III Virus Structures, Components, and Function

This is a single folded polypeptide chain.

subunit

This is the unit from which capsids or nucleocapsids are built; one or more subunits.

structural unit

What forms the structural unit of viruses?

capsids or nucleocapsids

protomer of viruses that are asymmetric in nature

structural unit

Where does the word capsid come from?

capsa = Latin, box

This is a protein shell surrounding genome.

capsid

This is the nucleic acid-protein assembly within particle and used when it is a discrete substructure.

nucleocapsid

this is the core of the virus structure

nucleocapsid

This is a host cell-derived lipid bilayer.

envelope

another term for the viral membrane

envelope

This is the infectious virus particle.

virion

This is a complete virus particle that represents the extracellular phase of the virus life cycle.

virion

What are the functions of the virion?

protects genome, delivers genome, delivers protein contained in the virion, interactions with the host

This is constructed from many copies of 1 or few types of protein subunits (protomers).

capsid or protein coat

conversion units of nanometers

10-9 meters = 10 Å = 0.001 microns

what is the range if virion size

10 to 300 or 400 nm in diameter

size of alpha helix, DNA and ribosomes in diameter

1nm, 2nm, 20 nm

size of poliovirus and pandoravirus

30nm, 1000 nm

what virus was described in 2003 and sequenced in 2004

Mimivirus

in 2011, this was the largest virus having a size of 440 nm and having the most complex genome of 1.2 mB

Megavirus chilensis

in 2013, these viruses were discovered and they infect amoebae and are larger than some bacterua, having a size of 1.0 um and a genome size of 1.5 um, larger than of the megavirus chilensis

pandoraviruses

these viruses has a size of 1.5 um and genome size of 0.6 Mb

Pithovirus sibericum

which virus cannot be filtered and can be seen under the lgiht microscope

Pithovirus sibericum

a complete virus particle that represents the extracellular phase of the virus life cycle

virion

What are the functions of the capsid ?

protects the viral genome using the capsid

recognition of & interaction with host cell

facilitate transfer of viral NA and proteins

determines the antigenic characteristic of the virus

function of the virion

the functions of the virion are:

→ protects genome using capsid

→ delivers genome to host cell compatible with the virus

→ delivers protein contained in the virion

→ interactions with the host

This is the basic protein building block of the capsid.

protomer

This is a morphological unit on the surface of the virus.

capsomere

what are the possible conformation of protomers in the capsomere

pentamer protomers at the vertices

hexamers protomers on the faces

What are the types of virion symmetry?

icosahedral, helical, complex, rod and cone

What are the most common types of virion symmetry?

helical and icosahedral

common symmetry in plant viruses

helix, tobacco mosaic virus

most common symmetry in general, example

icosahedral, adenoviruses

this symmetry may induce rigidity or flexibility, example

rod

Describe the faces an icosahedral virus has

20 faces with equilateral trianles

What type of triangle are the faces of an icosahedron?

equilateral

How many vertices does an icosahedron have?

12 vertices

How many edges does an icosahedron have??

30 edges at each of which the sides of the triangles meet

This symmetry is exemplified by many common plant and animal viruses.

icosahedral (cubic)

describe the monomer of icosahedral symmetry

60 identical protein molecules (minimum of 3 per

triangular face)

In icosahedral virion symmetry, what capsomere composes the vertices?

pentamers

In icosahedral virion symmetry, what capsomere composes the faces?

hexamers

what are the two protein species of the capsid that makes up the cowpea mosaic virus

12 pentamers

20 hexamers

what are the three axes of symmetry of an icosahedron

vertex ( 5 - fold )

trangular face ( 3- fold )

edge ( 2 - fold )

What are the functions of icosahedral symmetry?

allows tight packing of subunits,

size of subunits can be smaller (economizing on genetic info),

most efficient arrangement for subunits in a closed shell (uses the smallest # of units to build a shell)

why is it that the icosahedron is the most efficient arrangement for viruses

it uses the smallest number of units to build a shell

In this virion symmetry, protein subunits arranged helically like hollow cylinders around the coil and are coated

helical

how is the nucleic acid packaged for helical symmetry inside its coat proteins

nucleic acid is coiled in the form of an alpha helix

how does the helical shape influences the properties of plant viruses and animal viruses

plant viruses - rigid

animal viruses - long and flexible

what symmetry does measels virus exhibit and describe

helical

the complete nucleocapsid is folded and enclosed within an envelope, with a ssRNA

True or false: the size of helical capsid is influenced by both NA and capsomeres

True

what are the two factors that infleunces the size of helical symmetry of viruses

NA and capsomeres

the diameter or width is determined by

size and shape protein interaction

In helical virion symmetry, its length is determined by

length of nucleic acid

This virion symmetry is common in atypical viruses such as poxvirus & bacteriophage T4.

complex

What viruses have a complex virion symmetry?

poxviridae( oval/brick shaped )

bacteriophages

orthopoxvirus ( surface tubules )

parapoxvirus ( surface filaments )

HIV -1 ( conical shape )

Baculovirus ( rod shaped )

what is the symmetry exhibited by Baculovirus ?

complex symmetry, rod shape

what is the symmetry exhibited by HIV -1 viruses?

complex symmetry, conical shape

what is the symmetry exhibited by parapoxvirus viruses?

complex symmetry, surface filaments

what is the symmetry exhibited by orthopoxvirus viruses?

complex symmetry, surface tubules

what is the symmetry exhibited by poxviridae viruses?

complex symmetry, oval/brick shaped

describe the envelope that surrounds HIV and Baculovirus

viral genoe is coated in a highly basic protein ( enveloped virions )

What is the difference between Orthopoxvirus and Parapoxvirus in terms of surface composition?

Orthopoxvirus has surface tubules while Parapoxvirus has surface filaments

This stores the genetic info of the virus.

viral genome

principle for viral genomes in relation to its host

the genome must be compatible with the host cell machinery. Compatible in a way that it can be recognized and decoded by the particular type of cell it parasitized

What are the four categories of viral genomes in terms of strandedness?

dsDNA, ssDNA, dsRNA, ssRNA

What are the nucleic acid configurations of the viral genome?

linear, circular, segmented

different types of single stranded viral genomes

positive (+) sense, negative (-) sense, or ambisense

Which between positive- and negative-sense ssRNA has the same sense as RNA and can function directly as mRNA?

positive sense strand 4

What is the definition of an ambisense ssRNA?

the polarity of the genome is part positive and part negative

Most plant viruses have what type of genomes

ssRNA

Most fungal viruses have what type of genomes

dsRNA

Most prokaryotic viruses have what type of genomes

dsDNA

The large virus genomes are composed of what type of genomes

dsDNA

The largest RNA genomes belong to what kind of viruses

coronaviruses (33 kb ssRNA)

The largest virus genome belongs to what virus and what size

Pandoravirus, with 2.8 Mb size

what kind of genome do Paroviruses have?

ssDNA, linear

what kind of genome do poxviruses have

dsDNA linear

what kind of genome do PJAGE gama X174 have

ssDNA , circular

what kind of genome do baculoviruses have

ds DNA circular

what kind of genome do tobacco mosaic viruses have

ssRNA linear

what kind of genome do reoviruses have

ds rna, linear

what kind of genome do hepatitis delta viruses have

ss RNA circular

True or false: segmented genomes are much more common amongst RNA viruses than DNA viruses

True

This NA configuration is more common amongst plant viruses

multipartite genomes

Segmented genomes are much more common amongst viruses.

RNA viruses than DNA viruses

What are the types of NA configurations for segmented genomes in viruses?

monopartite and multipartite

In this type of NA configuration for segmented genome, all the segments are present in a single virion.

monopartite

In this type of NA configuration for segmented genome, the genome is divided into separate parts enclosed in the same capsid

monopartite

How many RNA segments does influenza virus (orthomyxoviridae) have?

8 RNA segments, with each segment coding for one protein

what specific segment of the influenza viruses in its segmented genome codes for hemagglutinin

segment 4

In this type of NA configuration for segmented genome, the segments are not contained in the same capsid.

multipartite

In this type of NA configuration for segmented genome, each genome segment is packaged into separate virus particles

multipartite

Why are multipartite segmented genomes possible in plant viruses?

because they are delivered by insects

What is the advantage of multipartite segmented genomes?

solves the problem of breakages

What is the disadvantage of multipartite segmented genomes?

all virus particles must be taken up by a single host cell to establish productive infection

What are the types of viral proteins?

structural proteins and non-structural proteins

These are proteins that are components of the virions.

structural proteins

What are the functions of structural proteins?

protection of the virus genome,

attachment of the virion to the host cell (for many viruses),

fusion of the virion envelope to a cell membrane,

provide structural symmetry,

determine antigenic characteristics of the virus

These are proteins synthesized by the virus in an infected cell but they are not virion components.

non-structural proteins