micro test 2

acellular agents

• viruses

• viroids

• satellites

• prions

viruses

protein and nucleic acid

viroids

only RNA

satellietes

only nucleic acids

prions

proteins only

viruses may be defined as:

• acellular organisms whose genomes consist of nucleic acid

• obligately replicate inside host cells using host metabolic machinery and ribosomes.

viral properties:

• inert filterable agents

• obligate intracellular parasites

• cannot make energy or proteins independent of host cell

• genome is RNA or DNA but no both

• naked capsid or envelope with attached proteins

• do not have the genetic capability to mulitiply by division

• non living entities

viruses named based on disease

• poxvirus

• hepatitis virus

• HIV

• measles virus

viruses named based on cytopathology

• respiratory syncytial virus

• cytomeglovirus

viruses named based on site of isolation

• adenovirus

• enterovirus

• rhinovirus

viruses named based in places discovered or people that discovered them

• Epstein-Barr virus

• rift valley fever

virus named based on biochemical features

• retrovirus

• picornavirus

• hepadnavirus

Hepatitis virus

liver inflammation

pox virus

pock like lesion in skin

measles virus

pediatric skin rash

HIV

human immunodiffency virus

respiratory syncytial virus

many cells join to look like one cell

rhinovirus

similar to influenza

retrovirus

reverse transcriptase enzyme

picornavirus

small rna - RNA virus

hepadnavirus

liver and dna virus

virus classification is based on

• morphology

• serology

• genetic material

  • form of nucleic acid

  • genetic organization

  • sequence homology

morphology is determined by

electron microscopy

serology is determined by

antigenic cross reactivity

DNA virus can be

single stranded (- or +) or double strand

RNA virus can be

single stranded (- or +) or double stranded

(+)ss RNA

mRNA can transcribe

(-)ss RNA

has to convert to mRNA to be transcribed

virion

complete mature infectious virus particle

provirus

a virus genome that has integrated itself into the DNA of a host cell

viroids

are very small (200-400 nucleotides )circular RNA molecules with a rod-like secondary structure. They have no capsid or envelope and are associated with certain plant diseases.

virusoids

are satellite, viroid like molecules, somewhat larger than viroids (~1000 nucleotides), which are dependent on the presence of virus replication for multiplication. packaged int ovirus capides as passengers.

example of virusoids

hepatitis (delta) virus

prions

infectious agents generally believed to consist of a single type of protein molecule with no nucleic acid component

VLP

virus like particle

papiloma virus

cervical canver (example o

VLP makeup

• capsid only

• no nucleic acid

• no envelope

• sphere filament

example of VLP

hepatitis B (HBV) hepadona virus

Group I

ds DNA virus

Group II

ss DNA virus

Group III

ds RNA virus

Group IV

+ ss RNA virus

Group V

- ss RNA virus

Group VI

ss RT RNA virus

Group VII

ds RT DNA virus

ex Group I

• pox virus

• herpes virus

• adenovirus

ex Group II

Parvo virus

ex Group III

picorna virus

ex Group IV

reo virus

ex Group V

rhabdovirus

ex Group VI

HIV

ex Group VII

HBV

RT

reverse transcriptase

reverse transcriptase

RNA—> DNA

against central dogma

naked virus/ non envelopedvirus

Nucleic acid + capsid

enveloped virus

nucleic acid + capsid +envelope (optional)

prions lead to

neurological degenerative diseases

kuru

piron in new guinae cannibalism

scrapie

prion in sheep

prions caused this outbreak

mad cow disease

suffix of family of virus

-viridae

suffix of subfamily of virus

-virinae

suffix of genus of virus

-virus

viruses are classified according to 5 main characteristics

• host organisms

• nature of nucleic acid in the virus particle (virion)

• symmetry (structure) of protein shell (capsid)

• presence of absence of envelope. (lipid membrane)

• dimension of virus/ capsid

icosahedral

• capsid: protein coat

• capsomeres subunits of the protein coat

• symmetry

  • 12 corner

  • 20 faces

  • 30 edges

capsomers

• ring or knob-shaped units made of 5 or 6 protomers

• pentamers (pentons)

• hexamers (hexons)

prophage

can be integrated into bacteria chromosome

episome

integrated plasmid in chromosome

pentamers

5 subunit capsomers

hexamers

6 subunit capsomers

isosahedral capsid attaches to

envelope

outer flexible membranous layer

examples of rna virus (mutate frequently)

• flu virus

• covid19

• hiv

rna virus

rna dependent rna polymerase

rt virus

rna dependent dna polymerase

quasi species

one cell containing multiple variants of the virus

influenza virus

neurominidase enzyme

destroys neuroaminic acid in the plasma membrane

methods of replication

lytic cycle and lysogenic cycle

lytic cycle

the virus enters the cell, replicates itself hundreds of times, and then burst out of the cell, destroying it.

lysogenic cycle

the virus DNA integrates with the host DNA and the host’s cell helps create more virus DNA. an environmental change may cause the virus to enter the lytic cycle

envelope protein in HIV attachment

gp 120

envelope protein in Hiv fusion

gp 41

antigenic drift

point mutation

point mutation

one nucleotide change

antigenic shift

reassortment

reassortment

segments interchange

example of antigentic drift

covid19

example of antigenic shift

influenza and swine

example of jumping virus

SIV —> HIV

step one of virus replication

attachment (absorption )

step two of virus replication

penetration (injection)

step 3 of virus replication

synthesis of nucleic acid and protein

step 4 of virus replication

assembly and packaging

step 5 of virus replication

release (lysis)

pox virus variations

• vaccina virus

• variola virus

• monkey pox

vaccina virus

non infectious pox virus

variola virus

causes small pox

used to make vaccine

vaccina virus

largest virus (0.2 micrometers)

pox virus

smallest virus

parvo virus