Microbiology Flashcards
Viruses
Viruses are tiny infectious agents, much smaller than bacteria. In its basic form, a virus consists of a protein coat, called a capsid, and from one to several hundred genes in the form of DNA or RNA inside the capsid. Most animal viruses surround themselves with a lipid-rich envelope either borrowed from the membrane of their host cell or synthesized in the host cell cytoplasm.
- Viral infection begins when a virus absorbs to a specific glycoprotein on the host.
- Next, the nucleic acid of the virus penetrates into the cell.
- Once inside the cell there are two possible paths: **lysogenic infection **or lytic infection.
Lytic and Lysogenic Infection
In Lytic infection, the virus commandeers the cell’s reproducitive machinery and begins reproducing new viruses. The cell may fill with new viruses until it lyses, or it may release the new viruses one at a time in a reverse endocytotic process. A virus that following a lytic cycle is called a virulent virus.
In a Lysogenic infection, the viral DNA is incorporated into the host genome, or, if the virus is an RNA virus, DNA is reverse-transcribed from RNA and then incorporated into the host cell genome. A virus in a lysogenic cycle is called a temperate virus. The infected cells may lay dormant until actived by stress, UV light, or carcinogens.
Plus-Strand and Minus-Strand RNA Viruses
Plus-strand RNA indicates that proteins can be directly translated from the RNA. Enveloped plus-strand RNA viruses include retroviruses. Retroviruses carry the enzyme reverse transcriptase in order to create DNA from its RNA. This DNA can then be incorporated into the genome of the host cell.
Minus-strand RNA is complement to mRNA and must be transcribed to plus-RNA before being translated.
Prokaryotes
Prokaryotes do not have a membrane bound nucleus. They also have no complex, membrane-bound organelles at all. The two major shapes are cocci (round) and bacilli (rod shaped). spirilla is a helically shaped bacteria.
