Molecular scissors

Molecular scissors

How do our cells attack foreign DNA?

Cells have a unique mechanism to protect themselves from attack from viruses, fungi and bacteria. Inside each cell lies a group of special proteins, called restriction enzymes.

Restriction enzymes cut the DNA of a foreign organism into pieces before it has a chance to damage the cell. These enzymes are just like scissors. They can chop up a piece of DNA into very small pieces.


Restriction enzymes cut up foreign DNA before it has chance to attack the cell

Restriction enzymes don't just randomly attack foreign DNA. Instead their attack is more targeted.

How do restriction enzymes attack foreign DNA?

The blades of molecular scissors are not flat like regular scissors. Instead they have 'teeth' that fit specific chemical groups, called bases, on the DNA. Each blade has between 4-6 teeth.

A section of DNA can be made of several thousand bases. The scissors will only cut a certain section of the DNA, when its teeth are able to fit correctly between the bases. It's just like pieces fitting together in a jigsaw. The section of DNA that the scissors cut is called a 'recognition sequence' and is usually between 4-6 base pairs long.

Molecular scissors_99211748

Molecular scissors only cut a specific piece of DNA

Host DNA (DNA from the animal or plant that is being attacked) can also contain these recognition sequences.

In the host DNA, the bases making up the recognition sequence are chemically modified. The restriction enzyme can no longer fit correctly in between the bases. The host cell is protected from its own restriction enzymes.

Why are restriction enzymes important?

Our cells are attacked by foreign microorganisms, like viruses, every single day. If our cells didn't have restriction enzymes, they would be unable to protect themselves. We would waste a lot of our energy trying to recover from infections.

But that's not their only use. Molecular biologists have found a way to use restriction enzymes.

The biologists use restriction enzymes to cut sections of DNA from one organism and transfer it to another. This allows molecular biologists to create hybrid DNA that has the best properties of both organisms.

This technique has variety of uses in everyday medicine, including producing insulin, antibiotics and fuel. Scientists have also been using these enzymes to synthesise artificial DNA that can power the growth and replication of a simple cell in the laboratory.

One day this technology might help us make giant leaps in medicine and green fuel production.

Are DNA restriction sequences the same for all animals? Find out at Chop that DNA!

By Zara Mahmoud, ScienceBuz