viruses

characteristics of viruses

non-living—don’t grow, respire, or move; reproduce only with help from host cell (cell it infects), named for disease they cause or place they infect, or are given a number, possibly evolved from host cells or plasmids

plasmids

a small, circular, double-stranded DNA molecule that is distinct from a cell's chromosomal DNA

1 micron

1/1000 of a milimeter

1 nanometer

1/1000 of a micron (aprox. size of a virus)

nucleic acid core

RNA or DNA (codes only for virus production)

capsid

a protein coat surrounding the nucleic acid core

viral envelope

made of proteins, phospholipids, and glycoproteins (projections that help recognize host cell and bind to it)

structure of a virus

1. nucleic acid core

2. surrounded by capsid

3. some have viral envelope

shapes of viruses

1. helical

2. polyhedral

3. bacteriophage

bacteriophage

virus that infects bacteria

injection

attach to cell membrane and inject nucleic acid (bacteriophages do this)

fusion

some enter cell by attaching to membrane receptors and fusing its membrane with host cell membrane (capsid and nucleic acid enter)

endocytosis

enter in a vessicle

in plants (entry)

weak areas in cell walls allow viruses to enter; then it produces protein to enter other cells

viral production cycles

1. lytic

2. lysogenic

lytic cycle

1. attachment

2. injection of DNA and breaking down host DNA

3. replication

4. assembly

5. release viruses by lysing and killing host

virulent phase

period during which the virus is active and causing damage

lysogenic cycle

1. attachment

2. injection of DNA

3. joining viral DNA with host DNA forming prophage (or provirus in non-bacteriophage viruses)

4. cell reproduces making copies of prophage/provirus too

temperate phase

a phase in the life cycle of certain viruses where they remain dormant and do not actively cause damage

prophage/provirus can _____

remain inactive for years and enter lytic cycle producing viruses and killing the host

retrovirus

RNA is the nucleic acid, virus also injects reverse transcriptase which copies viral RNA into DNA becoming a provirus, ex: HIV

provirus

a form of viral genetic material that has been integrated into the genome of a host cell

RNA lytic viruses

have RNA, but no reverse transcriptase, so can’t make a DNA copy, do have enzymes to copy RNA and follow the lytic cycle

treatment

no cure (treat symptoms only), prevention (vaccines, disinfect and sterilize when appropriate), antiviral drugs which interfere with reproduction (fake DNA nucleotides or prevent protein production)

viroids

infect plants, RNA molecules without capsids, make more viroids once in cell, stunt growth of plant

prions (protein infectious particles)

infect animals, contain only protein, form protein clumps which change other proteins into prions