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Viruses (viruses replicate only in host cells (one virus is just a package…
Viruses
viruses replicate only in host cells
viruses lack metabolic enzymes and equipment for making proteins
one virus is just a package set of genes in transit from one host cell to another
the host range of a virus is the limited amount of host species that a virus can infect
measles virus has a small host range, and west nile virus has a large host range
a viral infection begins when a virus binds to a host cell and the viral genome makes its way inside
T-even phages use their elaborate tail apparatus to inject DNA into bacterium; other viruses are taken up by endocytosis, enveloped viruses fuse the viral envelope with the host's plasma embrane
when the viral genome is inside of the host, the proteins it encodes reprogram the cell to copy the viral genome and manufacture viral proteins
the host provides nucleotides for making viral genomes , enzymes, ribosomes, tRNAs, amino acids, ATP, and other components needed for making the viral proteins
the lytic cycle: phage replicative cycle that culminates in death of the host cell; last stage of infection where the bacterium breaks open and releases the phages that were produced within the cell
a virulent phage is a phage that replicates only by a lytic cycle
lysogenic cycle: allows replication of the phage genome without destroying the host
temperate phages are capable of using both modes of replicating within bacterium
replicative cycles of animal viruses: viral genome is double or singled stranded DNA or RNA, presence or absence of membranous envelopes
they use the envelope to enter the host cell, capsid and viral genome enter cell, synthesize complementary RNA strands, new copies of RNA are made using complementary RNA strands, vesicles transport glycoproteins to plasma membrane, capsid assembles around viral genome molecule
Viruses and prions are formidable pathogens in animals and plants
a prion is a protein that causes a number of degenerate brain ideas in various animal species.
mad cow disease, scrapie in sheep
viral diseases in animals
they can be treated with vaccines- harmless derivative of a pathogen that stimulates the immune system to mount defenses against the harmful pathogen
vaccines can prevent some illnesses but they most illnesses can't be cured once viral infections occur
smallpox is treated by vaccine
viral diseases in plants
they can be seen as bleached leaves or brown spots on leaves and fruit, stunted growth, and damaged flowers or roots
tobacco mosaic disease is a viral plant disease
they spread by two major routes
horizontal transmission: plant is infected from an external source of the virus
a plant becomes more susceptible to viral infections if it has been damaged by wind, injury, or herbivores because the invading virus has to get past the plant's outer protective layer to infect it
vertical transmission: a plant inherits a viral infection from a parent
occurs in asexual propagation or in sexual reproduction via infected seeds
emerging viruses are viruses that suddenly become apparent
HIV, ebola, chikungunya, and influeza are emerging viruses
three processes contribute to the emergence of viral diseases
mutation of existing viruses
RNA viruses have a high rate of mutation because viral RNA polymerases don't correct error in replicating their RNA genomes
dissemination of a viral disease from a small isolated human population
AIDS existed for decades but was unnoticed before it spread around the world
the spread of existing viruses from other animals
animals that harbor and can transmit a certain virus but are generally unaffected by it are natural reservoirs for this virus
H1N1 virus (swine flu)
an epidemic is a widespread outbreak
a pandemic is a global epidemic
a virus is an infectious particle consisting of mostly genes packed in a protein coat
a virus consists of a nucleic acid surrounded by a protein coat, and some are surrounded by a membranous envelope
viral genomes consist of either double stranded DNA, single stranded DNA, double stranded RNA, or single stranded RNA
the nucleic acid in the genome determines if a virus is a DNA virus or an RNA virus
the genome is usually organized a single linear or circular molecule of nucleic acid, but some genomes consist of multiple molecules of nucleic acids
a capsid is the protein shell enclosing the viral genome that can be rod-shaped, polyhedral, or more complex in shape.
they are built from protein subunits called capsomeres
a viral envelope is a membranous envelope that surrounds the capsids of influenza viruses and other viruses found in animals
they are derived from the membranes of the host cell and contain host cell phospholipids and membrane proteins and proteins and glycoproteins of viral origin
bacteriophages are viruses that infect bacteria where many of the most complex capsids are found
T-even phages' capsids have elongated icoshedral heads enclosing their DNA
there is a protein tail attached to the head with fibers that the phage uses to attach to bacterial cells
tobacco mosaic virus has a helical capsid surrounding a single helical RNA molecule with the overall shape of a rigid rod
adenoviruses have an icohedral capsid with a protein spike at each vertex (capsid contains double-stranded DNA)
influenza viruses have an outer envelope studded with glycoprotein spikes that contains 8 double-helical RNA-protein complexes, each associated with a viral polymerase
bacteriophage T4 has a complex capsid consisting of an icoshedral head and a tail apparatus, and has double-stranded DNA enclosed in its head
"a kind of borrowed life", somewhere in between life forms and chemicals
viruses are smaller and simpler than eukaryotes an prokaryotes
they lack the structures and metabolic machinery found in a cell