genetic of viruses

• Genome of viruses varies according to the type of virus, which may be DNA or RNA in nature and single- or double-stranded.
• The Lytic Cycle is a reproductive cycle of phages, such as T4 phages.
• Retroviruses, such as HIV, are an example of animal viruses with a reproductive cycle known as Retroviruses.
• The Lambda Phage is an example of a phage with a Lytic Cycle reproductive cycle.
• Reverse transcriptase is used to convert mRNA into DNA, which is then used as a template to form viral DNA.
• RNA viruses can possess either positive-sense RNA (i.e identical to viral mRNA and thus can be immediately translated) or negative-sense RNA (i.e complementary to viral mRNA and thus must be converted to positive-sense RNA by RNA polymerase before translation).
• Viruses undergo different reproductive cycles, with some bacteriophages, such as T4 phage, reproducing via lytic cycle while others, like lambda phage, reproducing via lytic and/or lysogenic cycles.
• Animal viruses such as influenza virus and HIV reproduce through other mechanisms.
• Genome of influenza virus varies according to the subtype of influenza virus.
• Genome of human immunodeficiency virus (HIV) varies according to the clade of HIV.
• A phage-encoded lysozyme is synthesised within the host cell, which breaks down the bacterial peptidoglycan, causing osmotic lysis and release of the intact new bacteriophages, leading to destruction of the host cell.
• T4 phage is a lytic reproductive cycle that results in the death of the bacterial host by causing lysis of the bacterial host cell.
• T4 phage specifically infects Escherichia coli (E.coli), which is a gram negative bacteria.
• T4 phages are considered to be virulent phages as they reproduce only by a lytic cycle.
• Replication - Replication of phage DNA & Synthesis of phage proteins.
• Penetration - Injection of phage DNA.
• Up to 50 to 200 phages may be produced and released per infected bacterium.
• Release - causing lysis of bacterium host cell.
• Maturation - spontaneous assembly of viral particles.
• The lytic life cycle of T4 phage typically consists of the following: Adsorption (or attachment) - attachment of T4 phages onto specific receptor sites on surface of host.
• Genome of viruses is inherited through outlining the reproductive cycles of bacteriophages that reproduce via lytic cycle only, bacteriophages that reproduce via lytic and lysogenic cycles, enveloped viruses, and retroviruses.
• An isolated virus is unable to reproduce and can only infect an appropriate host organism.
• Viruses can only reproduce within a host cell.
• Each type of virus can infect and parasitize only a limited range of host cells, known as its host range.
• In 1897, Martinus Beijerinck ruled out the possibility that the disease was due to a filterable toxin produced by a bacterium by demonstrating that the infectious agent could reproduce.
• The ability of infection and causing disease was undiluted even after several transfers from plant to plant.
• The sap from one generation of plants could be used to infect a second generation of plants that could infect subsequent generations.
• Variation in viral genomes arises due to antigenic shift and antigenic drift.
• Viruses are derived from the Latin word, virus, which refers to poison and other noxious substances.
• Molecular biology was largely born in the laboratories of microbiologists studying viruses that infect bacteria.
• Adolf Mayer discovered the cause of tobacco mosaic disease in 1883, which stunts tobacco plant growth and mottles plant leaves.
• Dimitri Ivanowsky demonstrated in 1893 that the sap from infected tobacco leaves was still infectious even after passing it through a filter designed to remove bacteria.
• Despite his belief that it could be very small bacteria or toxins produced by bacteria that caused the disease, Dimitri Ivanowsky was the first to identify viruses.
• Host specificity depends on the evolution of recognition systems of the viruses.
• Once inside, the viral genome takes control of its host, reprogramming the cell to make copies of the viral nucleic acid and synthesize proteins encoded by the viral genome.
• When a temperate phage infects a bacterium, it can either replicate by means of the lytic life cycle and cause lysis of host bacterium or it can incorporate its DNA into the bacterium’s DNA and become prophage in the lysogenic life cycle.
• A simplified version of a viral infection begins when the genome of the virus enters the host cell.
• The viral nucleic acid molecules and capsomeres then self-assemble into new viral particles and exit the cell via budding, exocytosis or through lysis of the host cell.
• Some viruses have a broad enough host range to infect several species while others infect only a single species.
• Most viruses of multicellular eukaryotes infect specific tissues.