Microbiology - Outcome 3 Flashcards
what are viruses described as?
small obligate intracellular parasites containing either a DNA or RNA genome
what does ‘obligate intracellular parasite’ refer to?
viruses can only reproduce once they have infected their host organism’s cells
what is a virion?
a complete, mature virus particle and can survive outside the host cells
what is the function of a virion?
to deliver its nucleic acid (DNA or RNA) into the host cell so that the genome can be transcribed and translated by the host cell
what are the 2 basic components of a virion?
nucleic acid and a capsid/protein coat
what is the nucleic acid?
a single or double-stranded DNA or RNA
what does the nucleic acid code for?
- a few structural proteins
- enzymes/regulatory proteins involved in viral replication
what is the capsid?
- protein coat surrounding the nucleic
- coded by the viral genome
- composed of proteins subunits called capsomeres
what are the four shapes of viruses?
- helical symmetry
- icosahedral symmetry
- spherical symmetry
- complex viruses
describe and give examples of helical shape viruses
protein subunits and nucleic acid are arranged in a helix
- rhabdoviruses
- tobacco mosaic virus
describe and give examples of icosahedral shape viruses
regular polyhedron with 20 triangular faces and 20 corners
- adenovirus
describe and give examples of spherical shape viruses
round virus
- influenza
- polio
- varicella-zoster (chickenpox)
describe and give examples of complex viruses
capsid is neither helical or icosahedral
- T4 bacteriophage
- smallpox virus
what is the function of the capsid?
to protect viral genetic material from degradation by enzymes as it is transferred between host cells
what does the viral core consist of?
nucleic acid and capsid
what does a naked virus consist of?
nucleic acid and capsid only
what does an enveloped virus consist of?
nucleic acid, capsid and envelope
describe and give examples of helical symmetry viruses
protein subunits and nucleic acid arranged in helix
- rhabdoviruses
- tobacco mosaic virus
describe and give examples of icosahedral symmetry viruses
regular polyhedron with 20 triangular faces and 20 corners
- adenovirus
- becteriophage X174
describe and give examples of spherical symmetry viruses
round virus particles
- influenza
- polio
- varicella-zoster (chickenpox)
describe and give examples of complex viruses
capsid is neither helical or icosahedral
- T4 bacteriophage
- smallpox virus
what is the function of a capsid?
- to protect viral genetic material from degradation by enzymes as it is transferred between host cells
- aids in virion transfer between host cells
- initiates viral replication
what forms the viral core?
nucleic acid and capsid
what forms the naked virus?
nucleic acid and capsid only
what forms the enveloped virus?
nucleic acid, capsid and envelope
what is the lipid bilayer composed of?
lipids, proteins and glycoproteins
in animal viruses where does the envelope (lipids and carbohydrates) originate from?
the host cell membrane or nuclear membrane depending on whether the virus replicates in the nucleus or cytoplasm of the host cell
what are the envelope proteins coded by?
the viral genome
what is another name for the glycoproteins?
spike proteins/surface antigens
what is the function of the envelope?
- aids penetration of host cell membrane
- confers antigenicity on virus
- enables virus to be attacked by disinfectants or damaged by lipid solvents
what are the key enzymes found in viral particles?
- reverse transcriptase
- integrases
- proteases
- RNA polymerase
- Lysins
describe the role of revere transcriptase
- found in retroviruses (HIV)
- catalyses production of DNA from RNA
- this allows virus to integrate into the host chromosomes to become a log term infection
describe the hole of integrases
- found in retroviruses
- helps integrate viral genetic material into the host chromosome
describe the role of proteases
important in maturation of viral surface proteins to create the infectious virions
describe the role of RNA polymerase
catalyses the copying of RNA genome in RNA viruses such as polio
describe the role of lysins
- hydrolytic enzymes produced by bacteriophages
- cleave host cells wall during final stage of lytic cycle
- allows release of progeny virions from lysed cell
what are the stages of the lytic cycle in bacteriophages?
- attachment
- penetration
- biosynthesis
- maturation
- release
what happens during the attachment stage?
- bacteriophage attaches to host cell
- site on phage binds with complementary receptor
what happens during the penetration stage?
- tail of phage releases enzyme lysozyme to dissolve a portion of the bacterial cell wall
- tail sheath contracts and tail core drives through cell wall
- DNA from phage head passes through the tail core and on through the cell membrane into the bacterial cytoplasm
what happens during the biosynthesis stage?
- phage virus uses bacterium’s nucleotides and enzymes to synthesise multiple copies of viral DNA
- DNA used to encode viral proteins and biosynthesis of viral enzymes and capsid proteins begin using bacterial ribosomes, amino acids and enzymes
what happens during the maturation stage?
fragments of viral DNA and capsids are assembled into complete virions
what happens during the release stage?
- cell membrane lyses and cell wall breaks open due to action of lysozyme encoded for by viral genomes
what are the stages of animal virus replication?
attachment- virus attaches to receptors on host cell membrane
penetration - whole virus is taken in to host cell so need to use enzymes to remove coat (uncaring)
biosynthesis - various options depending on virus DNA/RNA/retrovirus
maturation- no difference
release- envelope is obtained as virus leaves host cell by budding
what are virucidal chemicals?
- chemicals that destroy viruses
- prevents infection
- bleach is an example
what are virustatic agents?
- inhibit host cell entry and/or viral replication
- inhibits by binding to cell receptors or interfering with critical biological process such as DNA replication
- acyclovir is an example
give examples of viruses found in water, what disease they cause and their symptoms
hepatitis A
- hepatitis A
- inflammation of liver
polio virus
- poliomyelitis
- nausea, vomiting, cramps, meningitis, paralysis
norovirus virus
- gastroenteritis
- onset of nausea, vomiting, diarrhoea, headache and low grade fever
how long can cold viruses survive on surfaces?
- several days
- ability to cause infection reduces rapidly - don’t often survive longer than 24hrs
how long can flu viruses survive on surfaces?
24 hours
how long can herpes virus survive on surfaces and skin?
- 4 hrs on surface
- 2 hrs on hands
what are the different types of vaccines?
- live, attenuated
- inactivated/killed
- subunit/conjugate
- mRNA
what are vectors and what are examples of them?
viruses that can be used as a tool to deliver DNA into a cell
- used in gene therapy
- used in covid vaccines
what are viroids?
infectious agents composed of only a single piece of circular ssRNA
what are satellites?
sub viral agents made of RNA and depend on presence of a helper virus for their propagation
what are viroids made of?
circular RNA
what do viroids infect?
plants
do viriods need a helper virus?
no
what disease do viroids cause?
apple scar
what are satellites made of?
linear RNA
what do satellites infect?
plants (and humans - rare)
do satellites need a helper virus?
yes
what disease do satellites cause?
- tobacco necrosis in plants
- hepatitis D in hymans
what are prions made of?
protein
what do prions infect?
plants, animals and bacteria
what diseases do prions cause?
- scrapie
- kuru
- BSE
- CJD
how do viroids replicate?
host cells copy the viroid by mistake
how do satellites replicate?
helper virus provides the enzyme (RNA polymerase) needed for replication
how do prions replicate?
conformational changes occur in existing cellular prion proteins (PrPc)
