An important example of a phenotype is that
of antibiotic resistance. This animation will demonstrate how the genotype of
a bacterial cell determines whether its phenotype will be survival in the presence
of the antibiotic ampicillin, a drug similar to penicillin. A bacterium that
contains a plasmid carrying the gene for ampicillin resistance, denoted as AmpR, is shown here in cross-section. Since
the gene encodes the enzyme beta-lactamase, it is also
referred to as bla. The particles on the
outside of the cell wall are ampicillin molecules. To survive in the presence
of the antibiotic, the cell first transcribes the AmpR
gene into messenger RNA, or mRNA, represented by the blue wavy line. The mRNA
is then translated into a special type of protein called an enzyme, which is
called beta lactamase, and is shown as a green
molecule. Beta lactamase goes to the periplasm of the bacterium, between the inner and outer
membranes, and binds to molecules of ampicillin before they enter the cell.
In order to be active and to the kill bacteria, ampicillin molecules must
contain an intact chemical structure known as a beta-lactam
ring. However, beta-lactamase breaks this ring,
thus inactivating the antibiotic and allowing the cell to survive. Since this
bacterial cell contains a gene for ampicillin resistance, its genotype is AmpR and therefore its phenotype is the
ability to grow in presence of ampicillin.
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