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Name: Honey
Status: Other
Grade:  Other
Location: N/A
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 in nature, or how the bacteria scientists use in a lab are made to be resistant 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 ring.

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.

Ethan Greenblatt
Ph.D. Candidate
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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