shoving, and scrambling in all directions. But this image doesnât really do justice to the interior of an E. coli cell. An airport terminal, after all, is a rigid and stable structure that exists in two dimensions (or if we take into account the stratification of arriving and departing as well as domestic and international passengers, and so on, we could attribute to it a slightly larger fractional dimensionality such as 2.1), whereas the cytoplasm is unquestionably a dense three-dimensional throbbing blob. Inside it, however, everything careens relentlessly toward self-replication, for within the space of about thirty minutes, the cell manages to duplicate with extreme precision each and every one of its component parts: its proteins, lipid molecules, even its own genome. And at the end of the process, the cell pinches itself in two, giving birth to a daughter cell clone, which will reproduce itself in another half hour.
The role of E. coli in genetic engineering stems from its ability to reproduce itself with its characteristic high speed and great fidelity. According to a standard account (which is probably correct), genetic engineering in the modern sense was born in 1972, when two biologists met for a late-night snack at a delicatessen near Waikiki beach in Hawaii. Stanford University medical professor Stanley Cohen and biochemist Herbert Boyer, of the University of CaliforniaâSan Francisco, were in Honolulu to attend a conference on plasmids, the circular strands of DNA found in the cytoplasm of bacteria. Plasmids can be replicated independently of the cellâs chromosomes.
At the conference, Cohen announced that he could insert plasmid DNA into E. coli and have the bacterium propagate and clone the plasmid. Boyer described his work with EcoRI, an enzyme (named after and isolated from E. coli ) that could cut DNA at specific, predefined sites along the length of the molecule. Later that night the two scientists realized that by combining their respective innovations they could splice together fragments of two different plasmids, producing recombinant (mechanically changed) DNA, and then get the bacterium to mass-produce whatever it was that the engineered plasmid coded for.
But as correct as that account may be, Cohen and Boyer were not the worldâs first (nor even the most successful) genetic engineers. That distinction belongs to viruses, particularly bacteriophages (such as the T4 phage, which looks like a lunar landing module straight from the Apollo program).
A virus is essentially a string of DNA or RNA wrapped in a protein coating. It replicates by inserting its genome into a fully fledged cell, which proceeds to treat this new and foreign set of raw genes as if it were its own original genetic material. Uninfected cells use nucleic acids primarily to make proteins: a molecule of RNA polymerase (an enzyme) unzips a section of double-stranded DNA, reads off its genetic information, and constructs a complementary strand of mRNA (messenger RNA), in a process called transcription. The mRNA is in turn read by ribosomes, along with some other molecular machines, which collectively string together amino acids in the order prescribed by the mRNA, in a process called translation. Since a protein is nothing but a long string of amino acids, when the translation is complete, so is the protein.
Infection by a virus changes the picture entirely. For an E. coli bacterium, an attack by a phage virus initiates a cascade of violence and destruction equal to anything offered up by horror fiction. The phages descend on the bacteriumâs outer membrane like a swarm of bees and forcefully insert their DNA through the cell membrane and into the cytoplasm. The viral DNA invaders now sabotage the cellâs normal transcription and translation of the its own genes, and redirect those processes on themselves. At that point, the viral genome has taken over the organism, and some minutes later, with its own enzymes
The role of E. coli in genetic engineering stems from its ability to reproduce itself with its characteristic high speed and great fidelity. According to a standard account (which is probably correct), genetic engineering in the modern sense was born in 1972, when two biologists met for a late-night snack at a delicatessen near Waikiki beach in Hawaii. Stanford University medical professor Stanley Cohen and biochemist Herbert Boyer, of the University of CaliforniaâSan Francisco, were in Honolulu to attend a conference on plasmids, the circular strands of DNA found in the cytoplasm of bacteria. Plasmids can be replicated independently of the cellâs chromosomes.
At the conference, Cohen announced that he could insert plasmid DNA into E. coli and have the bacterium propagate and clone the plasmid. Boyer described his work with EcoRI, an enzyme (named after and isolated from E. coli ) that could cut DNA at specific, predefined sites along the length of the molecule. Later that night the two scientists realized that by combining their respective innovations they could splice together fragments of two different plasmids, producing recombinant (mechanically changed) DNA, and then get the bacterium to mass-produce whatever it was that the engineered plasmid coded for.
But as correct as that account may be, Cohen and Boyer were not the worldâs first (nor even the most successful) genetic engineers. That distinction belongs to viruses, particularly bacteriophages (such as the T4 phage, which looks like a lunar landing module straight from the Apollo program).
A virus is essentially a string of DNA or RNA wrapped in a protein coating. It replicates by inserting its genome into a fully fledged cell, which proceeds to treat this new and foreign set of raw genes as if it were its own original genetic material. Uninfected cells use nucleic acids primarily to make proteins: a molecule of RNA polymerase (an enzyme) unzips a section of double-stranded DNA, reads off its genetic information, and constructs a complementary strand of mRNA (messenger RNA), in a process called transcription. The mRNA is in turn read by ribosomes, along with some other molecular machines, which collectively string together amino acids in the order prescribed by the mRNA, in a process called translation. Since a protein is nothing but a long string of amino acids, when the translation is complete, so is the protein.
Infection by a virus changes the picture entirely. For an E. coli bacterium, an attack by a phage virus initiates a cascade of violence and destruction equal to anything offered up by horror fiction. The phages descend on the bacteriumâs outer membrane like a swarm of bees and forcefully insert their DNA through the cell membrane and into the cytoplasm. The viral DNA invaders now sabotage the cellâs normal transcription and translation of the its own genes, and redirect those processes on themselves. At that point, the viral genome has taken over the organism, and some minutes later, with its own enzymes
Similar Books
