polypeptides are produced by bacteria and cut dna at specific points.
polypeptides are produced by bacteria and cut dna at specific points.
what are produced by bacteria and cut dna at specific points?
polypeptides
the gene of interest must be separated from the extracted dna. if the sequence is not known then a common method is to break the dna up with a random digestion method. this is usually accomplished using restriction enzymes (enzymes that cut dna). a partial restriction digest cuts only some of the restriction sites, resulting in overlapping dna fragment segments. the dna fragments are put into individual plasmid vectors and grown inside bacteria. once in the bacteria the plasmid is copied as the bacteria divides. to determine if a useful gene is present on a particular fragment the dna library is screened for the desired phenotype. if the phenotype is detected then it is possible that the bacteria contains the target gene.
genetic engineering techniques
nucleases are enzymes that cut dna strands by catalyzing the hydrolysis of the phosphodiester bonds. nucleases that hydrolyse nucleotides from the ends of dna strands are called exonucleases, while endonucleases cut within strands. the most frequently used nucleases in molecular biology are the restriction endonucleases, which cut dna at specific sequences. for instance, the ecorv enzyme shown to the left recognizes the 6-base sequence 5′-gatatc-3′ and makes a cut at the horizontal line. in nature, these enzymes protect bacteria against phage infection by digesting the phage dna when it enters the bacterial cell, acting as part of the restriction modification system. in technology, these sequence-specific nucleases are used in molecular cloning and dna fingerprinting.
dna