Microbiology
Summary
The viral lifecycle of HIV involves numerous stages, primarily attacking the host's CD4+ immune cells, including macrophages and helper T-cells. Three significant structural genes are central to this process: gag, env, and pol. These genes are crucial as they encode the components of the virion and vital viral enzymes. The virus enters a host cell through the mediation of the HIV's envelope glycoproteins, in particular through the attachment of gp120 to the CD4 receptor and CCR5 or CXCR4 coreceptors on the host cell's surface.
Once inside, HIV uses its reverse transcriptase enzyme to convert its single-stranded RNA genome into double-stranded DNA. The enzyme integrase then integrates the newly formed viral DNA into the host cell genome. This incorporation into host DNA is irreversible: the host cell will be infected for the rest of its life. Furthermore, the host cell machinery is tricked into transcribing and translating the viral genome. The env gene product, the precursor polyprotein gp160 is processed into gp120 and gp41 in the endoplasmic reticulum and Golgi apparatus. The immature virus then buds off the host cell membrane, forming the viral envelope. HIV protease then cleaves most viral polyproteins into functional proteins, forming mature virions. Despite the host forming neutralizing antibodies, primarily targeting gp120, HIV cleverly combats this response through antigenic variation and dense glycosylation of gp120. To prevent this virus from damaging the immune system, all patients with HIV should be on antiretroviral therapy (ART), with drugs designed to intercept specific parts of the life cycle.
Lesson Outline
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FAQs
HIV (human immunodeficiency virus) belongs to the Retroviridae family of viruses. This family is characterized by their replication process, which involves the conversion of RNA into DNA, facilitated by the enzyme reverse transcriptase. HIV follows this same process within its life cycle, making it a part of the Retroviridae family.
HIV specifically targets CD4+ immune cells, largely T-helper cells, which play a crucial role in our body's immune response. HIV targets these cells because of their surface receptors that allow the virus to bind and integrate itself into the genetic structure of the cell, which gives HIV the ability to replicate and spread through the body.
HIV reverse transcriptase, integrase, and protease are crucial enzymes involved in the HIV life cycle. Reverse transcriptase allows HIV to convert its RNA into DNA once inside a host cell. This DNA is then integrated into the host cell's genome with the help of integrase. Protease works later in the life cycle to cut viral polyproteins into functional proteins, forming mature virions that can go on to infect new host cells.
HIV envelope glycoproteins, namely gp41 and gp120, are crucial components in the virus's life cycle as they mediate the process of viral entry into host cells. Gp120 binds to CD4 receptors on the surface of target cells, often helper T-cells and macrophages. This interaction triggers a conformational change in gp120, exposing the hidden gp41 region. Gp41 then facilitates the fusion of the viral envelope with the host cell membrane, allowing the virus to enter and establish infection.
Genes crucial for HIV's replication include gag, pol, and env. The gag gene encodes for structural proteins, including the matrix, capsid, and nucleocapsid. The pol gene encodes enzymes like reverse transcriptase, integrase, and viral protease. The env gene encodes for envelope glycoproteins, such as gp120 and gp41, which facilitate viral entry into host cells by interacting with cellular receptors.
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