BI226 Chapter Notes - Chapter 9: Plasmid, Genomic Library, Recombinant Dna
Document Summary
A restriction enzyme recognizes specific base sequences on genomes, and severs ea(cid:272)h e(cid:374)d"s phosphodieste(cid:396) (cid:271)o(cid:374)ds, i(cid:374) a p(cid:396)o(cid:272)ess k(cid:374)o(cid:449)(cid:374) as digestion: the fragments that result from this process are known as restriction fragments. Restriction enzymes originate in bacteria: protect cells from viral infection, the selective addition of a methyl group (- ch3) to their own restriction recognition sites allows for bacteria to shield their genomes from being digested. Restriction enzymes target sequences usually 4-8 base pairs long. When cut, enzymes produce sticky or blunt ends. If cut in a zig-zag, sticky ends are produced. Considered sticky because they are free to base pair with a complimentary sequence of the dna of any organism cut by the same enzyme. Usually the base pairs are palindromic, meaning they are identical when read in the (cid:1009)" to (cid:1007)" di(cid:396)e(cid:272)tio(cid:374) Different restriction enzymes recognize different sequences, so depending on how small or large the fragment needs to be a different restriction enzyme is used.
