topic 8: viruses Flashcards
what are viruses defined as and why?
- defined as non-cellular infectious particles
- because they do NOT consist of cells (do not fit the definition of a living organism)
what is the approximate size of viruses?
10 - 300 nm diameter
define viruses
obligate intracellular parasites:
- depend on the host cells for their replication
- use enzymes of the host cells in order to replicate
what are the characteristics of viruses?
- obligate intercellular parasites
- can infect both eukaryotes and prokaryotes
- bacteriophages
- important pathogenic agents in both animals and plants
what are bacteriophages (phages)?
viruses that infect only prokaryotes (bacteria)
compare the sizes of eukaryotes, prokaryotes, and viruses
virus - 0.05μm
phage - 0.1μm
bacterium - 1-10μm
eukaryotic cell - 10-100μm
** bacteria is around 10-100x smaller than eukaryotic cells
** viruses are much smaller than both prokaryotic & eukaryotic cells
what is the essential structure of a virus? what is an additional structure that some viruses have?
essentially made from:
(1) nucleic acid (DNA or RNA)
(2) a protein capsid
additional structure:
(3) envelope (an external protective layer)
what is a capsid? what is it responsible for?
- a protein coat
- encapsulates the nucleic acid and protects the viral genome from nucleases
- may have fibers that assist the attachment of the virus to the host cell
what is the function of an envelope? what does it consist of?
- consists of membrane
- carries glycoproteins
- is required during the exit of viruses from cells that they infect
- only present in enveloped viruses
viral genomes may consist of?
- single or double-stranded DNA
- single or double-stranded RNA
what are the 2 types of viruses that can exist based on the type of nucleic acid they contain?
- DNA viruses
- RNA viruses
capsids are built from protein subunits called?
capsomeres
what are the types of shapes or symmetry that a capsid can have?
- icosahedral (spherical) symmetry
- helical symmetry
regarding viral capsid structures, what type of capsid structure do each of the following have:
(1) tobacco mosaic virus (TMV)
(2) adenoviruses
(3) influenza viruses
(4) bacteriophage T4
(1) non-enveloped, helical capsid
(2) non-enveloped, icosahedral capsid
(3) enveloped, helical capsid
(4) non-enveloped, icosahedral capsid
what type of nucleic acid do each of the following have:
(1) tobacco mosaic virus (TMV)
(2) adenoviruses
(3) influenza viruses
(4) bacteriophage T4
(1) RNA virus
(2) DNA virus
(3) RNA virus
(4) DNA virus
most animal viruses are _____, unlike most plant viruses which are _____
- enveloped
- non-enveloped
ALL phages are _____
non-enveloped
what does the viral envelope contain?
viral glycoproteins which bind to specific receptor molecules on the surface of the host cell
what function does the viral envelope help with?
- it helps the virus infect their host cells
- envelope fusion with host cell membrane
what is the origin of viral envelopes?
they are derived from the host cell’s membranes (mainly the plasma membrane but can be the nuclear membrane)
how does specificity of a bacteriophage work?
different types of phages infect specific different bacteria types
when is the viral envelope formed?
- during the exit of the viral particles from the host cells
- therefore, they contain a combination of viral and host cell molecules
describe the structure of a phage
- capsid head
- protein tail
what is the function of the phage capsid head?
encloses their nucleic acid (commonly DNA)