Frontiers of GeneticsCh. 13Ms. Levensailor
Biologists manipulate DNA
Biotechnology: The use of organisms to perform practical tasks for humans.◦Analyze and manipulate genomes at the
molecular level. Called DNA technology. Use E. Coli and bacteria for models of gene
manipulation. Why bacteria?
◦Unique way of creating genetic recombination.
Lederberg &Tatum
Demonstrated that 2 bacteria can form a tunnel like connection.◦Pass genes to each other.◦Results in new combinations of genes.
2 other methods:◦Viruses can carry bacterial genes from one
bacterial cell to another.◦Take up loose pieces of DNA from their
surroundings.
Recominant DNA Technology
Scientists make use of the way bacteria can transfer and recombine DNA.◦Combine genes from different sources into a
single DNA molecule. Can be from different species.
Engineering Bacteria
Bacteria contain plasmids:◦A small circular DNA molecule.◦Separate from the larger bacterial
chromosome.◦Carry a number of genes.◦Can make copies of itself.
Plasmid replication:◦One copy can pass from one bacterial cell to
another.◦Results in gene sharing.
Beneficial Results of Gene Sharing
Bacteria can carry plasmids containing genes that make them resistant to antibiotics.◦Plasmid copies of this gene are spread to the
bacterial population.Result of this:
◦Increasing variety of bacteria that are resistant to current antibiotics.
How can humans benefit?
Biologists use plasmids to move pieces of DNA into bacteria.◦Example: genes useful for products
Process of Gene Cloning:◦1. Plasmid is removed from bacterial cell.◦2. Desired gene (from any kind of cell) is inserted
into the plasmid.◦3. Plasmid is now a combination of original DNA and
new DNA (Recombinant DNA).◦4. It is now put back into a bacterial cell, and
replication occurs many times.
Genetically Engineered Bacterial Cell
Plasmids: carriers of genetic information.
Cutting and Pasting DNA
How do we remove a gene from one DNA molecule and put it into another?◦A piece of DNA containing the desired gene
must be “cut”. RESTRICTION ENZYME Naturally found in bacteria and protect against
intruding DNA from other organisms. Chop up the foreign DNA into small pieces. Bacturium’s DNA is protected chemically from
being chopped up by its own restriction enzymes.
Restriction Enzymes
Recognize specific short nucleotide sequences in DNA molecules.
Cuts at sugar-phosphate bonds in DNA backbone.
Most make staggered cuts.◦Leaves single stranded DNA hanging off the
ends of the fragments.◦“Sticky Ends” are available to bind to any
sequence that is complementary to it.
Pasting DNA
Can be used to recombine DNA.“Pastes” the sticky ends together.
◦Repairs DNA backbone.
Cloning Recombinant DNA
We want to insertProtein V-gene.
Libraries of Cloned Genes
Cloning recombinant DNA results in many different clones.◦Each containing different portions of the source
DNA.◦Results in many genes being cloned in addition
to the target gene.Genomic Library:
◦Complete collection of cloned DNA fragments from an organism.
Identifying Specific Genes with Probes
How do we find a specific gene in the genomic library?◦1. We must know at least part of the gene’s
nucleotide sequence.◦Example:
Protein V contains sequence TAGGCT. Biologists use nucleotides labeled with radioactive
isotopes to build a complementary single strand. Called a nucleic acid probe.
Identifying Specific Genes with Probes
2. We heat the DNA to separate the 2 strands.
3. Nucleic acid probe is mixed in with the single strands.
Identifying Specific Genes with Probes
4. Probe tags the correct DNA portion by pairing with the complementary sequence in the Protein-V gene.
5. Biologists use a radioactive marker to identify the bacterial cells with the desired gene.
Uses of Bacterial Plasmids to clone genes
Bacterium
Bacterialchromosome
Plasmid
1 Plasmidisolated
3Gene insertedinto plasmid
2 DNAisolated
Cell containing geneof interest
DNAGene ofinterest
Recombinant DNA(plasmid)
4Plasmid put intobacterial cell
Recombinantbacterium
5Cell multiplies withgene of interest
Copies of proteinCopies of gene
Clone of cellsGene for pestresistanceinserted intoplants
Gene used to alter bacteriafor cleaning up toxic waste
Protein used to dissolve bloodclots in heart attack therapy
Protein used tomake snow format highertemperature
Top Related