Biotechnology for Health (Biomedical Innovations)

Unit 6: Problem 6: Molecular Biology in ActionBI 6.1Biomedical Innovation: transformation & gel electrophoresis

Run a transformation with selection

Move a plasmid into bacteria, then use a selective plate to tell which cells actually took it up.

Builds on (2 levels back)inferred · med confidence

What a plasmid is: Transformation moves a small ring of DNA (a plasmid) into bacteria, so you need to know a plasmid is a separate loop of DNA that can carry an added gene.
Bacteria grow into colonies: One cell divides many times into a visible dot (a colony), so counting colonies is how you count successful cells.

Prerequisites are inferred: pending teacher review.

Re-learn the skill with worked practice and clear examples.

Transformation moves a plasmid into bacteria; a selective plate then only lets cells that took the plasmid grow, so the colonies are your transformed cells.

Step 1: Add the plasmid

Transformation is the step where bacteria take up an outside plasmid. Not every cell succeeds: most do not.

Step 2: Let the plate select

A selective plate holds an agent the plasmid protects against. Cells WITH the plasmid survive and grow; cells WITHOUT it die. That filtering is called selection.

Step 3: Read the result

Each colony on the selective plate grew from one cell that took up the plasmid. Counting colonies counts your successful transformations.

Practice

You transform bacteria, then spread them on a selective plate (it contains an agent only the plasmid protects against). The next day you see colonies. What grew?

Reviewed

A.Every cell you spread, whether or not it took up the plasmid
B.Only the cells that took up the plasmid
C.Only cells that did NOT take up the plasmid
D.The plasmid molecules themselves, not cells

Show the worked solution ▾

Answer: B. Only the cells that took up the plasmid

Step 1: Name the filter: The selective plate kills cells that lack the plasmid's protection.
Step 2: Decide who survives: Only cells carrying the plasmid are protected, so only those grow into colonies.

Why it's right: Selection means only the protected (transformed) cells survive, so the colonies are cells that took up the plasmid.

Why the others miss:

A: If every cell grew, the plate would not be selecting for anything.
C: Cells without the plasmid have no protection and die on a selective plate.
D: Plasmids are DNA molecules; they do not grow into visible colonies on their own.

Aligned to BI 6.1: transformation & selection · reading level ~grade 9

Where you'd see this

A researcher only keeps colonies from the selective plate, because those are the cells that actually carry the new gene.

Careers that use this

Genetic Engineer: Uses selection to pull out only the bacteria that took up an engineered plasmid.

Video library

Watch: Run a transformation with selection

Bacteria Transformation

Teach Engineering · ~3 min

Guided notes

Fill these in as you work through the lesson.

Big idea: Transformation pushes a plasmid into bacteria. A selective plate only lets the cells that took up the plasmid grow, so the colonies you count are the transformed cells.

Key terms: write the meaning

Transformation (getting outside DNA into a cell):
Selection (a plate that filters who survives):
Colony (a visible dot from one cell):
Plasmid (the small DNA ring you add):

The rule

On a selective plate, only cells that took up the can grow, so each you count came from one cell.

Check yourself

On a plate with the selecting agent, why do untransformed cells fail to grow?
If you see zero colonies on the selective plate, what does that tell you about your transformation?
Why do scientists also grow some cells on a plate with NO selecting agent?

Work one example

You spread transformed cells on a plate that contains the selecting agent and count 24 dots the next day. Explain what those 24 dots are and why a cell that did not take up the plasmid is not one of them.