HIV Life Cycle | HHMI BioInteractive Video

Summary

The script explains the life cycle of HIV, a retrovirus that targets T helper cells via CD4 receptors. It details the virus's entry into cells, the conversion of its RNA to DNA by reverse transcriptase, and subsequent integration into the host genome by integrase. The script also covers the production of viral proteins, assembly, and maturation, leading to the release of new virions to infect more cells, perpetuating the infection.

Takeaways

• 🌐 HIV is a retrovirus with an outer envelope and contains two copies of RNA and an enzyme called reverse transcriptase.
• 🔒 The virus infects T helper cells by binding to the CD4 receptor and the chemokine coreceptor (CCR5), leading to a conformational change and membrane fusion.
• 🧬 Reverse transcriptase converts viral RNA into DNA, introducing errors due to its poor proofreading activity.
• 🔄 The single-stranded DNA is further reverse transcribed into double-stranded DNA by the same enzyme.
• 🚀 Integrase carries the double-stranded DNA into the nucleus, where it inserts into the host chromosome, establishing lifelong infection.
• 📜 RNA polymerase transcribes viral RNA, which encodes for various viral proteins that are essential for the virus's structure and function.
• 🛠️ Viral proteins, including the envelope protein, are synthesized and processed through the rough endoplasmic reticulum and Golgi apparatus.
• 🔗 The envelope protein is embedded in the cellular membrane, where it coalesces with other proteins to form a cluster on the cell surface.
• 🌱 Additional viral proteins and RNA are assembled at the cell surface, and the immature virion buds off.
• ⚒️ Protease digests the polyprotein chains, allowing the virus to mature and become infectious, ready to infect other cells.

Q & A

What is a retrovirus and how does HIV fit into this category?

A retrovirus is a type of virus that has an outer envelope and contains two copies of RNA and an enzyme called reverse transcriptase. HIV, or Human Immunodeficiency Virus, is a retrovirus because it shares these characteristics, using reverse transcriptase to convert its RNA into DNA.

How does HIV specifically infect T helper cells?

HIV infects T helper cells by binding to the CD4 molecule, a surface receptor exclusive to these cells. This interaction causes a conformational change that allows a second receptor, the chemokine coreceptor (CCR5), to bind, leading to the fusion of viral and host cell membranes and the injection of viral genetic material.

What is the role of reverse transcriptase in the HIV life cycle?

Reverse transcriptase plays a crucial role in the HIV life cycle by converting viral RNA into a single strand of DNA using host nucleotides. It then converts this single-stranded DNA into double-stranded DNA, which is essential for the virus to integrate into the host genome.

What errors does reverse transcriptase typically make during the transcription process?

Reverse transcriptase is known for making random errors during the transcription process due to its poor proofreading activity. This lack of accuracy contributes to the high mutation rate of HIV, which helps it evade the host's immune system.

How does integrase facilitate the integration of HIV DNA into the host chromosome?

Integrase, an enzyme that comes with the virus, grabs the double-stranded DNA and carries it through a nuclear pore into the cell's nucleus. It then makes a nick in the host DNA, allowing HIV to insert itself into the host chromosome, which establishes a lifelong infection.

What is the function of the viral envelope protein?

The viral envelope protein serves as a key component in the infection process. It binds to the CD4 receptor and the chemokine coreceptor on T helper cells, leading to membrane fusion. After the viral genetic material is injected into the cell, the envelope protein remains on the cell surface.

How are viral proteins produced and assembled into new virions?

Viral proteins are produced through the translation of messenger RNAs that are transcribed from the integrated viral DNA. These proteins are then transported to the cell surface where they coalesce with envelope proteins. Along with RNA and enzymes, they form a complex that buds off the cell surface. Protease, another viral enzyme, digests the polyprotein chains, allowing the formation of mature virion structures.

What is the role of RNA polymerase in the production of new viral components?

RNA polymerase is responsible for transcribing the integrated viral DNA into messenger RNA. These mRNAs encode for different viral proteins, which are then translated by ribosomes at the rough endoplasmic reticulum, leading to the production of new viral components.

How does the process of budding lead to the release of new virions from the infected cell?

Budding is the process where the newly formed viral components, including RNA, proteins, and enzymes, coalesce at the cell surface and pinch off, forming a new virion. This budding occurs at the cell membrane, and the newly formed virions are released to potentially infect other cells.

Why is the maturation of the viral particle by protease essential for its infectivity?

The maturation process by protease is essential because it cleaves the polyprotein chains into their functional components, allowing the formation of the mature virion structures necessary for infectivity. Without this step, the virus would not be able to infect new cells effectively.