Restriction enzymes are called molecular scissors because of their ability to cut DNA molecules at specific sequences. They are also known as restriction endonucleases and are produced naturally by bacteria as a defense mechanism against foreign DNA, such as those from viruses.

Mechanism of Action
Restriction enzymes recognize a specific sequence of nucleotides, called a recognition site, on the DNA molecule. Once they recognize their target sequence, they cut the DNA molecule at specific points, creating two fragments, which can then be separated and analyzed.

Types of Restriction Enzymes
There are different types of restriction enzymes, categorized according to their mode of action. For example, Type II restriction enzymes are the most commonly used and are known for their ability to cut DNA molecules at specific, palindromic sequences. Type I and III restriction enzymes cut DNA at random sites and require ATP to function.

Applications
Restriction enzymes have a wide range of applications in molecular biology, including DNA cloning, DNA fingerprinting, and genetic engineering. They are used to create recombinant DNA molecules, which can be used to study gene function and expression, as well as for the production of pharmaceuticals, vaccines, and genetically modified organisms.

Conclusion
In summary, restriction enzymes are called molecular scissors because of their ability to cut DNA molecules at specific sequences. They are an important tool in molecular biology and have numerous applications in research, medicine, and industry.