1. Recognition Sequence:
* Specificity: Each restriction enzyme recognizes a specific, short sequence of DNA nucleotides. This sequence is typically 4-8 base pairs long and is called the recognition sequence or restriction site.
* Palindromic Nature: Many recognition sequences are palindromic, meaning they read the same backwards and forwards on the opposite DNA strands. For example, the enzyme EcoRI recognizes the sequence GAATTC, which is the same if you read it from right to left on the complementary strand (CTTAAG).
2. Cleavage:
* Cutting: Once the restriction enzyme finds its recognition sequence, it cuts the DNA molecule at a specific point within that sequence.
* Sticky Ends vs. Blunt Ends: The way a restriction enzyme cuts can produce either "sticky ends" or "blunt ends."
* Sticky Ends: The enzyme cuts the DNA strands at different positions, leaving short single-stranded overhangs that can base-pair with complementary overhangs from other DNA molecules cut with the same enzyme. This is useful for creating recombinant DNA molecules.
* Blunt Ends: The enzyme cuts both strands of DNA at the same position, leaving no overhangs.
In Summary:
The following factors determine how a restriction enzyme will cut DNA:
* The specific recognition sequence of the enzyme.
* The location of that sequence within the DNA molecule.
* The specific cleavage pattern of the enzyme (sticky ends vs. blunt ends).
Example:
The enzyme EcoRI cuts DNA at the sequence GAATTC, producing sticky ends. This means that it will cut any DNA molecule containing that sequence, and the resulting DNA fragments will have single-stranded overhangs that can be used for cloning or other genetic manipulations.
