Restriction enzymes are a special class of proteins that cut DNA at specific sites and have become an indispensable tool in molecular biology. Restriction enzymes, also known as endonucleases, recognize specific sequences of DNA base pairs and cut or chemically separate the DNA at that site. The specific sequence of DNA recognized by a restriction enzyme is called a restriction site.

These unique enzymes occur naturally in some bacteria and act to protect them from invading viruses. Viruses called bacteriophages, phages for short, attack bacteria by inserting their genetic material into the bacterial cell. The phage commandeers the bacterial cell, replicating rapidly until the bacterial cell lyses and releases more phages to carry out the same infection process in neighboring cells. However, if the bacterial strain has restriction enzymes that recognize restriction sites on the invading phage nucleic acid, then enzymes can destroy the invading genetic material by digesting and inactivating the phage genes. Bacterial cells protect their own DNA from being self-digested by modifying certain nitrogen bases along their genome, this prevents their restriction enzymes from recognizing and digesting their own sequences.


In this experiment, you will

  • Perform agarose gel electrophoresis using three different predigested samples of lambda DNA and uncut lambda DNA.
  • Stain the gel.
  • Document and examine gel results with an imaging system.
  • Construct a standard curve and determine the size of the DNA fragments from the gel using Logger Pro.