Fill the gel chamber with buffer, not water
The same buffer appears twice in this workflow, once inside the gel and once around it. Learn what the dissolved salts are doing and why distilled water leaves your bands standing still.
- Dissolved salts let a liquid carry current: Pure water conducts very poorly. Dissolve salts in it and the liquid can carry a current, which is what makes a buffer different from water for this purpose.
- A circuit needs an unbroken path: Current has to be able to travel from one electrode to the other. Anything that breaks the path stops the run, whether it is a lifted gel or an empty chamber.
Prerequisites are inferred: pending teacher review.
Re-learn the skill with worked practice and clear examples.
Now get the level right, and see what an interrupted path does.
How much buffer goes into the chamber?
Reviewed- A.Right to the very top of the chamber, so nothing can dry out
- B.Enough to wet the tray, leaving the gel surface dry for loading
- C.Enough that the buffer just covers the surface of the gel
- D.Half the depth of the gel, so the wells stay above the liquid
Show the worked solution ▾
Answer: C. Enough that the buffer just covers the surface of the gel
- Step 1: Ask what has to be in contact: The whole gel, including both ends, and the liquid at each electrode.
- Step 2: Ask what more would buy: Nothing useful, and an overfilled chamber is harder to move without spilling.
Why it's right: Covering the gel puts every part of it in contact with the liquid that carries the current and stops the surface drying during the run. Going far beyond that adds spill risk without adding anything.
- A: A chamber filled to the brim spills when it is moved or when the cover goes on, and none of that extra liquid improves the run.
- B: A dry gel surface means the gel is not in the path at all, and the samples are loaded under the liquid rather than onto a dry surface.
- D: Wells above the liquid cannot be loaded the way this procedure loads them, and the top of the gel would dry out during the run.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
A gel goes into the chamber with an air bubble under one end of the tray, which lifts that end clear of the liquid. What does that do to the run?
Reviewed- A.It cools that end of the gel, which makes the bands in those lanes sharper
- B.Nothing at all, so long as the wells themselves are covered
- C.It speeds the run up, since there is less liquid to travel through
- D.That end is out of the path, so those lanes move unevenly or not at all
Show the worked solution ▾
Answer: D. That end is out of the path, so those lanes move unevenly or not at all
- Step 1: Trace the path: Electrode, buffer, gel, buffer, electrode. It has to be continuous.
- Step 2: Find the break: A lifted end is a gap in that path, and a gap stops current going through.
Why it's right: The current has to travel through an unbroken path of liquid and gel. A lifted end is a gap in that path, so the part of the gel beyond it is not being driven the way the rest is.
- A: Sharp bands come from even conditions across the gel. An end sitting in air is the opposite of even.
- B: Covered wells matter for loading, but the run needs the whole gel connected, not just the end the samples went into.
- C: Less liquid does not mean an easier journey. The fragments travel through the gel, and a broken path slows or stops them rather than helping.
Aligned to Handling, Preparation, Storage and Disposal · reading level ~grade 9
- A student checks the buffer level against the gel surface instead of against a line on the box.
Fill these in as you work through the lesson.
- Buffer (a salt solution, used inside the gel and around it):
- Current (what moves the fragments, carried by the buffer):
- Submerged (how much of the gel the buffer has to cover):
- Distilled water (almost no dissolved salts, so almost no current):
Make the gel with diluted and fill the chamber with the same . Fill until it just the gel, because both ends of the gel have to be in contact with the liquid that carries the .
- Say what the dissolved salts in the buffer are for.
- Predict what a chamber filled with distilled water does to a run.
- Explain what goes wrong if one end of the tray sits above the liquid.
You dilute the buffer once and use it twice: some of it becomes the gel, and the rest goes into the chamber until it just covers the gel surface. Both ends of the gel are wet, the path from one electrode to the other is unbroken, and the run can start.