Mim - Lecture 24

Front 1

24.1

viruses

Back 1

- obligate intracellular parasites
- genome contains either RNA or DNA as the genetic information.
- protective protein shell (capsid) surrounds the nucleic acid genome and frequently the capsid is enclosed within an envelope (contains both protein and lipid)

Front 2

24.2

viral assembly

Back 2

- occurs by the process of self-assembly by which the component parts aggregate into the proper configuration

Front 3

24.3

bacteria vs. viruses

size and visability

Back 3

size:
bacteria: > 500 nm
viruses: < 300 nm

visability:
bacteria: light microscope
viruses: electron microscope

Front 4

24.4

bacteria vs. viruses

filterability and cultivation

Back 4

filterability:
bacteria: non-filterable (remian on top of the filter)
virsus: filterable (pass through)

cultivation:
bacteria: artificial media
viruses: living host cells

Front 5

24.5

bacteria vs. viruses

replication and nucleic acids

Back 5

replication:
bacteria: binary fission
viruses: complex

nucleic acids:
bacteria: DNA + RNA
viruses: DNA or RNA

Front 6

24.6

viral morphology

Back 6

- 20-25 nm (parvoviruses and picornaviruses)
- 200-300 nm (poxviruses)
- symmetry of protein coat or capsid surrounding the nucleic acid can be either helical or cubical (icosahedral) both together are referred to as nucleocapsid
- capsid is composed of subunits or capsomers
- capsomers: used to build more complex icosahedral capsids
- single polypeptide chains are used to build the helical capsids

Front 7

24.7

icosahedral symmetry

Back 7

- cubic symmetry found in viruses is based on the icosahedron which has 20 faces, each an equilateral triangle, 12 vertices and 30 edges

Front 8

24.8

helical symmetry

Back 8

- capsomers and nucleic acid genomes of several RNA viruses undergo self-assembly as a cylindrical nucleocapsid in which the capsomeres are arranged like a spiral staircase or helix

Front 9

24.9

complex

Back 9

- virus doesn't fall into either of the groups above (poxvirus)

Front 10

24.10

naked icosahedral

Back 10

- these viruses consist of icosahedral nucleocapsid (parvoviruses, picornaviruses, adenoviruses)

Front 11

24.11

envloped icosahedral

Back 11

- the virion of this group consists of an icosahedral nucleocapsid surrounded by an envelop (herpesviruses, togaviruses)

Front 12

24.12

naked helical

Back 12

- these viruses appear to be long rods; however they consist of an RNA genome interwined with protein structural units to form a helix. Although none of the animal viruses are in this group, many of th eplant viruses are (tobacco mosaic virus)

Front 13

24.13

enveloped helical

Back 13

- viruses in this group consist of a flexible helical nucleocapsid surrounded by an envelope.
- orthomyxoviruses and paramyxociruses

Front 14

24.14

complex ciruses

Back 14

- some viruses do not fit into any of the above categories. The poxviruses are the most complex of the animal viruses

Front 15

24.15

viral nucleic acid

Back 15

- either DNA or RNA, generally not both
- all viral genomes are haploid and contain one copy of each gene, except retroviruses which are diploid

Front 16

24.16

DNA viruses: nucleic acid

Back 16

- may be single or double stranded including both linear and covalently closed circular DNA
- largest DNA viruses - poxviruses and herpesviruses - 100-200x10^6 daltons.
- 2 strands of poxvirus DNA are covalently cross-linked at their termini, so that on denaturation the molecule becomes a large single-stranded circle

Front 17

24.17

RNA viruses: nucleic acid

Back 17

- genome may be single or double stranded either segmented or nonsegmented.
- arenavirus genomes have 2 segments, bunyavirus genomes have 3 segments, orthomyxovirus has 7 or 8, and reovirus has 10, 11 or 12 segments

Front 18

24.18

RNA viruses are classified according to:

Back 18

whether the RNA is of the same polarity as mRNA (+ strand_ or whether RNA is of th eopposite polarity to mRNA (- strand)

Front 19

24.19

picorna and togaviruses

Back 19

some RNA viruses like Picorna and Togaviruses contain RNA which exists as a non-segmented RNA. At the 3' end is a polyadenylic acid chain similar to eurkaryotic mRNA

Front 20

24.20

the flu

Back 20

- influenza A virus contains 8 segments of RNA
- surrounding the gentic material is a capsid containing the following peplomers (glycoproteins)
- hemagglutinin (HA) assists the virus awith attaching to the host ell
- neuraminidase is responsible for the release and spread of the virus

Front 21

24.21

antigenic drift

Back 21

- occurrence of point mutations whithin HA and neuraminidase.

Front 22

24.22

antigenic shift

Back 22

- 2 different strains of a virus, combine to form a new virus, having a mixture of the different surface antigens of the 2 original strains

Front 23

24.23

terminal redundancy

Back 23

- nucleic acid of several viruses are terminally redundant or repetitious. Their base composition may be respresented as ABC...XYZA
- herpesvirus DNA: length of the repeated sequence is about 400 nucleotide base pairs. Terminal redundancy of this type is also exhibited by the RNA or RNA tumor viruses
- other virus genomes like adenovirus, parvovirus, and poxvirus DNAs are also terminally redundant but here the reported sequences are inverted or reversed

Front 24

24.24

segmentation

Back 24

- genomes of various RNA viruses including reoviruses (10 segments), rotaviruses (11 segments), influenza viruses (8 segments) have been shown to be segmented
- genome of RNA tumor viruses: 2 identical single-stranded RNA molecules -> diploid genome

Front 25

24.25

genetic relatedness of viral nucleic acids

Back 25

- determination of similarity is measured by how extensively their nucleic acids can hybridize. this is done by denaturing dsDNA to single-stranded state and allowing the strands to reanneal. If the genomes are related, pairing will occur, if not then no pairing (hybridization) will occur.

Front 26

24.26

infectivity of animal virus nucleic acids

Back 26

- viral nucleic acid contains all the info for the virus particle. The nucleic acid of picornaviruses, togaviruses, coronaviruses, papovaviruses, adenoviruses and herpesviruses are infectious.

Front 27

24.27

glycoproteins

Back 27

- viral envelopes contain glycoproteins (hemagglutinins) in the form of spikes or projections.

Front 28

24.28

hemagglutination

Back 28

- both enveloped or naked biruses can agglutinate RBCs of certain animal species. RBCs contain receptors on their surface for hemagglutinins on the virus particle.
- hemagglutination titer can be used to quantitate total virus numbers

Front 29

24.29

viral envelopes contain:

Back 29

- complex mixtures of neutral lipids, phospholipids and glycolipids.
- composition usually reflects that of the membranes of the host cell from which envelope virus bud.
\- therefore viruses grown in different tissue culture cells may contain envelops with widely different lipid compositions.

Front 30

24.30

vesicular stomatitis virus

Back 30

- single stranded RNA virus and looks bullet shaped, just like rabies. both of these viruses are easy to lyse with detergents

Front 31

24.31

adenovirus

Back 31

- has no envelope and has a capsid with a hexon/penton structure
- uses its tail fibers to attach to epithelial cells

Front 32

24.32

papillomavirus

Back 32

- looks similar to adenovirus

Front 33

24.33

vaccinia virus

Back 33

- a pox virus with complex morphology