Biotechnology for Health (Biomedical Innovations)

Unit 6: Problem 6: Molecular Biology in ActionBI 6.1Biomedical Innovation: recombinant DNA & cloning

Plan a recombinant-DNA workflow

Put the steps of building recombinant DNA in order: cut with an enzyme, join with ligase, carry it in a plasmid.

Builds on (2 levels back)inferred · high confidence

DNA is a molecule with a sequence: You must know DNA is a chain of bases with a specific order before you can see why an enzyme cuts at one exact spot.
Enzymes act on specific targets: Restriction enzymes and ligase are enzymes; knowing enzymes do one specific job explains why each tool has one role in the workflow.

Prerequisites are inferred: pending teacher review.

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

The workflow is: cut the DNA with a restriction enzyme at a specific site, then use ligase to join the cut gene into a plasmid that carries it into a cell.

Step 1: Cut at a chosen site

A restriction enzyme (molecular scissors) recognizes one short DNA pattern and cuts there. It cuts the gene you want out of one DNA source and opens the plasmid at a matching site.

Step 2: Join the pieces

Ligase (molecular glue) seals the cut gene into the opened plasmid, making one combined circle. This combined molecule is the recombinant DNA.

Step 3: Carry it into a cell

A plasmid is a small circular piece of DNA that acts as a vector: a carrier. A cell can take up the plasmid and then copy the gene along with it.

Step 4: See the figure

Match each numbered step in the diagram to its tool: scissors at the cut, glue at the join, the circle as the carrier.

Practice

A team wants to insert a gene into a plasmid so bacteria can carry it. The numbered diagram shows the workflow. Which order of tools is correct?

Reviewed

Three-step workflow. Step 1: a straight DNA strand with scissors at a marked site. Step 2: an open circular plasmid with the gene fragment and a glue drop between their ends. Step 3: a closed circular plasmid now containing the gene.

A.Ligase to cut, then restriction enzyme to join, then plasmid to carry
B.Restriction enzyme to cut, then ligase to join, then plasmid to carry
C.Plasmid to cut, then ligase to carry, then restriction enzyme to join
D.Restriction enzyme to carry, then plasmid to cut, then ligase to join

Show the worked solution ▾

Answer: B. Restriction enzyme to cut, then ligase to join, then plasmid to carry

Step 1: Name the cutter: The scissors in Step 1 are the restriction enzyme, which cuts at a specific site.
Step 2: Name the joiner: The glue in Step 2 is ligase, which seals the gene into the opened circle.
Step 3: Name the carrier: The closed circle in Step 3 is the plasmid, which carries the gene into a cell.

Why it's right: Cut first with the restriction enzyme, join with ligase, then let the plasmid carry the recombinant DNA into a cell.

Why the others miss:

A: Ligase joins, it does not cut, so it cannot be the first step.
C: A plasmid is a carrier, not a cutter, and ligase does not carry DNA.
D: A restriction enzyme cuts, it does not carry, and a plasmid is not a cutter.

Aligned to BI 6.1: recombinant-DNA workflow order · reading level ~grade 9

Where you'd see this

A cloning protocol lists 'digest, ligate, transform': those three words are exactly cut, join, and carry-into-a-cell.

Careers that use this

Molecular Biologist: Designs each cloning experiment by choosing which restriction enzyme cuts where and how ligase joins the gene into the plasmid.

Video library

Watch: Plan a recombinant-DNA workflow

Animation 27.1 Basic principle of recombinant DNA technology

Oxford Mastering Biology 牛津基礎生物學 · ~2 min

Guided notes

Fill these in as you work through the lesson.

Big idea: To build recombinant DNA you cut DNA at a chosen spot with a restriction enzyme, then use ligase to paste the piece into a plasmid that will carry it into a cell.

Key terms: write the meaning

Recombinant DNA (DNA built from two different sources):
Restriction enzyme (the molecular scissors):
Ligase (the molecular glue):
Plasmid (the small circular carrier):

The rule

First a restriction enzyme the DNA at a specific site, then joins the gene into a circular that carries it into a cell.

Check yourself

Which tool makes the cut, and which tool makes the join?
Why does a restriction enzyme have to cut at a specific site instead of anywhere?
What job does the plasmid do that the enzyme and ligase cannot?

Work one example

You want to put a human insulin gene into bacteria. List the workflow steps in order and name the tool used at each step (cutting, joining, carrying).