Summary
Summary Gene Technology
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Biology A level revision notes on genetic technology
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Genetic technologyThe aim of genetic engineering is to remove a gene from one organism and transfer it
to another so that the gene is expressed in the new host. The organism that now
expresses the new gene is known as transgenic or genetically modified. Unlike
selective breeding where whole sets of genes are involved, genetic engineering often
results in the transfer of a single gene.
Recombinant DNA: DNA made by joining pieces from two or more different sources
Overview of gene transfer
1. The required gene is identified. It may be cut from a chromosome, made from
mRNA by reverse transcription or synthesised from nucleotides
2. Multiple copies of the gene are made using the technique known as the
polymerase chain reaction
3. The gene is inserted into a vector eg. Plasmids, viruses and liposomes, which
delivers the gene to the cells of the organism.
4. The vector takes the gene into the cells
5. The cells that have the new gene are identified and cloned
The genetic engineer needs:
Enzymes, such as restriction endonucleases, ligase and reverse transcriptase
Vectors, including plasmids and viruses
Genes coding for easily identifiable substances that can be used as markers
Restriction enzymes
These enzymes cut the sugar-phosphate backbone of DNA at specific places within
the molecule and their role in bacteria is to restrict a viral infection. Each restriction
enzyme binds to a target site on DNA and cuts at that site. Bacterial DNA is protected
from the attack by chemical markers or by not having the target sites. These sites are
specific sequences of bases and they read the same in both directions (palindrome).
Sticky ends are short lengths of unpaired bases and they can easily form hydrogen
bonds with complimentary sequences of bases on other pieces of DNA cut with the
same restriction enzyme.
Vectors
Inserting the gene into a plasmid vector:
One type of vector is a plasmid, a small, circular piece of double stranded DNA. The
bacteria containing the plasmids have their cell walls broken down with enzymes.
The bacteria are then spun in a centrifuge to separate large and small chromosomes.
The circular DNA is cut open using a restriction enzyme, the same one that cut out
the gene so the sticky ends are complimentary.
The enzyme DNA ligase is used to link together the sugar-phosphate backbones of
the DNA molecule and the plasmid, producing recombinant DNA. Plasmids can be
made artificially and the pUC group have:
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