Partial digest in restriction mapping

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Discussion Overview

The discussion revolves around the concept of restriction mapping in molecular biology, specifically focusing on how to determine whether DNA has been completely digested by restriction enzymes. The participants explore the implications of fragment sizes resulting from digestion and how these can indicate partial digestion.

Discussion Character

  • Homework-related
  • Technical explanation

Main Points Raised

  • One participant suggests that if the sum of the fragment sizes is greater than the size of the original DNA, it indicates a partial digest.
  • Another participant provides an example with a 10 kb linear DNA cut into 4 kb and 6 kb pieces, questioning the expected bands in both complete and incomplete digests.
  • A later reply confirms that in a complete digest, only the 4 kb and 6 kb fragments would be present, while an incomplete digest would also show the original 10 kb piece, leading to a sum that appears larger than expected.
  • It is noted that incomplete digestion results in "extra" bands, contributing to a total size greater than the original DNA fragment.

Areas of Agreement / Disagreement

Participants appear to agree on the relationship between fragment sizes and the completeness of digestion, but the discussion does not resolve all aspects of the implications or the reasoning behind these observations.

Contextual Notes

The discussion does not clarify certain assumptions regarding the conditions of the digestion process or the specific enzymes used, which may affect the outcomes discussed.

Mycelium
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Homework Statement


The question:
Scientists need to take precautions when they carry out restriction mapping. They need to make sure that the enzyme they have used has completely digested the DNA. One check they may carry out is to add the sizes of the fragments together. How could scientists use this information to show that the DNA has not been completely digested?

Homework Equations

The Attempt at a Solution


I know that it would be indicative of a partial digest if the sum of the fragments was greater than the size of the original fragment, but I don't understand why it would be so?
 
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Well, let's say you have a 10 kb linear DNA that gets cut into a 4 kb and 6 kb piece. What bands do you expect to see in a complete digest, and what is the sum of the sizes of the bands? If the digest is incomplete, what fragments do you expect to see, and what is the sum of the sizes of the bands?
 
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Ygggdrasil said:
Well, let's say you have a 10 kb linear DNA that gets cut into a 4 kb and 6 kb piece. What bands do you expect to see in a complete digest, and what is the sum of the sizes of the bands? If the digest is incomplete, what fragments do you expect to see, and what is the sum of the sizes of the bands?
Okay, I think I get it. So if it was complete, you would see only 4kb and 6kb fragments. If incomplete, there would be 10kb pieces along with the 4 and 6 kB pieces so it would seem as though you had a 20kb piece originally?
 
Yup. Incomplete digestion essentially gives "extra" bands that will make the sum of the sizes of the bands larger than the original piece of DNA.
 
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