By using this form you agree with the storage and handling of your data by this website. Animal Cells Prokaryotic Cells Vs. Eukaryotic Cells Amphibians Vs. Reptiles Anatomy Vs. Physiology Diffusion vs. Osmosis Mitosis Vs. Meiosis Chromosome Vs. Bio Explorer. Suggested Reading: How do viruses reproduce? Virus Life Cycle. Hepatitis B Virus Life Cycle Source: Wikimedia The life cycle of the virus is a series of steps that enable the virus to infect a host and replicate itself.
Nucleic acid. These strands are used as a template for transcription and translation for the synthesis of proteins, using host cell machinery, and can be either plus strands positive or coding strand or minus strands negative strand or non-coding strand.
In case of the presence of a negative single-stranded RNA as genetic material, some viruses contain a transcriptase enzyme to transcribe genetic material into its complementary coding form, ready for protein synthesis. Viruses can be classified based on their genetic content, which is discussed further on in this article. The size of the nucleic acid content or genome of viruses ranges from kb.
Some viruses develop further structures on the envelope like spikes that aid the virus during the infection process. The proteins in the envelope help to attach to cell surface receptors of the host cell as well as, fusion and entry of the viral particle into the host cell. Apart from these, the envelope contains matrix proteins that help it to be attached to the nucleocapsid.
Enzymes and proteins required in the viral life cycle can also be found in the envelope. TMV Virus Structure Source: Wikimedia Viruses with the helical structure are composed of capsomeres that are identical to each other, and are typically arranged around a central axis, which gives it a helical form.
Poliovirus Structure Source: Wikimedia Essentially, an icosahedral shape is formed by the fusion of many equilateral triangles spherically.
Geometrically, an icosahedral shape has 12 corners or vertices, 20 sides or equilateral triangles and 30 edges. There can be two types of icosahedral capsids — hexagonal at the vertices or pentagonal at the vertices. Head or Tail. Complex or Asymmetrical. Poxvirus Structure Source: Wikimedia The complex morphological type consists of viruses whose capsid is neither helical nor icosahedral and may be asymmetric. But the last one viral envelope is present mainly in the animal virus structure.
Viruses vary greatly in their size, ranging from approximately kb Papovaviridae, Parvoviridae, etc. Different structures of virus genomes are given below. Single-stranded linear structure: These single-chain genomes can be positive-sense single-stranded RNA or negative-sense single-stranded RNA or ambisense. In an Ambisense virus , some part of genome is sense strand and some part is the antisense.
The genome of some RNA viruses is segmented, which means that a virus particle contains several different RNA molecules, like different chromosomes. Protein capsid is an essential component of virus structure. Viral genomes are surrounded by shells of proteins known as capsids. A capsid is composed of repetitive structural subunits that are arranged in one of two symmetrical structures, a helix or an icosahedron. However, in many cases, these structural subunits also called protomers are made up of various polypeptides.
The detail of helical and icosahedral virus structures is described below. This protein is arranged in a helix around the viral RNA, with 3 nucleotides of RNA fitting into a groove in each subunit. The helical capsids can also be more complex as they involve more than one protein subunit.
A Helix can be defined by two parameters, its diameter, and pitch. This structure is very stable and can be easily disassociated and re-associated by changing the ionic strength, pH, temperature, etc.
The interactions that hold these molecules together are not covalent and involve H bonds, salt bridges, hydrophobic interactions, and Vander Waals forces. Several families of animal viruses contain helical nucleocapsids, for example, Orthomyxoviridae influenza , Rhabdoviridae rabies and Paramyxoviridae bovine respiratory syncytial virus.
A virus cannot replicate alone. Viruses must infect cells and use components of the host cell to make copies of themselves. Often, they kill the host cell in the process, and cause damage to the host organism.
Viruses have been found everywhere on Earth. Researchers estimate that viruses outnumber bacteria by 10 to 1. Viruses are submicroscopic, which means that you cannot see them in the microscope.
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