from what genome does the information come that produces an enveloped virus?
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Structure and Organization of Virus Genomes
This chapter provides an in depth study on the structure, composition, and organization of viral genomes, their classification into double stranded and single stranded DNA viruses, positive and negative stranded RNA viruses with and their genome diversity. ...
Genome and Genomics. 2019 Nov 18 : 1–30.
Published online 2019 Nov 18. doi: 10.1007/978-981-15-0702-1_1
PMCID: PMC7119911
Structure and Organization of Virus Genomes
K. V. Chaitanya2
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Abstract
This chapter provides an in depth study on the structure, composition, and organization of viral genomes, their classification into double stranded and single stranded DNA viruses, positive and negative stranded RNA viruses with and their genome diversity. Segmentation and re-assortment of viral genomes have been discussed along with the multipartite virus genomes. Genome details of 13 different viruses have been provided as type studies for better understanding of these topics. Concepts of viral genome evolution have also been discussed.
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Introduction
A Virus is a small electron microscopic parasite, incapable of reproducing by its own, survives by directing the host cell machinery for the production of more viruses, which emerges from their respective host cell through lysis. Most of these viral organisms contain either double stranded or single stranded DNA as well as RNA in their genomes, which may be either single stranded or double stranded. After the purification and partial crystallization of Tobacco Mosiac Virus in 1935 by Wendell Stanley, the study of viruses has inspired many scientists, which lead to identification and characterization of plant, bacteria, archaea, and animal viruses. Since viruses are capable of infecting a large number of various cell types, genetically modified viruses are being considered for the gene therapy. All these factors and applications make the virus an important organism for its capability to infect any living organism on this planet.
Viruses are small submicroscopic, obligate intracellular parasites, which contains either DNA or RNA as genome protected by a virus-encoded protein coat called capsid. Viruses are mobile genetic elements, depends on metabolic and biosynthetic machinery of host cells for their propagation. Viruses cannot carry out their life sustaining functions outside the host cell. They cannot synthesize proteins as they lack ribosomes and uses the host cell ribosome machinery for translating their mRNA into proteins. Viruses can neither generate nor store ATP but derive the necessary energy and other metabolic functions by parasitizing the host cell for the basic materials such as amino acids, nucleotides, and lipids. Even though the viruses are speculated as a form of proto-life, their inability to survive outside living organisms does not make them as living organisms in the strict sense and it is highly unlikely that they preceded cellular life during the evolution of the earth. Some scientists even speculate that viruses have begun as rogue segments of genetic code which got adapted to a parasitic form of existence. Virions are the complete virus particles that are produced by the assembly of the pre-formed viral components, whose main function is to deliver its genome into the host cell for its expression (transcription and translation). The icosahedral virion belonging to the icosahedral or structural class of viruses is made of 20 identical triangular faces, each face is constructed with three identical capsid protein units making 60 subunits per capsid, with five subunits symmetrically contacting each of the 12 vertices, thus making all proteins in equivalent interaction with each other. The viral genome is packed inside a symmetric protein capsid, composed of either a single or multiple proteins, each of them is encoding a single viral gene. Due to this symmetric structure, viruses could encode all the necessary information for constructing a large capsid using a small set of genes. A capsid along with the enclosed nucleic acid is called a nucleocapsid. In enveloped viruses, the nucleocapsid is surrounded by a lipid bilayer and is studded with a layer of glycoproteins. Often, the nucleic acid is associated with a protein called nucleoprotein. Viruses possess a great diversity with respect to their size. is the largest virus reported with 400 nm in diameter, bigger than the bacteria, which is ~200 to 300 nm long. They also exhibit a wide diversity in shapes and forms, such as spherical, rod-like, etc.
There are few subviral entities which are highly similar, pathogenic and are possessing the properties similar to that of viruses. These entities are viroids, virusoids, and prions. Viroids are a short stretch of highly complementary, single stranded (200–400 nucleotides), circular RNA molecules possessing a rod-like secondary structure without any capsid or envelope. These viroids are associated with plant and human diseases such as hepatitis D. They are obligate intracellular parasites, with replication strategies similar to viruses. Virusoids are a satellite, circular single-stranded RNAs (1000 nucleotides) dependent on plant viruses for replication and encapsidation. They are packed into virus capsids as passengers. Their genome encodes only structural proteins. Prions are anomalous infectious agents that cause fatal neurodegenerative diseases mediated by contemporary mechanisms. Prions consist of a single type of protein molecule without any nucleic acid component. The protein is a modified isoform of prion protein (PrP) designated PrPSc. The normal cellular PrPC is converted into PrPSc by a structural transition of its α-helical and coil structure is refolded into β-sheet. The prion protein and its encoding gene are often found in normal uninfected cells and are associated with viral diseases such as Creutzfeldt–Jakob disease in humans, scrapie in sheep and bovine spongiform encephalopathy (BSE) in cattle.
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what features vary among different types of viruses?
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viruses vary with regard to their structure and their genomes.
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how does the release if HIV resemble exocytosis?
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viral relase occurs as budding process in which a membrane vesicle is formed that surrounds te capsid. similarly exocytosis involves the formation of a membrane vesicle that encloses some type of cargo.
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Terms in this set (58)
what features vary among different types of viruses?
viruses vary with regard to their structure and their genomes.
how does the release if HIV resemble exocytosis?
viral relase occurs as budding process in which a membrane vesicle is formed that surrounds te capsid. similarly exocytosis involves the formation of a membrane vesicle that encloses some type of cargo.
from the perspective of the virus what are the primary advantages of the lytic and lysogenic cycles?
the advantages of the lytic cycle is that a viruss can make many copies of itself and proliferates.However sometimes the growth conditions may not be favorable to make new viruses. thaadvantage of the lysogentic cycle is that the virus can remain latent until conditions become favorable to make new viruses.
How does someone contract a prion disease?
by either eating an animal with the diease, they get the abnormal protein
how many nucleoid regions are in the bacterial cell to the far right
3
how is a nucleoid different from a nucleus found in a eukaryotic cell?
a nucleoid is not a membrane bound organelle. it is simply a region where a bacterial chromosome is found . a cell nucleus in a eukaryotic cell has an envelope with a double membrane,
describe how the loop domains are held in place
the loop domains are held in place by proteins that bind to the DNA at the bases of the loops . the proteins also bind to each other.
describe the similarities and differences between bacterial chromosomes and a plasmid.
bacterial chromosomes and plasmids are similar in that they typically contain circular DNA molecules . However bacterial chromosomes are usually much longer than plasmids and carry many more genes. Also, bacterial chromosomes tend to be more compacted due to the formation of loop domains and supercoiling.
lets suppose a bacterial strain divides every 30 minutes. if a single cell is placed on a plate, how many cells will be in the colony after 16 hours?
16 hours is the same as 32 doubling so 2^32+ 4,294,967,296( the actual number would be much less because the cells would deplete the growth media and grow more slowly than the maximal rate.)
would the reults have been different if the pore size was larger and allowed the passage of bacterial cells?
yes the two strains would have mixed together ,allowing them to conjugate. therefore,there would have been colonies on the plates.
if the donor cell has only one F factor how the donor and recipient cell both contain one f factor following the transfer of an f factor during conjugation.
During conjugation, only one strand of the DNA from an F factor is transferred from the donor to the recipient cell. the single-stranded DNa in both cells is then used as a template to create double stranded F factor DNa in both cells.
how did the phenomenon of transformation allow researchers to demonstrate that DNA is the genetic material ?
Griffiths was abel to show that gentic material was transferred to tyope R bacteria, which converted them to type S. This occurred vis transformation. Later, Avery, macleod and McCarty determined that DNA was the material that was being transferred.
Is transduction a normal part of the phage life cycle?
transduction is not a normal part of the phage life cycle. it is a mistake in which a piece of the bacteria chromosome is packaged into a phage coat and is then transferred to another bacterial cell.
the___ is the protein coat of a virus that surrounds the genetic material
a. host b. prion. c. capsid d. viroid e. capsule c. capsid
among the viruses identified, the charateristics of their genomes show many varriations, which of the following does not describe a typical characteristic of viral genomes?
a. the genetic material may be RNA or DNA
b. the nucleic acid may ne single stranded or double stranded.
c. the genome may carry just a few genes or several dozen.
d. the number of copies of the geome may vary.
e. all of the above describe typical variation on viral genomes.
e. all of the above describe typical variation on viral genomes.
during viral infection, attachment is usually specific to a particular cell type because
a. the virus is attracted to the appropriate host cells by proteins secreted into the extracellular fluid.
b. the virus recognizes and binds to specific molecules in the cytoplasm of the host cell
c. the virus recognizes and binds to specific molecules on the surface of the host cell
d. the host cell produces channel proteins that provide passageways for viruses to enter the cytoplasm.
e. the viruses relases specific proteins that make holes in the membrane large enough for the virus to enter.
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