Country: United States
Date: October 2006
How is a cell made ampicillin resistant?
You might be asking how a bacteria can become resistant to an antibiotic
nature, or how the bacteria scientists use in a lab are made to be
to certain antibiotics. The general idea is that in nature bacteria are
constantly exchanging genetic information. These genes in turn encode
proteins, and when a bacteria picks up a gene from the environment it can
start making new proteins.
In the lab you might have a gene that you want lots of copies of, and you
can use bacteria to do this work for you. You can add DNA to a bacteria in
the form of a plasmid, which is a circular piece of DNA that the bacteria
can copy when it divides. The basic idea is that you put holes into the
membrane of the bacteria by using chemicals or an electric potential, and
the DNA that you add will pass into the bacteria through these holes.
When you do this, you'll want a way to have only the bacteria that picked up
your DNA grow. By putting more than one gene on your plasmid, one for your
gene of choice and one that gives the bacteria antibiotic resistance, you
can select for the bacteria that picked up your DNA. This way, any bacteria
that grows in the presence of antibiotic has to have picked up the gene for
antibiotic resistance and therefore has to have the plasmid that you added
that also has your gene of choice. The bacteria can then go ahead and
divide numerous times and make lots and lots of copies of the DNA that you
added. In nature, if a bacteria has antibiotic resistance after having
picked up an antibiotic resistance gene and transfers this gene to another
bacteria, the other bacteria will now be resistant to your antibiotic.
The way that the antibiotic resistance to ampicillin works is that the
antibiotic ampicillin has a chemical structure known as a beta-lactam
The gene for antibiotic resistance makes a protein that breaks down any
chemical with a beta-lactam ring. This way the antibiotic around the
bacteria will get degraded and the bacteria will be able to survive.
Stanford Department of Chemistry
It depends what kind of cell you are speaking of-I'm pretty sure you are
talking about bacterial cells. The problem with resistance occurs when
there is a genetic mutation in the bacteria that makes it able to survive in
the presence of an antibiotic. For example, bacteria that are resistant to
penicillin have an enzyme that can break down the antibiotic.
Ampicillin resistance is usually a result of an enzyme (beta lactamase) that
breaks down the ampicillin. The origin of the enzyme in certain resistant
mutants is a mystery.
Ron Baker, Ph.D.
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Update: June 2012