Chapter 13: Viruses

characteristics of viruses

- obligatory intracellular parasites: require living host cells to multiply
- contain DNA or RNA (never both)
- contain a protein coat
- no ribosomes
- no ATP generating mechanism

host range

the spectrum of host cells a virus can infect
- most viruses infect only specific types of cells in one host

bacteriophages

viruses that infect bacteria

through filters

how could the small size of viruses help researchers detect viruses before the invention of the electron microscope?

virion

complete, fully developed viral particle

capsid

protein coat made of capsomeres (subunits; individual units)

envelope

lipid, protein, and carbohydrate coating on some viruses

spikes

projections from outer surface; all envelopes have spikes, if it did not then it would not be able to infect anything

capsomeres

allows viruses to infect a host

viral species

a group of viruses sharing the same genetic information and ecological niche (host)
- descriptive common names are used for species
- subspecies are designated by a number

lytic cycle

- occurs when things are going bad
- phage causes lysis and death of the host cell

lysogenic cycle

- when things are going good
- phage DNA is incorporated in the host DNA
- phage conversion
- specialized transduction (phage is replicating and producing other genes)

attachment

phage attaches by the tail fibers to the host cell

penetration

phage lysozyme opens the cell wall; tail sheath contracts to force the tail core and DNA into the cell

biosynthesis

production of phage DNA and proteins

maturation

assembly of phage particles

release

phage lysozyme breaks the cell wall

lysogeny

phage remains latent

retroviruses

single stranded RNA, produce DNA
- viral machinery; get rid of enzyme to cure HIV

reverse transcriptase

to produce DNA from the viral genome
- viral DNA integrates into the host chromosome as a provirus

oncogenes

transform normal cells into cancerous cells; increase rate of cell cycle, makes cells grow at a quicker rate

oncogenic viruses

become integrated into the host cell's DNA and induce tumors

retroviridae

viral RNA is transcribed to DNA (using reverse transcriptase), which can integrate into host DNA

DNA version of RNA that gets inserted into genome

what is a provirus?

reverse transcriptase

How can an RNA virus cause cancer if it doesn't have DNA to insert into a cell's genome?

latent virus

remains in asymptomatic host cell for long periods
- may reactivate due to changes in immunity (cold sores, shingles)

persistent viral infection

occurs gradually over a long period; is generally fatal

viroids

short pieces of naked RNA (loop does not code for anything)
- cause potato spindle tuber disease

prions

proteinaceous infectious particles
- inherited and transmissible by ingestion, transplant, and surgical instruments
- mad cow disease
- sheep scrapie