Restriction enzyme: An enzyme from bacteria that can recognize specific base sequences in DNA and cut the DNA at that site (the restriction site). A restriction enzyme acts as a biochemical scissors. Bacteria use restriction enzymes to defend against bacterial viruses called bacteriophages (or phage).

Bacteria protect their DNA by modifying their own recognition sequences, usually by adding methyl (CH3) molecules to nucleotides in the recognition sequences and then relying on the restriction enzymes’ capacity to recognize and cleave only unmethylated recognition sequences.

When a virus injects its genes, these so-called restriction enzymes shred them into genetic confetti, so that they can’t take over the cell.

Digestion of vector DNA using (preferably) two restriction enzymes. This reduces the background of non-recombinants due to self-ligation of the vector (especially when a single site was used for cloning).

Restriction enzyme, also called restriction endonuclease, a protein produced by bacteria that cleaves DNA at specific sites along the molecule. In the bacterial cell, restriction enzymes cleave foreign DNA, thus eliminating infecting organisms.

Generating Recombinant DNA During the process, restriction enzymes will digest or cut the DNA from both the bacteria and the other organism, resulting in DNA fragments with compatible ends, reports the Medicine Encyclopedia. These ends are then pasted together through the use of another enzyme or ligase.

Restriction enzyme function in the natural world is to defend bacteria against specific viruses called bacteriophages. These viruses attack bacteria by injecting viral RNA or DNA into a bacterial plasmid (small, purple ring in the below image) and replicating there.

DNA restriction enzymes break DNA strands at specific sites based on the nucleic acid sequence. For known mutations the affected DNA sequence can be amplified (see later) prior to RFLP analysis (or by single-nucleotide extension if the mutation does not alter a restriction enzyme cleavage site).

Sources. Bacterial species are the major source of commercial restriction enzymes. These enzymes serve to defend the bacterial cells from invasion by foreign DNA, such as nucleic acid sequences used by viruses to replicate themselves inside a host cell.

BamHI (from Bacillus amyloliquefaciens) is a type II restriction endonuclease, having the capacity for recognizing short sequences (6 bp) of DNA and specifically cleaving them at a target site. This allows the DNA to maintain its normal B-DNA conformation without distorting to facilitate enzyme binding.

Additional Information: The EcoRI is a restriction enzyme that creates four nucleotide sticky ends with the end of 5′. The enzyme cuts at the recognition site of G/AATTC which has a complementary sequence of CTTAA/G. Here “/” represents the phosphodiester bond that the enzyme breaks in the DNA molecule.

GAATTC

Recognition Sequences

The enzyme cleaves the DNA at the positions where the GGCC sequence is found. The cleavage occurs between the second and the third nucleotides (G and C). The resulting DNA fragments are known as restriction fragments. HaeIII cuts both strands of DNA in the same location, yielding restriction fragments with blunt ends.

The EcoRI cut sites are not directly across from each other on the DNA molecule. When EcoRI cuts a DNA molecule, it therefore leaves single stranded “tails” on the new ends (see the example just given). This type of end has been called a “sticky end” because it is easy to rejoin it to complementary sticky ends.

EcoRI creates 4 nucleotide sticky ends with 5′ end overhangs of AATT. The nucleic acid recognition sequence where the enzyme cuts is G↓AATTC, which has a palindromic, complementary sequence of CTTAA↓G….

Ecori full form: The Eco portion of the enzyme’s name comes from the species where it was isolated – “E” stands for “Escherichia” and “co” stands for “coli” – while the R stands for the specific strain, in this case RY13, and the I stands for “first ever enzyme extracted from this strain.”

Because sticky ends find each other faster due to their attraction for each other, the process of ligation requires less human DNA and less plasmid DNA. The blunt ends of DNA and plasmids are less likely to find each other, and thus ligation of blunt ends requires that more DNA is put into the test tube.

informal an unpleasant finish or death (esp in the phrase come to or meet a sticky end)

Definition. noun, plural: sticky ends. (molecular biology) A fragment of DNA (often produced by a staggered cut on the DNA using restriction enzymes) in which the terminal portion has a stretch of unpaired nucleotides, and the strands are not of the same length.

Sticky ends therefore facilitate the ligation of diverse segments of DNA, and allow the formation of novel DNA constructs.

There are overhanging stretches called sticky ends on each strand (Figure 11.1). These are named so because they form hydrogen bonds with their complementary cut counterparts. This stickiness of the ends facilitates the action of the enzyme DNA ligase.

Sticky ends are produced by restriction enzymes. These enzymes cut the strand of DNA a little away from the centre of the palindrome sites but between the same two bases on the opposite strands. This stickiness of the ends facilitates the action of the enzyme DNA ligase.

This leaves single stranded portions at the ends. These overhanging stretches on each strand are called sticky ends. They form hydrogen bonds with their complimentary counterparts and facilitate the action of DNA ligase enzyme.

A restriction enzyme is an enzyme isolated from bacteria that cuts DNA molecules at specific sequences. The isolation of these enzymes was critical to the development of recombinant DNA (rDNA) technology and genetic engineering.

(ii) Endonuclease − It is a type of restriction enzyme that makes a cut within the DNA at a specific site. (c) Chitinase − Chitinase is a class of enzymes used for the degradation of chitin, which forms a major component of the fungal cell wall.

Restriction enzymes

When selecting restriction enzymes, you want to choose enzymes that:

1. Flank your insert, but do not cut within your insert.
2. Are in the desired location in your recipient plasmid (usually in the Multiple Cloning Site (MCS)), but do not cut elsewhere on the plasmid.