Protein expression
Tue, Dec 8, 2026 · Week 16 · Genetics of Disease (Medical Interventions)
Today's goal: Explain how a host cell expresses the inserted gene to produce the target 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 today's data: a practice E. coli culture carries an inserted gene for an enzyme that turns a colorless test chemical blue. The gene sits behind a promoter that switches on only when the inducer IPTG is added.
What expression means: expression is the cell reading the inserted gene and using it to build the protein.
Tracing the steps:
1. Transcription: RNA polymerase binds the promoter in front of the inserted gene and copies the gene into mRNA. With no IPTG, the promoter stays switched off and little mRNA is made.
2. Translation: ribosomes read the mRNA codons and join amino acids into the enzyme, which folds into its working shape.
Two conditions that change yield in this parallel case:
- Inducer: with IPTG added the promoter is switched on, so far more mRNA and enzyme are made.
- Aeration: a flask shaken fast has more oxygen, so the cells grow denser and make more enzyme in total than a still flask.
Evidence expression worked (parallel practice data): the induced, shaken culture turned the test chemical deep blue in 10 minutes; the culture without IPTG stayed nearly colorless. The color is made by the enzyme, so the difference between the two cultures is evidence that the inserted gene was expressed only when switched on.
How to use this: trace your own inserted gene the same way, and take your evidence from the practice expression data on today's page.
This model shows the level of evidence and organization needed to complete: Models the expression notes on a parallel practice culture that makes a different reporter protein: the transcription and translation trace, two conditions that change yield, and one piece of expression evidence read from practice data.
- 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: Add your expression notes to your Unit 4 PLTW tracker and submit in Schoology.
Turn in: Annotated notes tracing transcription and translation of the inserted gene, two yield-affecting conditions, and one piece of expression evidence from the practice expression data on this page.
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 protein expression. 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: Explaining gene expression and recognizing evidence that it succeeded.
- 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.