A biologist wishes to take a useful gene found in pine trees and introduce it into some bacterial cells. Her experimental procedure is given below.

1. Use a restriction enzyme to cut a gene out of the pine tree DNA.
2. Use a restriction enzyme to cut open a plasmid.
3. Treat the plasmid with DNA ligase.
4. Mix the desired gene and plasmid together.
5. Introduce the plasmid into bacterial cells.
Which steps should be switched in the biologist's procedure?

A. 3 and 4
B. 1 and 3
C. 2 and 3
D. 4 and 5

option A

Explanation:

In carrying out these experimental procedure, the same restriction enzyme that is used to cut out the gene of interest should also be the same used for the cutting of the plasmid to generate sticky ends. Then the desired gene is inserted into the cut plasmid  then treatment with DNA ligase. Purified DNA ligase is utilized in gene cloning to join/ligate DNA molecules together forming a recombinant DNA. Thus, step 3 should be carried out after step 4.

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