Term Paper on "Biological Virus vs. Bacteria"

Term Paper 4 pages (1160 words) Sources: 0

[EXCERPT] . . . .

Virus v. Bacteria virus is a small particle that infects cells in biological organisms. Viruses are obligate intracellular parasites; they can reproduce only by invading and controlling other cells as they lack the cellular machinery for self-reproduction. The term virus usually refers to those particles which infect eukaryotes (multi-celled organisms and many single-celled organisms), while the term bacteriophage or phage is used to describe those infecting prokaryotes (bacteria and bacteria-like organisms).

Typically these particles carry a small amount of nucleic acid (either DNA or RNA) surrounded by some form of protective coat consisting of proteins, lipids, and glycoproteins. Importantly, viral genomes code not only for the proteins needed to package its genetic material, but also for proteins needed by the virus during lysogenic and lytic cycles, the reproductive cycles. A virus reproduces by causing a host cell that it infects to create copies of itself. When found outside of a host cell, viruses consist of genomic nucleic acid, either DNA or RNA (depicted as blue), surrounded by a protein coat, or capsid, with or without a glycoprotein envelope. There are three types of viruses: a bacterial virus, otherwise called a bacteriophage, an animal virus, and a retrovirus.

A phage (also called bacteriophage) is a small virus that infects only bacteria. Like viruses that infect eukaryotes, phages consist of an outer protein hull and the enclosed genetic material (which consists of double-stranded DNA in 95% of the phages known) of 5 to 650 kbp (kilo base pairs) with a length of 24 to 200 nm. The vast majority of phages (95%) have a tail to let them inject their genetic material into the host. Phages were discovered independently by Frederick Twort in 1915 and by Felix d'Herelle in 1917.

Phages infect only specific bacteria. Some phages are virulent, meaning that upon infecting a cell they immediately begin reproducing, and within a short time lyse (destroy) the cell, releasing new phages. Some phages (so-called temperate phages) can instead enter a relatively harmless state, either integrating their genetic material into the chromosomal DNA of the host bacterium, much like endogenous retroviruses in animals, or establishing themselves as plasmids. These endogenous phages, referred to as prophages, are then copied with every cell division together with the DNA of the host cell. They do not kill the cell, but monitor (via some proteins they code for) the status of their host. When the host cell shows signs of stress (meaning it might be about to die soon), the endogenous phages become active again and start their reproductive cycle, resulting in the lysis of the host cell. Sometimes, prophages even provide benefit to the host bacterium while they are dormant, by adding new functions to the bacterial genome, a phenomenon called lysogenic conversion. A famous example is the harmless Vibrio bacteria strain, which is turned into Vibrio cholerae by a phage, causing cholera.

Phages play an important role in molecular biology as cloning vectors to insert DNA into bacteria. Phage therapy has been used since the 1940s in the former Soviet Union as an alternative to antibiotics for treating bacterial infections, because killing bacteria is what phages do best. There is an extensive library of research into specific phages and their therapeutic uses in the Tbilisi Institute in Georgia. The development of bacterial strains that are resistant to multiple drugs has led Western medical researchers to re-evaluate phages as alternatives to the use of antibiotics.

Animal viruses replicate similarly to bacteriophages but there are modifications. If… READ MORE

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