Trace bacterial production of a human protein
A human gene can be cut and joined into a bacterial plasmid, transferred to bacteria, multiplied and expressed to make the human protein.
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Know that genes are sections of DNA and that organisms use enzymes in cellular processes.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What does DNA ligase do in the taught genetic-modification process?
What you will learn
- Sequence the syllabus steps for bacterial production of a human protein
- Explain the roles of restriction enzymes, sticky ends, DNA ligase and recombinant plasmids
Build a recombinant plasmid
A restriction enzyme cuts DNA at a particular sequence. It is used to isolate the DNA making up a human gene and to cut bacterial plasmid DNA with the same enzyme, forming complementary sticky ends.
The matching ends allow the human gene to join with the plasmid DNA. DNA ligase joins the DNA to form a recombinant plasmid containing the human gene.
Transfer, multiply and express the gene
The recombinant plasmid is inserted into bacteria. The bacteria containing recombinant plasmids multiply, increasing the number of gene copies. The human gene is expressed in bacteria, which make the human protein.
The syllabus does not require specific details of how recombinant plasmids enter the bacteria. Keep the sequence clear: cut gene and plasmid with the same restriction enzyme, join with ligase, transfer the plasmid, multiply bacteria and express the gene.
Pause and explain
Why are the same restriction enzymes used on the gene DNA and plasmid?
Worked example
Put these steps in order: bacterial gene expression, ligase joins DNA, bacteria multiply, plasmid and human gene cut with the same restriction enzyme, recombinant plasmid enters bacteria.
Show the worked solution
- Joining happens after DNA has matching ends.
- Transfer precedes bacterial multiplication and expression.
Answer Cut the human gene and plasmid with the same restriction enzyme; ligase joins them into a recombinant plasmid; insert the plasmid into bacteria; bacteria multiply; the gene is expressed to make the human protein.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Outline the steps from cutting the human gene and plasmid to making a human protein in bacteria.
Give me a hint
Keep the operations in order.
Compare my reasoning
- Same restriction enzyme cuts the gene and plasmid, forming complementary sticky ends.
- Ligase joins them; the recombinant plasmid enters bacteria, which multiply and express the gene.
Restriction enzymes cut the human gene and bacterial plasmid with the same enzyme, forming complementary sticky ends. DNA ligase joins them into a recombinant plasmid. The plasmid is inserted into bacteria; bacteria multiply and express the human gene to make the protein.
Look for these in your work
- Correct order
- Enzyme roles accurate
State the roles of restriction enzymes and DNA ligase.
Give me a hint
One cuts DNA; the other joins DNA.
Compare my reasoning
- Restriction enzymes cut at specific sequences and form sticky ends.
- DNA ligase joins the human gene and plasmid DNA.
Restriction enzymes cut the human gene DNA and plasmid DNA with matching sticky ends. DNA ligase joins the gene into the plasmid to form recombinant DNA.
Look for these in your work
- Both enzymes named
- Roles distinguished
Why must bacteria containing the recombinant plasmid multiply before large-scale protein production?
Give me a hint
Link cell multiplication with the number of gene copies and producing cells.
Compare my reasoning
- Multiplication increases the number of bacteria carrying the plasmid.
- More such cells can express the human gene.
Multiplication increases the number of bacteria carrying the recombinant plasmid, so many cells can express the human gene and produce the protein.
Look for these in your work
- Plasmid-carrying cells identified
- Multiplication linked to production
Common mistakes
- Using different restriction enzymes for the two DNA sources in the taught outline
- Saying DNA ligase cuts DNA
- Putting protein production before gene expression
What can you explain now?
What does DNA ligase do in the taught genetic-modification process?
Compare with the explanation
Joins the human gene to plasmid DNA
Ligase joins DNA to form a recombinant plasmid.
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Make it stick
Sequence the gene-transfer process and distinguish restriction enzymes, DNA ligase, plasmid transfer and gene expression.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.