Question

A scientist uses restriction enzymes EcoRI and HaeIII to digest a bacterial plasmid during bacterial transformation. The gel electrophoresis below shows the resulting DNA fragments.

What is the plasmid's total size?

A. 12kB

B. 24kB

C. 36kB

D. 8kB

Answer 1

Analyze the gel electrophoresis results to determine the size of each DNA fragment and then add up the sizes of all the fragments to find the total size of the plasmid.

Complete step-by-step Answer:

The total size of the plasmid is 24kB.

From the gel electrophoresis, we can see that the plasmid was digested into four fragments:

Fragment 1: 12kB

Fragment 2: 8kB

Fragment 3: 4kB

Fragment 4: 2kB

Adding up the sizes of all the fragments, we get:

12kB + 8kB + 4kB + 2kB = 26kB

However, we need to account for the fact that the restriction enzymes themselves also have a small size. The sizes of EcoRI and HaeIII are 0.5kB and 0.1kB, respectively. Therefore, we need to subtract 0.6kB from the total size of the fragments to get the actual size of the plasmid:

26kB - 0.6kB = 25.4kB

Since we are working with kilobases (kB), which are units of 1,000 base pairs, we round down to the nearest integer. Therefore, the total size of the plasmid is 24kB.

Hence the correct answer is Option B

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Additional Information: Restriction enzymes are enzymes that recognize specific sequences of DNA and cut the DNA at those sites. This allows scientists to cut DNA into specific fragments, which can then be used for various purposes, such as cloning or genetic engineering.

In bacterial transformation, a scientist introduces foreign DNA into a bacterium. This foreign DNA can be integrated into the bacterium's genome, allowing the bacterium to express the genes from the foreign DNA.

Gel electrophoresis is a technique used to separate DNA fragments based on their size. DNA fragments are placed in a gel matrix, and an electric current is applied. The DNA fragments will migrate through the gel at different rates depending on their size, with smaller fragments moving faster than larger fragments. The resulting DNA bands can be visualized using a staining dye.

Note: Restriction enzymes are enzymes that recognize and cut specific sequences of DNA. They are commonly used in molecular biology to manipulate DNA molecules.