Craig C. Freudenrich
Although they are made up of only single cells, bacteria perform many of the same processes that your body's cells perform. They have cell walls and cell membranes that separate their interiors from the outside world. They're not exactly like typical human cells, however. Bacteria are more complex in many ways and they have special capsules that regulate what materials can enter the cell walls to protect the bacteria. They reproduce, which involves making copies of their genetic information (DNA) and distributing that information to their offspring, or daughter cells. Bacterial cells make proteins, which do many things, including carrying out the numerous chemical reactions necessary for life. Protein synthesis involves making copies (ribonucleic acid, or RNA) of the instructions for specific proteins contained in DNA, gathering the building materials of proteins (amino acids) and assembling the proteins on scaffolding (ribosomes) according to the instructions. There are subtle differences in how bacterial proteins carry out chemical reactions, how ribosomes assemble the proteins and in how cells make the building blocks of DNA that antibiotics target; this also is why antibiotics don't kill your normal cells.
Antibiotics fight bacterial infections by either directly killing the bacterial cells (bactericidal) or by preventing their growth and reproduction (bacteriostatic). There are several major classes of antibiotics, broken down here by the processes they target:
- Interfering in cell walls or cell membranes. These antibiotics bind with proteins, fats or complex sugars that make up the structure of the cell wall or membrane. The cell wall weakens and the bacterial cell breaks open and dies. Antibiotic families of this type include penicillin, cephalosporin, carbapenem, monobactam and aminoglycoside.
- Interfering with DNA synthesis. Disrupting the process by which DNA is copied can lead to death or prevent reproduction. Different antibiotic families do this in different ways. Quinolones interfere with a protein that unwinds the DNA helix, which is necessary for copying DNA. In contrast, sulfonamides block the proteins that make the building blocks of DNA.
- Interfering with protein synthesis. These antibiotics bind to portions of bacterial ribosomes and prevent them from working. The cells die because they cannot make new proteins. Antibiotic families of this type include tetracycline, macrolide, telithromycin and aminoglycoside (which also blocks cell wall synthesis).
Antibiotics are designed to target bacteria, which are single-cell, living organisms. Sometimes, they get inside your body and make you sick by producing chemicals that cause harm. Antibiotics work like a selective poison, designed to kill a specific type of bacteria and avoid hurting your body's good cells. Depending on the bacteria they're targeting, antibiotics might go after a bacterium's ability to turn glucose into energy, for example, or they might hamper the way it builds a cell wall. Once they're stopped from doing what they do, bacteria can't reproduce and they die off.
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