viruses lecture + ebola lab

structure of all viruses

nucleic acid core surrounded by a capsid (protein) and no cytoplasm

what do only SOME of viruses have?

specialized enzymes within the core and an envelope from the host cell membrane

nucleic acids can be

DNA or RNA

circular or linear

single or double-stranded

host range

type of organisms infected by the virus, which has a limited range

tissue tropism

a virus inside a host infecting only certain tissues (ex. rabies only infects neurons, brain cells)

host cells are?

REQUIRED for viral replication

what happens to the host cells after infection?

they are destroyed

viruses lack ___ for protein and nucleic acid synthesis

ribosomes and enzymes.

what do viruses use to replicate?

the host cell’s ribosomes and enzymes/ transcription and translation machinery

early genes

take over host cell’s machinery

intermediate and late genes

release virally from the infected cell

helical (viral shape)

rod or threadlike

icosahedral (viral shape)

nearly spherical but not quite.

why is morphology highly diverse?

viruses can be naked, complex, or enveloped

what does shape NOT determine what the virus does?

what the virus infects

RNA viruses

most common, 70% of viruses contain these. Mostly single-stranded with high mutation rates. will RARELY be linear

DNA viruses

double-stranded and replicated in the nucleus

retroviruses

single-stranded RNA is reverse transcribed to DNA, uses reverse transcriptase.

Viral classification is based on:

taxonomy, disease caused by it, type of host infected, genome expression

virus taxonomy

order, family, subfamily, and genus. Has 15 ranks, 8 primary and 7 secondary.

Disease they cause

not always useful, some viruses do not cause disease. Some viruses cause different diseases in different organisms.

host infected

viruses can infect multiple hosts

genome expression

Baltimore classification sorts by genome structure (from DNA or RNA to mRNA) and expression

Bacteriophage (or just “phage”)

viruses that ONLY infect bacteria. very diverse

2 phage cycles

Lytic and Lysogenic

Lytic cycle

cell rupture. Short and destructive. 5 steps.

Lytic cycle steps

1. attachment or adsorption

2. penetration or injection

3. synthesis

4. assembly

5. release

attachment/adsorption

targets bacterial outer surface, limits the hosts range when binding to surface

penetration/injection

pierces cell wall to infect viral genome (w/ syringe-like structure)

synthesis

phage uses cell machinery to replicate viral components

assembly

assembly of viral components (particles, genetic material and capsid proteins)

release

mature virus particles are released through the cell wall.

lysogenic cycle

when a temperate phage infects a host cell and a genome is integrated into the genome of the host cell.

lysogenic cycle

infection → replication → waiting period

latent phase

host cell not immediately dying. the virus nucleic acid is integrated into the host genome

prophage

the temperate/lysogenic phage when integrated

phage conversion

some viral genes are expressed, altering the host cell’s phenotype

the lysogenic cycle converts…

harmless cells into disease-causing ones

viral infections are based on…

how rapid and frequently the virus is produced and appearance of associated symptoms.

persistent infections

laten or chronic, will stick with the host for prolonged periods of time

acute infections

rapid replication of the virus and onset of symptoms. can cause major world events (outbreak, epidemic, pandemic)

Influenza (flu)

one of the most lethal viruses, pandemics of 1918-1919 infected 1/3rd of the worlds population. the flu is enveloped and infects animals.

Hemagglutinin (H) / flu subtype

aids in viral ENTRY

Neuraminidase (N) / flu subtype

aids in viral EXIT

Antigenic DRIFT

H (hemagglutinin) and N (neuraminidase) molecules accumulate RANDOM mutations, making the previous vaccine-induced immunity no longer protective.

Antigenic SHIFT

genetic recombination can occur when two viruses enter the same cell (major combinations, only in influenza A)

Zoonotic viruses

viruses that infect a variety of animals, spill over from nature

persistent viral infections

can be chronic, latent, or slow. the virus will be detectable in the host for years after infection or for life.

Cancer

cancer causing viruses are rare but deadly. caused by viruses altering the growth of healthy cells. Blocks cell death and promotes cell division.

Prions (NOT viruses, simpler)

misfolded proteins

viroids (NOT viruses OR proteins)

tiny, unenveloped molecules of circular RNA. made up of 250-400 nucleotides. Causes disease in economically important crops. Small interfering RNAs (siRNAs) may be produces during infection, effects growth and development.

ebola is..

zoonotic

ebola symptoms

uncontrollable internal bleedings, high fever (hemorrhagic). Liver and kidney failure, vomiting and diarrhea.