# How to solve restriction mapping problems?

• foldedelephants
In summary, the following data was collected:-Four enzymes were used to digest a piece of DNA that was 1000bp long-Each enzyme was used in isolation and in different combinations-The digests were 223, 227, 400, 150 bp-The size of the fragments produced by each enzyme when used alone and in combination is shown-There is no 450 base-pair sized chunk in the E+B digest
foldedelephants

## Homework Statement

A piece of linear DNA 1000bp long is completely digested by four enzymes, E, B, P, and S.
We are given the sizes of fragments (in bp) produced when each of the enzymes are used in isolation, and when they are used in different combinations:
E : 227, 773
B : 150, 450, 400
P : 400, 600
S : 206, 794
E + B : 223, 227, 400, 150
E + P : 227, 373, 400
B + S : 56, 150, 344, 450
P + S : 194, 206, 600

Not applicable

## The Attempt at a Solution

I understand that with E + B, for example, as 227, 400, and 150 bp are present, enzyme B must have cut the 773 fragment into three pieces, 223, 400, and 150. I really don't know how to piece this information together to make a restriction map, it doesn't make any sense to me.

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Hello foldy,

The problem statement is missing a question. Could it be it's incomplete ?
You seem to know what a restriction map is; could you elucidate ?

In the mean time I notice E+B has no 450 base-pair sized chunks. Could that be the consequence of one of the restrictions ?

BvU said:
Hello foldy,

The problem statement is missing a question. Could it be it's incomplete ?
You seem to know what a restriction map is; could you elucidate ?

In the mean time I notice E+B has no 450 base-pair sized chunks. Could that be the consequence of one of the restrictions ?
Yes, apologies for that, there isn't a question as such; I need to construct a restriction map from this data. My question is how do I do this?
A restriction map shows all the positions of the restriction sites in a piece of DNA, which has information such as the length of the fragments and the enzyme responsible for each restriction site.
Yes, I think that with the E + B combination, enzyme E must have cut into the 450 fragment, dividing it into 227 bp and 223 bp. I'm just not sure how to go from recognising points such as these to constructing the full restriction map.

Can you try drawing the different possible maps that are consistent with the E, B, and E+B digests? After you have those possibilities, consider the other two restriction enzymes and use those data to try ruling out some of the maps.

## 1. How do I determine the size of a DNA fragment in restriction mapping?

In order to determine the size of a DNA fragment, you will need to compare it to a known size standard. This can be achieved by running a gel electrophoresis, where the DNA fragments will separate based on their size. By comparing the distance the fragment traveled on the gel to the distance the known size standard traveled, you can estimate the size of the fragment.

## 2. What is the purpose of using restriction enzymes in restriction mapping?

Restriction enzymes are used in restriction mapping to cut the DNA at specific locations. This allows for the identification and mapping of restriction sites within the DNA sequence. It also allows for the comparison of different DNA samples, as the presence or absence of certain restriction sites can indicate genetic differences.

## 3. How do I know which restriction enzyme to use in restriction mapping?

The choice of restriction enzyme will depend on the specific DNA sequence being analyzed. Generally, the DNA sequence will be compared to a database of known restriction enzyme recognition sites to determine the most suitable enzyme. It is important to consider factors such as the efficiency of the enzyme and the desired fragment sizes when selecting an enzyme for restriction mapping.

## 4. What is the difference between single and double digestion in restriction mapping?

In single digestion, only one restriction enzyme is used to cut the DNA sample. This results in a single set of fragments with varying sizes. In double digestion, two different restriction enzymes are used, resulting in two sets of fragments that can be compared to each other. This allows for a more accurate and detailed mapping of restriction sites within the DNA sequence.

## 5. Can restriction mapping be used to identify mutations in DNA?

Yes, restriction mapping can be used to identify mutations in DNA. Mutations can alter the sequence of restriction sites, resulting in changes in the size and number of fragments produced during digestion. By comparing the restriction map of a mutated DNA sample to that of a normal sample, mutations can be identified and located within the DNA sequence.

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