Why do retroviruses need reverse transcriptase

Endogenous retroviruses are a type of transposon. The virus itself stores its nucleic acid in the form of an mRNA genome and serves as a means of delivering that genome into cells it targets as an obligate parasite a parasite that cannot live without its host. That process of delivering the genome into cells constitutes the infection. It is difficult to detect the virus until it has infected the host, where the provirus can stay for months, even years, before becoming active and making new infectious viral particles.

Retroviruses, however, function differently. Retroviruses can be pathogens of many different hosts, including humans. As well as infecting a host, some retroviruses can cause cancer. HIV viral life cycle : This diagram depicts the viral life cycle of HIV, from infection, integration into a host genome, reconstruction, and formation of new viral particles. The inset on the left depicts an individual HIV particle. Finally, retroviruses are proving to be valuable research tools in molecular biology and have been successfully used in gene delivery systems.

HIV entry is the earliest stage of infection in the HIV viral life cycle, occurring when the HIV virus comes into contact with the host cell and introduces viral material into the cell. HIV enters macrophages and CD4-positive T cells CD4 is a glycoprotein receptor found on cells by the adsorption of glycoproteins on its surface to receptors on the target cell, followed by fusion of the viral envelope with the cell membrane and the release of the HIV capsid into the cell.

Viral DNA is formed by reverse transcription. Virus maturation and protease release of individual HIV proteins. Entry to the cell begins through interaction of the trimeric envelope complex and both CD4 and a chemokine receptor on the host cell on the cell surface.

Shown in purple is gp and in green gp41, two proteins crucial in viral docking to host cells. After attachment, the HIV viron must next fuse with the host cell. The first step in fusion begins after the attachment of the CD4 binding domains of gp to CD4.

Once gp is bound with the CD4 protein, the envelope complex undergoes a structural change, exposing the chemokine binding domains of gp and allowing them to interact with the target chemokine receptor.

This allows for a more stable two-pronged attachment, which allows the N-terminal fusion peptide gp41 to penetrate the cell membrane. Repeat sequences in gp41, known as HR1 and HR2, then interact, causing the collapse of the extracellular portion of gp41 into a hairpin.

This loop structure brings the virus and cell membranes close together, allowing fusion of the membranes and subsequent entry of the viral capsid. After HIV has bound to the target cell, the HIV RNA and various enzymes including reverse transcriptase, integrase, ribonuclease, and protease are injected into the cell. The retroviral genome contains the elements needed for reverse transcription and all other activities of a retrovirus.

The retroviral while in the viral capsid consists of a dimer RNA. The RNA genome also has terminal noncoding regions, which are important in replication, and internal regions that encode virion proteins for gene expression. Gag proteins are major components of the viral capsid, which are about 2,, copies per virion. Protease is expressed differently in different viruses.

New virus particles assemble, exit the cell, and can infect another cell. This image is linked to the following Scitable pages:. How did viruses evolve? Are they a streamlined form of something that existed long ago, or an ultimate culmination of smaller genetic elements joined together? Comments Close. The Comment you have entered exceeds the maximum length. Submit Cancel. Comments Please Post Your Comment. No comments yet. Save Note Note. Save Cancel Delete. This means that, in theory, they can be used to cause the cellular machinery to make proteins in an ongoing way.

For example, scientists have used retroviruses to help diabetic rats make their own insulin. Get information on prevention, symptoms, and treatment to better ensure a long and healthy life.

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Reversal of diabetes through gene therapy of diabetic rats by hepatic insulin expression via lentiviral transduction. Mol Ther. Goldsmith CS. Morphologic differentiation of viruses beyond the family level. Your Privacy Rights. To change or withdraw your consent choices for VerywellHealth. At any time, you can update your settings through the "EU Privacy" link at the bottom of any page. These choices will be signaled globally to our partners and will not affect browsing data.

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