Morphology

Morphology (biology)

In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....

Virions consist of a capsid

Capsid

A capsid is the protein shell of a virus. It consists of several oligomeric structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may not correspond to individual proteins, are called capsomeres. The capsid encloses the genetic...

. Virus capsid is not enveloped, round with icosahedral symmetry

Icosahedral symmetry

A regular icosahedron has 60 rotational symmetries, and a symmetry order of 120 including transformations that combine a reflection and a rotation...

. The isometric capsid has a diameter of 35-39 nm. Capsids appear round to hexagonal in outline. The capsid surface structure reveals a regular pattern with distinctive features. The capsomer arrangement is clearly visible. Capsid with 32 cup-shaped depressions.

Physical chemistry

Physical chemistry

Physical chemistry is the study of macroscopic, atomic, subatomic, and particulate phenomena in chemical systems in terms of physical laws and concepts...

 and Physical property

Physical property

A physical property is any property that is measurable whose value describes a physical system's state. The changes in the physical properties of a system can be used to describe its transformations ....

The molecular mass

Molecular mass

The molecular mass of a substance is the mass of one molecule of that substance, in unified atomic mass unit u...

 (Mr) of virions is 15 x 10⁶. Virions have a buoyant density in Caesium chloride

Caesium chloride

Caesium chloride is the inorganic compound with the formula CsCl. This colorless solid is an important source of caesium ions in a variety of applications. Its crystal structure forms a major structural type where each caesium ion is coordinated by 8 chlorine ions...

 (CsCl) of 1.33-1.36 g/cm³. The density gradient of virions in Potassium Tartrate-Glycerol is 1.29 g/cm³. The sedimentation coefficient

Sedimentation coefficient

The sedimentation coefficient s of a particle is used to characterize its behaviour in sedimentation processes, notably centrifugation. It is defined as the ratio of a particle's sedimentation velocity to the acceleration that is applied to it .The sedimentation speed v_t is also known as the...

 is 170-187 svedberg

Svedberg

A svedberg is a non-SI physical unit used for sedimentation coefficients.  It characterizes the behaviour of a particle type in sedimentation processes, notably centrifugation.  The svedberg is technically a measure of time, and is defined as exactly 10-13 seconds A svedberg (symbol S, sometimes...

 (s_20,w); of the other(s) are peak 160-170 svedberg

Svedberg

A svedberg is a non-SI physical unit used for sedimentation coefficients.  It characterizes the behaviour of a particle type in sedimentation processes, notably centrifugation.  The svedberg is technically a measure of time, and is defined as exactly 10-13 seconds A svedberg (symbol S, sometimes...

 (s_20,w) (believed to consist of defective interfering particles). Under in vitro

In vitro

In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

 conditions virions are inactivated in acid environment of pH

PH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...

 4.5-7; stable in alkaline environment of pH 7-10.5. Virions are not stable at raised temperature in presence of high concentration of Mg

Mg

MG, M.G., M-G and variants may refer to:Business* MG Cars , a British automobile manufacturer, now part of SAIC* Champion Air , an American charter airline with IATA code MGEducation...

++. Virions are sensitive to treatment with trypsin

Trypsin

Trypsin is a serine protease found in the digestive system of many vertebrates, where it hydrolyses proteins. Trypsin is produced in the pancreas as the inactive proenzyme trypsinogen. Trypsin cleaves peptide chains mainly at the carboxyl side of the amino acids lysine or arginine, except when...

 (in some strains, not sensitive to treatment with mild detergents, or ether

Ether

Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...

, or chloroform

Chloroform

Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...

. The infectivity

Infectivity

In epidemiology, infectivity refers to the ability of a pathogen to establish an infection. More specifically, infectivity is a pathogen's capacity for horizontal transmission that is, how frequently it spreads among hosts that are not in a parent-child relationship...

 is enhanced after treatment with trypsin (in some strains).

Nucleic acid

Nucleic acid

Nucleic acids are biological molecules essential for life, and include DNA and RNA . Together with proteins, nucleic acids make up the most important macromolecules; each is found in abundance in all living things, where they function in encoding, transmitting and expressing genetic information...

The genome

Genome

In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 is not segmented and contains a single molecule of linear positive-sense, ssRNA

RNA virus

An RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...

. Minor species of non-genomic nucleic acid are some times also found in virions. The encapsidated nucleic acid is mainly of genomic origin, but virions may also contain subgenomic RNA. The complete genome is 7450 nucleotides long. The genome has a guanine

Guanine

Guanine is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine . In DNA, guanine is paired with cytosine. With the formula C5H5N5O, guanine is a derivative of purine, consisting of a fused pyrimidine-imidazole ring system with...

 + cytosine

Cytosine

Cytosine is one of the four main bases found in DNA and RNA, along with adenine, guanine, and thymine . It is a pyrimidine derivative, with a heterocyclic aromatic ring and two substituents attached . The nucleoside of cytosine is cytidine...

 content of 49.3-50.1 %. The 5' end of the genome has a usually genome-linked protein (VPg

VPg

VPg is a protein attached to the 5' end of RNA during RNA synthesis in a wide variety of viruses including Picornaviridae such as Foot-and-mouth disease and poliovirus . VPg stands for "viral protein genome-linked".-Attachment during RNA synthesis:...

), or methylated nucleotide cap (in the case of Hepatitis E virus

Hepatitis E virus

Hepatitis E virus is the infective organism that causes hepatitis E.The viral particles are 27 to 34 nanometers in diameter, are non-enveloped and contain a single-strand of positive-sense RNA that is approximately 7300 bases in length. The virus particle was first visualised in 1983 but was only...

). The 3' terminus has a poly (A)

Poly(A)-binding protein

Poly-binding protein is a RNA-binding protein which binds to the poly tail of mRNA. The poly tail is located on the 3' end of mRNA...

 tract. Each virion contains a full length copy, or defective interfering copies

Defective interfering particle

Defective interfering particles are virus particles that are missing part or all of their genome. Because of these deletions in their genome, DIPs cannot sustain an infection by themselves. Instead, they depend on co-infection with a suitable helper virus. The helper virus provides the gene...

.

Proteins

The viral

Virus

A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...

 genome encodes viral structural protein

Viral structural protein

A viral structural protein is a viral protein that is a structural component of the mature virus.Examples include the SARS coronavirus 3a and 7a accessory proteins....

. Virions consist of 1 structural protein(s) (major species located in the capsid.

Viral structural protein: Capsid protein has a molar mass

Molar mass

Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...

 of 59000-71000 Da; is the coat protein

COPI

COPI is a protein complex that coats vesicles transporting proteins from the cis end of the Golgi complex back to the rough endoplasmic reticulum , where they were originally synthesized and between golgi compartments. This type of transport is termed as retrograde transport...

. Capsid protein has a molecular mass of minor 'soluble' 28-30 kDa.

Genomic organization

Genomic organization

right|thumb|300px|Genome sizes and corresponding composition of six major model organisms as pie charts. The increase in [[genome]] size correlates with the vast expansion of noncoding and repeat [[DNA]] sequences in more complex...

 and Viral replication

Viral replication

Viral replication is the term used by virologists to describe the formation of biological viruses during the infection process in the target host cells. Viruses must first get into the cell before viral replication can occur. From the perspective of the virus, the purpose of viral replication is...

By itself, genomic nucleic acid is infectious

Infectious disease

Infectious diseases, also known as communicable diseases, contagious diseases or transmissible diseases comprise clinically evident illness resulting from the infection, presence and growth of pathogenic biological agents in an individual host organism...

.

Transcription: Subgenomic mRNA

Subgenomic mRNA

Subgenomic mRNAs are essentially smaller sections of the original transcribed template strand. During transcription, the original template strand is usually read from the 3' to the 5' end from beginning to end...

 is present in infected cells.

Antigenicity

Antigenicity

Antigenicity is the ability of a chemical structure to bind specifically with certain products of adaptive immunity: T cell receptors or Antibodies . Antigenicity was more commonly used in the past to refer to what is now known as immunogenicity, and the two are still often used interchangeably...

Cross-reactivity

Cross-reactivity

Cross-reactivity is the reaction between an antibody and an antigen that differs from the immunogen. It is sometimes also referred to as crossimmunity or cross-protective immunity...

  is found. Cross-reactivity between species of the same serotype

Serotype

Serotype or serovar refers to distinct variations within a subspecies of bacteria or viruses. These microorganisms, viruses, or cells are classified together based on their cell surface antigens...

, but not with species of another serotype and some species of the same serotype, but not with all. Although the degree of antigenic specificity varies with the degree of relatedness, the antigenicity is distinct from serogroups of the same genus. Most species in the genus are related antigenically. They are sharing some epitopes in the structural proteins.

External links

• ICTVdB - The Universal Virus Database, version 4. http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/