SDS-PAGE gel results
Fri, Dec 11, 2026 · Week 16 · Genetics of Disease (Medical Interventions)
Today's goal: Read an SDS-PAGE gel, a gel that sorts proteins by size, to judge the size and purity of your isolated 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 practice gel, not today's: a practice enzyme expected near 45 kDa.
How I read it: the marker lane holds proteins of known size, so it is my ruler. Smaller proteins travel farther from the well.
Reading:
- Marker bands at 100, 75, 50, 37 and 25 kDa. My target band sits between the 50 and 37 kDa bands, closer to 50, so I estimate about 45 kDa.
- Band counts: crude lysate, 9 bands; flow-through, 8 bands with only a faint band at 45; wash, 2 faint bands; elution, 1 strong band at about 45 kDa plus 1 faint band near 70 kDa.
- Most pure lane: the elution lane, because it has one dominant band at the expected size and only one faint extra band.
QC statement: the column enriched the enzyme but did not make it pure. One faint extra band remains, and a Coomassie-stained gel cannot show proteins below about 100 ng per band, so 'one strong band' describes what this stain can see, not proof that nothing else is in the tube.
| Lane | Bands seen | Reading |
|---|---|---|
| Marker | 100, 75, 50, 37, 25 kDa | the ruler |
| Crude lysate | 9 bands | everything the cells made |
| Flow-through | 8 bands, faint at 45 | unbound proteins |
| Wash | 2 faint bands | loosely bound proteins |
| Elution | strong at about 45, faint near 70 | most pure, enriched not pure |
This model shows the level of evidence and organization needed to complete: Models the gel reading on a parallel practice gel for a different protein: marker lane labeled, size estimated against the ladder, bands counted by lane, the most pure lane named, and a QC statement that states its own limit.
- Name the variables and include units.
- Enter observations without changing the raw values.
- Check labels, calculations, and patterns before interpreting the data.
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 your annotated gel reading to your Unit 4 PLTW tracker and submit it in Schoology.
Turn in: Annotated SDS-PAGE gel image with labeled marker lane, estimated protein size, band counts by fraction, most-pure fraction identified, and a QC statement.
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 SDS-PAGE gel results. 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: Judging protein purity from an SDS-PAGE band pattern.
- 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.