1 Chapter 4: recombinant DNA Restriction enzyme analysis Cloning in E. coli plasmids Transformation Biomedical application
Dec 17, 2015
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Chapter 4: recombinant DNA
Restriction enzyme analysis
Cloning in E. coli plasmids
Transformation
Biomedical application
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Restriction enzymes
• Restriction enzymes cut double-strand DNA at specific recognition sequences which are often 4-6 base pair palindromes = 5’-3’ sequence is identical on both DNA strands
• Many restriction enzymes cut the two DNA strands at different points which generates complementary single-strand ends = sticky ends (others = blunt ends)
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BamHI (from B. amyloliquefaciens ) recognizes GGATCC and cuts between the G’s on both strands
Restriction enzymes
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DNA fragments of different size (e.g.
restriction fragments) can be separated
according to their size by gel electrophoresis:
• agarose gel electrophoresis (300 bp - 15 kb)
• polyacrylamide gel electrophoresis (1-500 b)
=PAGE
Restriction enzymes
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Recombinant DNA
• Sticky ends formed
by restriction enzymes
permit circularization or
combinations of DNA
restriction fragment(s)
by complementary
base pairing
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• A new combination of DNA can be made by combining restriction fragments
• Complementary sticky ends can be covalently linked with DNA ligase to form recombinant DNA
• Blunt end DNA fragments (for example generated by PCR) can also be ligated (but less efficiently)
Recombinant DNA
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• A vector is a replicating unit that can be
opened to insert another DNA fragment
• Often plasmids are used as vector in bacteria
A plasmid is a small self-replicating circular
DNA molecule found in bacteria
Recombinant DNA
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Plasmid vectors have
• an origin of replication
• a selectable marker gene (often an antibiotic resistance)
• a cloning site or multicloning site (MCS)
Recombinant DNA
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Transformation by heat shock or electroshock
bacteriumtransformation
Plasmid replication
Replicating bacteria form colony
Recombinant DNA
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Selection
Plate bacteria on selective medium
Select for presence of marker
Medium containing antibiotic
R
Recombinant DNA
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+
=Vector
DNA fragments
Recombinant DNA molecules
+=
Recombinant DNA
DNA 1DNA 2DNA 3In reality only one or up to millions of fragments
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Cloning = purification
Transform plasmids into bacteria: a cell will replicate only one plasmid type
Plate bacteria to form colonies
Recombinant DNA
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Methods of genetic manipulation are named:• Recombinant DNA technology• Genetic engineering• Gene cloning or gene technology
Applications include:• Isolation of specific genes• Production of specific proteins
Genetic engineering
• GMO = genetically modified organism, GMM = genetically modified micro-organisme
• Genetic modification = targeted modification of a genetic characteristic of an organism
transgenic organisme
Genetic engineering
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Biomedical applications
• Recombinant DNA technology is used to produce large amounts of medically important proteins such as blood clotting factors, insulin,…. In either bacteria, fungi, animal cells, whole animals or plants
• DNA probes detect mutant genes in hereditary diseases (DNA diagnostics)
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• A chimeric gene is constructed of parts of different genes
• An eukaryotic gene can only be expressed in bacteria when provided with the correct expression signals (and vice versa)
• Example: human insulin production in bacteria
Bacterial promoterCoding region human insulin gene
Bacterial terminator
Genetic engineering