: ligase and ligament both join things together.
Check yourself
State the purpose of growing the host cells in large numbers after the recombinant plasmid is inserted.
Answer
Each host cell carries the new gene and makes the protein. Growing many cells produces the protein in a larger amount, which is what makes the process useful for making a product.
What to study next
Practise reading a diagram of this chain in interpreting a genetic-technology diagram. Then try the genetic technology practice set.
If you want a teacher to go through the chain with you, see online one-to-one Biology tuition.