Tobacco Mosaic Virus and Electron Microscopy

Questions and Answers

What major technological advancement in the 1930s contributed to the study of viral structures?

Invention of X-ray crystallography

Advancement of electron microscopy (correct)

Development of radioisotope labeling

Development of fluorescence microscopy

Which scientist is recognized for obtaining bacilliform particles of tobacco mosaic virus in crystalline form?

Errel

Tuort

Akhmatulina

Stanley (correct)

What significant contribution did bacteriophages make to the field of virology?

They helped establish virology as an independent science. (correct)

They confirmed that all viruses contain nucleic acids.

They provided the first evidence of viral pathogenesis.

They were the first viruses discovered in plants.

Which Kazakhstani scientist is recognized as the founder of virology in Kazakhstan?

H.J.Zhumatov Signup and view all the answers

What aspect of modern science has significantly advanced the understanding of viral genomes?

Development of molecular biology methods Signup and view all the answers

What type of models were developed based on phytovirus virions as a potential vaccine strategy?

Chimeric phytoviruses Signup and view all the answers

What significant contribution did D.I. Ivanovsky make to the field of virology?

He was the first to identify a virus as a distinct form of life. Signup and view all the answers

Which painting style provided evidence of the viral disease of tulips in ancient times?

17th century Dutch art showcasing flowers. Signup and view all the answers

What process did Dutch tulip breeders use to try to create extraordinary flowers?

Grafting healthy solid-colored tulips with striped ones. Signup and view all the answers

What did Adolf Mayer discover about the tobacco mosaic disease in his research?

The signs of mosaic can be obtained by injecting the juice of infected plants. Signup and view all the answers

What property of tobacco mosaic virus was demonstrated by D.I. Ivanovsky in his dissertation?

The virus can be filtered through bacterial filters. Signup and view all the answers

What delayed the recognition of D.I. Ivanovsky's discovery in the scientific community?

Martin Beyerink's research confirming Ivanovsky's conclusions came later. Signup and view all the answers

What unique feature allows viruses to reproduce?

They reproduce exclusively in the cells of other organisms. Signup and view all the answers

Why are viruses considered to be strict intracellular pathogens?

They cannot grow outside a host cell or on artificial nutrient media. Signup and view all the answers

What characteristic of viruses supports the conclusion that they are living organisms?

Their capacity for replication using host cell machinery. Signup and view all the answers

What type of variability do temperature-sensitive mutants of cucumber green mottle mosaic virus represent?

Genotypic variability. Signup and view all the answers

How do environmental factors primarily influence viruses?

They are affected mainly through the host organism. Signup and view all the answers

What process is used to determine the replication levels of viruses in living organisms?

Filtering methods. Signup and view all the answers

What results from the interaction of viruses with different environmental conditions?

They show adaptability and variability. Signup and view all the answers

How is the ecological niche of a virus primarily determined?

By the range of its potential hosts. Signup and view all the answers

What main components compose a virion?

Nucleic acid and a protein shell Signup and view all the answers

What shape do isometric viruses typically have?

Icosahedral Signup and view all the answers

How does the size of isometric viruses typically compare to that of filamentous viruses?

Isometric viruses have a smaller diameter than filamentous Signup and view all the answers

What is the diameter range of the hollow channel found in the tobacco mosaic virus (TMV)?

4 nm Signup and view all the answers

Which protein structure is characteristic of rod-shaped and filamentous viruses?

Spiral protein shells Signup and view all the answers

What information can be derived from the position of the leaky UAG codon in the TMV’s polymerase ORF?

It suggests evolutionary significance Signup and view all the answers

What is the step size of the helix structure in Tobacco Mosaic Virus (TMV)?

2.3 nm Signup and view all the answers

How many subunits are present in a Tobacco Mosaic Virus particle?

2130 Signup and view all the answers

Which of the following viruses has bacilliform particles?

Alfalfa mosaic virus Signup and view all the answers

What is the molecular mass of the Tobacco Mosaic Virus particle?

39.4·10^6 Signup and view all the answers

What type of symmetry do the protein shells of spherical viruses exhibit?

Icosahedral symmetry Signup and view all the answers

Which of the following statements about the cucumber mosaic virus (CMV) is true?

Its protein envelope consists of 180 subunits grouped into 32 capsomeres. Signup and view all the answers

What components are specifically indicated per dry weight in the composition of viral particles?

Nucleic acid content Signup and view all the answers

What type of genomes can be present in viruses?

Single-stranded and double-stranded nucleic acids Signup and view all the answers

What is the average molecular weight of nucleic acids in most phytoviruses?

$2.0 imes 10^6$ Signup and view all the answers

Which structural feature is common in the envelopes of most plant viruses?

Cylindrical or spherical protein sheaths Signup and view all the answers

What is the role of nucleic acid in viruses?

Encoding genetic information Signup and view all the answers

Which amino acids are found in higher content in the proteins of phytoviruses compared to those in other organisms?

Serine and threonine Signup and view all the answers

What is required for a virus with a fragmented genome to perform infection?

Complete set of viral particles Signup and view all the answers

What is the typical size range of phytovirus protein molecules?

150 to 600 or more amino acid residues Signup and view all the answers

Study Notes

Historical Context of Viral Diseases

Tulip variegation, a viral disease, was recognized in ancient times and depicted in 17th-century Dutch paintings.
Monochrome tulips were less valued compared to variegated ones, indicating a historical appreciation for viral traits in plants.
Dutch breeders experimented with grafting to produce unique tulip varieties by combining healthy and infected plants.

Foundations of Virology

Tobacco mosaic disease was one of the first viral diseases studied extensively.
In 1886, Adolf Mayer established that the mosaic symptoms in tobacco resulted from injecting infected plant juice into healthy plants.
Mayer initially hypothesized that the pathogen was bacterial and noted the loss of infectivity upon boiling.

Key Discoveries in Virology

D.I. Ivanovsky's research in 1892 identified viruses as new infectious agents, detailing properties such as infectivity and filterability.
Ivanovsky described intracellular inclusions known as X-bodies, still relevant for diagnostics today.
Martin Beyerinck’s 1898 research confirmed Ivanovsky's findings, gaining acceptance for the existence of viruses.

Advancements in Virus Research

The introduction of electron microscopy in the 1930s allowed for in-depth analysis of virion structure.
Stanley obtained crystalline particles of the tobacco mosaic virus in 1935, enhancing understanding of viral morphology.
The ability of purified viral nucleic acids to induce infections was demonstrated, cementing DNA and RNA's importance in virology.

Emergence of Virology as a Science

The discovery of bacteriophages led to the establishment of virology as an independent field of study.
Notable virologists contributed to the field, including Mathews, Hull, Jones, Maramorosch, Ryzhkov, and Sukhov among others.

Phytovirology in Kazakhstan

Academician H.J. Zhumatov is recognized as the founder of virology in Kazakhstan.
Prominent Kazakh scientists made significant contributions, including N.B. Akhmatulina and U. Abenova in general virology.
Research addressed viral diseases affecting potatoes, cereals, and industrial crops in Kazakhstan.

Molecular Biology and Viral Research

Advances in molecular biology led to decoding the genomes of various viruses, facilitating the development of genetically engineered vaccines.
Effective diagnostic test systems for phytoviruses were developed, improving management strategies.

Characteristics and Attributes of Viruses

Viruses are obligate intracellular parasites, replicating only within host cells and lack cellular structure.
They possess either RNA or DNA, are dependent on host cellular mechanisms for reproduction, and do not grow on artificial media.
Viral infectivity is attributed to nucleic acid, with protein envelopes providing protection.

Variability and Adaptation in Viruses

Viruses display both genotypic (hereditary changes) and phenotypic (observable traits) variability, adapting to environmental conditions through their hosts.
Different strains of viruses exhibit varied pathogenic effects depending on host types, illustrating the complexity of virus-host interactions.

Evolution of Viruses

Each virus has a specific ecological niche with a defined host range, adapting dynamically to changes in hosts.
Natural selection drives the evolution of viruses, reinforcing their characteristics as living organisms when in host cells, despite showing non-living properties outside.

Structure and Morphology of Virions

Phytopathogenic viruses exhibit various morphologies: rod-shaped, filamentous, isometric (close to spherical), bacilliform, and bullet-shaped.
Virions consist mainly of nucleic acid encased in a protein shell called a capsid, which dictates the virus's shape.
Capsids vary in structure: rod-shaped and filamentous viruses have spiral protein shells, while isometric viruses possess icosahedral shells.
Size of virions varies considerably:
- Isometric viruses: 17-75 nm in diameter.
- Rod-shaped, filamentous, and bacilliform viruses: lengths of several tens to 2000 nm, with diameters of 3-10 nm (filamentous and rod-shaped) and 18-75 nm (bacilliform).

Particles with Spiral Symmetry

Tobacco mosaic virus (TMV) is a well-studied example, measuring 300 nm in length with a central hollow channel of 4 nm diameter.
The RNA of TMV is embedded within a protein envelope, with protein subunits stacked in a helical arrangement.
TMV structure reveals:
- 2130 protein subunits and 6340 nucleotides of single-stranded RNA.
- Molecular mass: TMV particle (39.4 x 10^6), viral RNA (2.05 x 10^6).
Other bacilliform viruses exhibit a similar structure but may differ in helix dimensions.

Particles with Icosahedral Symmetry

Isometric virions appear polyhedral under electron microscopy, comprised of protein subunits (capsomeres) typically arranged as pentamers or hexamers.
Icosahedron structure: 12 vertices, 20 faces, and 30 edges.
Cucumber mosaic virus (CMV) serves as an example, containing 180 subunits in 32 capsomeres and a diameter of 30 nm.

Bacilliform and Bullet-Shaped Particles

Bacilliform and bullet-shaped viruses exhibit elongated forms rounded at both ends or at one end, respectively.
Alfalfa mosaic virus is bacilliform, with lengths varying from 28 to 58 nm and a thickness of 18 nm.
Complex structures may include viruses like potato yellow dwarfism virus, with multilayered envelopes.

Chemical Composition of Viruses

Viruses consist mostly of proteins, with complex viruses containing lipids up to 20% of their weight.
Water constitutes 10-50% of viral particle weight, not included in the analysis of nucleic acid and dry weight components.
Viruses may contain metal ions and polyamines (about 1%).
Nucleic acids carry genetic information, existing as single-stranded or double-stranded RNA/DNA, and may consist of one or multiple molecules.
Nucleic acid molecular weights vary significantly, typically averaging around 2 x 10^6 for most phytoviruses.

Protein Composition

Proteins in phytoviruses share amino acid composition with other organisms but have higher serine and threonine content.
Molecular mass of protein subunits varies from 10 to 18 thousand, with sizes ranging from 150 to over 600 amino acid residues.

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Description

Explore the significant discoveries related to the Tobacco Mosaic Virus (TMV), particularly focusing on the advancements made through electron microscopy in the 1930s. This quiz covers important studies conducted by researchers like Stanley, Girer, and Schram, which enhanced our understanding of viral structures and their nucleic acids.