Recombinant DNA in Bacteria Plasmids, Restriction Enzymes, Cloning DNA, Genetic Libraries, And Useful Products Created By Microorganisms Plasmids • Plasmids- a small, circular DNA molecule separate from the much larger bacterial chromosome • Plasmids are double stranded Plasmids (cont.) • Plasmids can replicate, just like normal DNA • When plasmids replicate, one copy can be passed from one bacteria cell to another • When Plasmids are shared, important information, such as an immunity to antibiotics, can be passed from a bacteria to any other species of bacteria Plasmids Can Help Humans • Scientists can use plasmids to move pieces of DNA into bacteria • These pieces of DNA can instruct bacteria to make important substances for humans, such as insulin Putting DNA into Plasmids • To place DNA in the plasmids, a plasmid is first removed from the bacteria cell • Next, a desired gene from any kind of cell, is inserted into the plasmid • This creates a recombinant plasmid, or a plasmid that contains original and new DNA • The recombinant plasmid is placed back into the bacteria cell, which copies it in a process called DNA Cloning Putting DNA into Plasmids (cont.) Restriction Enzymes • Restriction Enzymes- Enzymes that are used to cut DNA • Restriction Enzymes chop DNA into small pieces • Restriction Enzymes are found in bacteria, where they are used to chop up foreign DNA • Restriction Enzymes work by finding specific nucleotide segments and cutting the sugar phosphate backbone at certain places within those segments Restriction Enzymes (cont.) • Restriction Enzymes usually make staggered cuts • These staggered cuts leave single stranded areas called Sticky Ends, since they will bind to any complimentary sequence • An enzyme called DNA Ligase attaches the DNA fragments together Cutting and Pasting DNA Cloning Recombinant DNA • Biologists can place recombinant DNA in bacteria cells which can use the DNA to make large quantities of proteins that are useful to humans • Making enough DNA to be useful takes several steps Libraries of Cloned Genes • Genomic Library- a complete collection of cloned DNA fragments from an organism • The procedure of cloning DNA creates many different clones, each containing a different portion of the source DNA • The different recombinant plasmids contain the entire genome of the organism from which the DNA was derived Identifying Specific Genes With Probes • One way to find a specific gene is to use a radioactive probe, that is complementary to a piece of DNA with a known genotype • A biologist can use nucleotides labeled with a radioactive isotope to build a complementary single strand of DNA • The biologist uses chemicals or heat to separate the two strands, and the radioactive probe is mixed in Identifying Specific Genes With Probes (cont.) • Next, the probe tags the correct DNA portion by pairing with the complementary sequence • This way, the biologists can tell which bacteria cells contain the gene, and they allow those bacteria cells to multiply, producing the genes in large amounts Useful Products from Genetically Engineered Microorganisms • Bacteria can be given DNA to produce chemicals to clean up toxic waste sights • Bacteria can be used to mass produce useful chemicals • Bacteria can be used to make human insulin • It is also being used to create vaccines. Genes from viruses can be cloned in cells, which allows the cells to create large amounts of viral protein, which can be used to make the vaccines.
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