Recombinant DNA flow
Tue, Dec 1, 2026 · Week 15 · Genetics of Disease (Medical Interventions)
Today's goal: Trace how recombinant DNA lets cells manufacture a useful human protein.
This is a model of the work you should turn in today. Use it to check your own: match the structure and the level of detail, do not copy it. Your data and wording should be your own.
Parallel case, not your own diagram: the same flow for chymosin, the cheese-making enzyme, so the gene and the product are different from yours.
- Step 1, Get a gene the microbe can read: the chymosin gene comes from calf stomach cells, and a gene cut straight out of a cow chromosome carries introns a bacterium cannot remove. So the gene is copied as cDNA from the calf's chymosin mRNA, which has no introns, and it is given ends that match the enzyme used in Step 2.
- Step 2, Cut the plasmid: a restriction enzyme opens the bacterial plasmid and leaves sticky ends that match the ends on the gene.
- Step 3, Insert the gene: DNA ligase seals the gene into the plasmid, behind a bacterial promoter. The result is recombinant DNA, meaning DNA combined from two sources.
- Step 4, Transform the host: E. coli takes up the recombinant plasmid, and an antibiotic-resistance gene on the plasmid lets only transformed cells grow on the selection plate.
- Step 5, Make the protein: the bacterium transcribes the calf gene into mRNA and translates it into prochymosin, which is purified and activated into chymosin. Grow the culture and the bacteria make it in bulk.
Named product: chymosin, used to curdle milk for cheese. Before recombinant chymosin was approved in 1990, cheese makers took it from the stomach lining of calves.
Why a bacterium can read a calf gene: the genetic code is nearly universal, so the codons mean the same amino acids inside the bacterial cell. What a bacterium cannot do is splice out introns, which is why the gene goes in without them.
(Tip: draw the gene and the opened plasmid with matching sticky ends, since matching ends are the part graders look for.)
This model shows the level of evidence and organization needed to complete: Models the recombinant-DNA flow diagram on a parallel case: a labeled sequence showing a plasmid cut open, a gene from another organism inserted, a host cell transformed, and the named product made.
- Date and label the entry.
- Record the procedure, observation, or design decision clearly.
- End with what the evidence means and the next step.
Keep the structure. Replace the question, facts, measurements, and evidence. Then recheck units, vocabulary, and whether the conclusion goes beyond the evidence.
Also due today: Attach the diagram to your PLTW tracker, and turn it in in Schoology under the Unit 4 Recombinant DNA Flow assignment.
Turn in: Labeled recombinant-DNA flow diagram showing plasmid cutting, gene insertion, host-cell transformation, and a named protein product.
Go to Schoology to turn this in.
Submit one PDF. Schoology attaches your name to your upload; on the page itself, write your period and code. Name the file: FirstName LastName - Assignment Title - YYYY-MM-DD.pdf.
Open Schoology PDF upload helpIf you cannot get in, see Mr. Mendoza. Do not skip the work.
Claim ceiling: Today's evidence supports a classroom claim about recombinant DNA flow. It cannot prove causation, diagnose a real patient, or justify action outside this room.
One exam-style question that uses exactly what you practiced today. Try it before you reveal the answer, then read why each choice is right or wrong.
Tap an answer to see the full explanation. Nothing is recorded or graded.
It builds this reusable test skill: Sequencing the steps of making recombinant DNA.
- Name the concept or data pattern being tested.
- Cross out choices that violate that rule or the evidence.
- Justify the best remaining choice before checking the answer.