How can virus replicate

Download Virus replication. Bitesize category Pathogens and Disease. Related Articles Virus replication. Viruses: Introduction. Ulcerative colitis and Trichuris infection. Microbial infection in cystic fibrosis. Pathogenic Yersiniae. Immune responses to viruses. Intestinal nematode parasites: mechanisms of resistance. Immune responses to fungal pathogens. Immune responses to bacteria. Chlamydia Trachomatis. Learning Objectives List the steps of viral replication and explain what occurs at each step.

Key Points Viral replication involves six steps: attachment, penetration, uncoating, replication, assembly, and release. During attachment and penetration, the virus attaches itself to a host cell and injects its genetic material into it. During release, the newly-created viruses are released from the host cell, either by causing the cell to break apart, waiting for the cell to die, or by budding off through the cell membrane. Key Terms virion : a single individual particle of a virus the viral equivalent of a cell glycoprotein : a protein with covalently-bonded carbohydrates retrovirus : a virus that has a genome consisting of RNA.

Steps of Virus Infections A virus must use cell processes to replicate. As a result, the virus is engulfed. RNA and proteins are made and assembled into new virions. Attachment A virus attaches to a specific receptor site on the host cell membrane through attachment proteins in the capsid or via glycoproteins embedded in the viral envelope.

Entry The nucleic acid of bacteriophages enters the host cell naked, leaving the capsid outside the cell. Replication and Assembly The replication mechanism depends on the viral genome. Egress The last stage of viral replication is the release of the new virions produced in the host organism.

Other protease cleavage events involved in maturation are less closely controlled. Influenza A virus hemagglutinin must be cleaved into two fragments HA 1 and HA 2 to be able to promote membrane fusion during infection.

Cellular trypsin-like enzymes are responsible for this process, which occurs in secretory vesicles as the virus buds into them prior to release at the cell surface; however, this process is controlled by the virus M2 protein, which regulates the pH of intracellular compartments in influenza virus-infected cells. For lytic viruses most nonenveloped viruses , release is a simple process — the infected cell breaks open and releases the virus. The reasons for lysis of infected cells are not always clear, but virus-infected cells often disintegrate because viral replication disrupts normal cellular function, for example, the expression of essential genes.

Many viruses also encode proteins that stimulate or in some cases suppress apoptosis, which can also result in release of virus particles. Enveloped viruses acquire their lipid membrane as the virus buds out of the cell through the cell membrane, or into an intracellular vesicle prior to subsequent release.

Virion envelope proteins are picked up during this process as the virus particle is extruded. This process is known as budding. As mentioned earlier, assembly, maturation, and release are usually simultaneous processes for viruses which are released by budding. The release of mature virus particles from their host cells by budding presents a problem in that these particles are designed to enter, rather than leave, cells.

Certain virus envelope proteins are involved in the release phase of replication as well as in receptor binding. The best-known example of this is the neuraminidase protein of influenza virus. In addition to being able to reverse the attachment of virus particles to cells via hemagglutinin, neuraminidase is also believed to be important in preventing the aggregation of influenza A virus particles and may well have a role in virus release. In addition to using specific proteins, viruses which bud have also solved the problem of release by the careful timing of the assembly-maturation-release pathway.

Although it may not be possible to separate these stages by means of biochemical analysis, this does not mean that spatial separation of these processes has not evolved as a means to solve this problem. National Center for Biotechnology Information , U. Encyclopedia of Virology. Published online Jul Guest Editor s : Brian W. Guest Editor s : Marc H. Author information Copyright and License information Disclaimer. University of Leicester, Leicester, UK.

All rights reserved. Elsevier hereby grants permission to make all its COVIDrelated research that is available on the COVID resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source.

Abstract In general terms, virus replication involves three broad stages which are present in all viruses: initiation of infection, replication and expression of the genome, and the release of mature virions from the infected cell. Open in a separate window. Figure 1. Entry Entry of the virus particle into the host cell normally occurs a short time after attachment of the virus to the receptor.

Three main mechanisms are observed: 1. Uncoating Uncoating describes the events which occur after host cell entry, during which the virus capsid is partially or completely degraded or removed and the virus genome exposed, usually still in the form of a nucleic acid—protein complex.

Transcription and Genome Replication The replication strategy of a virus depends, in large part, on the structure and composition of its genome. Group II: Single-Stranded DNA The replication of these virus genomes occurs in the nucleus, involving the formation of a double-stranded intermediate which serves as a template for the synthesis of new single-stranded genomes.

The first step in the replication of these viruses e. Monocistronic mRNAs for each of the virus genes are produced by the virus transcriptase in the virus particle from the full-length virus genome. Assembly During assembly, the basic structure of the virus particle is formed as all the components necessary for the formation of the mature virion come together at a particular site in the cell. Maturation Maturation is the stage of the replication cycle at which virus particles become infectious.

Release For lytic viruses most nonenveloped viruses , release is a simple process — the infected cell breaks open and releases the virus. Further Reading Cann A. Elsevier; Amsterdam: Principles of Molecular Virology. HIV-1 and the host cell: An intimate association. Trends in Microbiology. How do animal DNA viruses get to the nucleus? Annual Review of Microbiology. Multistep entry of rotavirus into cells: A Versaillesque dance.

The CCR5 and CXCR4 coreceptors — central to understanding the transmission and pathogenesis of human immunodeficiency virus type 1 infection. Picornavirus—receptor interactions. Cellular receptors for viruses: Links to tropism and pathogenesis. Journal of General Virology. Assembly The stage of replication during which all the structural components come together at one site in the cell and the basic structure of the virus particle is formed.

Attachment The binding of a virus particle to a specific receptor on the surface of a host cell. Capsid A protein shell comprising the main structural unit of a virus particle.

Envelope A lipid membrane enveloping a virus particle. Fusion protein The protein s on the surface of a virus particle responsible for fusion of the virus envelope with cellular membranes.

Gene expression An important stage of viral replication at which virus genetic information is expressed: one of the major control points in replication. Genome replication The stage of viral replication at which the virus genome is copied to form new progeny genomes.

Matrix protein A structural protein of a virus particle which underlies the envelope and links it to the core. Maturation The stage of viral replication at which a virus particle becomes infectious. Molecular epidemiology The use of nucleotide sequence information to study the diversity and distribution of virus populations. Nucleocapsid The core of a virus particle consisting of the genome plus a complex of proteins. Penetration The stage of viral replication at which the virus genome enters the cell.

Polyprotein A long polypeptide encoding several mature proteins which are subsequently released by protease cleavage. Receptor A specific molecule on the surface of a cell which is used by a virus for attachment. Release The stage of viral replication at which virus particles escape the infected cell.

Tropism The ability of a virus to infect specific cell or tissue types. Uncoating The stage of viral replication at which structural proteins are lost and the virus genome is exposed to the replication machinery.