he image below shows the restriction map of a circular plasmid that is 2981 base pairs long. The recognition sites of 3 restriction endonucleases are shown in base pairs from the origin of replication (0 bp). Link to image.
Links to an external site.

What is the size of the largest fragment in base pairs, produced by digestion of the plasmid with PvuI and Xmn1?

Question

he image below shows the restriction map of a circular plasmid that is 2981 base pairs long. The recognition sites of 3 restriction endonucleases are shown in base pairs from the origin of replication (0 bp). Link to image.
Links to an external site.

What is the size of the largest fragment in base pairs, produced by digestion of the plasmid with PvuI and Xmn1?

BlackTom AI · Accepted Answer

The question asks for the size of the largest fragment produced when the circular plasmid (2981 bp) is cut with PvuI and XmnI, given the locations of the restriction sites.

First, identify the cut sites from the image and text: PvuI sites at approximately 500 bp and 2413 bp, and XmnI site at approximately 2641 bp along the plasmid from the origin (0 bp).

Next, list the cut positions in ascending order around the circle: 500, 2413, 2641. Since the plasmid is circular, we consider the fragment sizes between consecutive cuts as we traverse the circle and then wrap around from the last cut back to the first cut.

Compute the distances between consecutive cut sites:
- From 500 to 2413: 2413 − 500 = 1913 bp
- From 2413 to 2641: 2641 − 2413 = 228 bp
- From 2641 back to 500 (wrapping around): (2981 − 2641) + 500 = 340 + 500 = 840 bp

Thus, the three resulting fragment sizes are 1913 bp, 228 bp, and 840 bp.

To answer the question, compare these fragment sizes to determine which is the largest. Among 1913, 228, and 840, the largest value is 1913 bp.

Note: If there were any ambiguity about site numbering (e.g., exact bp coordinates), the same approach—listing cut positions, computing inter-site distances around the circle, and selecting the maximum fragment size—would still apply. The key is to account for all cuts introduced by the enzymes and consider the circular nature of the plasmid when wrapping from the last cut back to the first.

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