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Chapter 19 (Virus (Capsid (The protein shell enclosing the viral genome is…
Chapter 19
Virus
Virus is an infectious particle consisting of little more than genes packaged in a protein coat.
Latin roots for virus mean "poison." Virus is a non living thing.
Capsid
The protein shell enclosing the viral genome is called capsid.
Capsid maybe rod-shaped, polyhedral, or more complex in shape. Built from large number of protein subunits called capsomeres.
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Adenovirus, which infect the respiratory tracts of animals, have 252 identical protein molecules arranged in a polyhedral capsid with 10 triangular facets- an icosahedron; thus, these and other similarly shaped viruses are referred to as icosahedral viruses.
Viral envelopes
Derived from the membranes of the host cell, contain host cell phospholipids and membrane protein. They also contain protein and glycoproteins of viral origin.
Retroviruses
The RNA animal with the most complicated replicative are the retroviruses. These viruses have an enzyme called reverse transcriptase.
HIV and retroviruses are enveloped viruses that contain two identical molecules of single-stranded RNA and two molecules of reverse transcriptase.
Bacteriophages
Most complex capsids are found among the viruses that bacteria, called bacteriophages.
Provirus
The integrated viral DNA viral DNA, called a provirus, never leaves the host's genome, remaining a permanent resident of the cell.
Vaccine
A vaccine is a harmless derivative of pathogen that stimulates the immune system to mount defenses against the harmful pathogen.
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prions
Proteins called prions appear to cause a number of degenerative brain disease in various animal species.
Evolution
1) The envelope glycoproteins enable the virus to bind to specific receptor on certain white blood cells.
2) The virus fuses with the cell's plasma membrane. The capsid proteins are removed, releasing the viral proteins and RNA.
3) Reverse transcriptase catalyzes the synthesis of DNA strand complementary to the viral RNA,
4) Reverse transcriptase catalyzes the synthesis of a second DNA strand complementary to the first.
5) The double stranded DNA is incorporated as a provirus into the cell's DNA.
6) Proviral genes are transcribed into RNA molecules, which serve as genomes for progeny viruses and as mRNA for translation into viral protein.
7) The viral proteins include capsid proteins and reverse transcriptase (made in the cyotsol)and envelope glycoproteins (made in ER).
8) Vesicles transport the glycoproteins to the cell's plasma membrane.
9) Capsids are assembled around viral genomes and reverse transcriptase molecules.
10) New viruses, with viral envelope glycoproteins, bud from the host cell.
Host range
Each particular virus can infect cells of only a limited number of host species, called host range of the virus. Virus usually identify host cells by "low-and-key" fit between viral surface proteins and specific receptor molecules on the outside of cells.
Lytic cycle
A phage replicative cycle culminates in death of the host cell is known as a lytic cycle. The terms refers to the last stage of infection, during which the bacterium lyses (breaks open) and release the phages that were produced within the cell..
Lysogenic cycle
Many phages coexist with them in a state called lysogeny. The lytic cycle, which kills the host cell, the lysogenic cycle.
Virulent phage
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Phages capable of using both modes of replicating within a bacterium are called temperate phages. A single infected cell can quickly give rise to a large population of bacteria carrying the virus in prophage form. This mechanism enables viruses to propagate without killing the host cells on which they depend.
Prophage
When integrated into the bacterial chromosome in this way, the viral DNA is known as a prophage.
Lysogenic
The term lysogenicsignifies that prophages are capable of generating active phages that lyse their host cells.