Restriction enzymes: A) act at the membrane to restrict the passage of certain molecules into the cell. B) are highly specialize
d ribonucleases that degrade mRNA soon after its synthesis. C) are sequence-specific DNA endonucleases. D) are very specific proteases that cleave peptides at only certain sequences. E) catalyze the addition of a certain amino acid to a specific tRNA. c The biological role of restriction enzymes is to: A) aid recombinant DNA research. B) degrade foreign DNA that enters a bacterium. C) make bacteria resistant to antibiotics. D) restrict the damage to DNA by ultraviolet light. E) restrict the size of DNA in certain bacteria.
Restriction enzymes represent a type enzyme capable of recognizing short nucleotide sequences to cut at specific restriction sites in the DNA, these sites are known as target DNA sequences. Some of the most commonly used restriction enzymes are <em>EcoRI</em>, <em>BamHI</em> and <em>HindIII</em>, isolated from <em>Escherichia coli</em>, <em>Bacillus amyloliquefaciens</em> and <em>Haemophilus influenza</em>, respectively. Restriction enzymes are endonucleases because these enzymes only cleave the phosphodiester bond within the DNA chain, conversely to exonucleases, which cleave nucleotides from the end of the polynucleotide DNA strand.
