Influenza virus replication Cycle Animation - Medical Microbiology USMLE step 1

Summary

This video explains the process by which the influenza virus infects host cells, from its initial attachment to the host cell through hemagglutinin proteins, to its replication cycle. The virus exploits the cell’s endocytosis mechanism and uses the acidity in the lysosome for uncoating. It describes the 'cap snatching' technique, where the virus hijacks the host's mRNA to replicate itself. The virus assembles new proteins and RNA segments within the cell, eventually forming new viruses that bud from the host's membrane, ready to infect other cells.

Takeaways

• 🦠 The flu is a contagious respiratory infection caused by influenza viruses, which must enter host cells to replicate.
• 🔗 Influenza virus attaches to a host cell using a protein called hemagglutinin, which binds to receptor polysaccharides ending with cyanic acid.
• 🔄 The cell takes up the virus through endocytosis, and the viral particle's acidic environment triggers the uncoating process.
• 💊 Some anti-influenza drugs block the ion channel that allows protons to enter the virus, preventing uncoating.
• 🧬 Hemagglutinin undergoes a structural change, triggering membrane fusion and allowing the viral RNA genome to flow into the cytoplasm.
• 🚪 The viral RNA segments enter the nucleus via nuclear pores, where they are copied into complementary plus strands for protein production.
• 🧢 The virus performs 'cap snatching' by taking a 5' cap from the host's mRNA to start its own viral RNA transcription.
• 🧫 Viral mRNA is translated by the host ribosomes into proteins, including the nucleocapsid and envelope proteins.
• 📦 The newly made RNA segments are packaged into new viruses, which bud off from the cell membrane to infect other cells.
• 🚚 Envelope proteins are transported via vesicles from the endoplasmic reticulum to the Golgi apparatus and then to the plasma membrane.

Q & A

What is the primary cause of the flu?

The flu is caused by influenza viruses, which are contagious respiratory infections.

How does the influenza virus enter a host cell?

The influenza virus enters a host cell by attaching via a protein called hemagglutinin, which binds to a receptor on the host cell's surface, initiating endocytosis.

What role does hemagglutinin play in the infection process?

Hemagglutinin is a viral protein that recognizes and binds to host cell receptors, enabling the virus to enter the cell. It also facilitates membrane fusion during the uncoating process.

How does the virus exploit the host cell's acidity to begin the uncoating process?

The virus uses the acidity inside the endocytic vesicle to disrupt protein-protein interactions, causing matrix proteins to detach from the viral RNA genome, which initiates the uncoating process.

What is cap snatching, and why is it important for the influenza virus?

Cap snatching is a process where the viral RNA polymerase cuts the 5' cap from a host mRNA and uses it to start transcription of viral RNA. This is crucial for making viral mRNA that can be translated by host ribosomes.

Why does the influenza virus need to produce a complementary plus strand of RNA?

The viral RNA genome is a negative-strand RNA, which is non-coding. It must be transcribed into a complementary plus strand before it can be used to make proteins through translation.

How do viral envelope proteins get produced and where are they synthesized?

Viral envelope proteins, such as hemagglutinin, are synthesized by host ribosomes on the endoplasmic reticulum and then transported via vesicles to the Golgi apparatus and plasma membrane.

What happens to the newly synthesized viral RNA and proteins inside the host cell?

The viral RNA segments are combined with RNA polymerase, nucleocapsid proteins, matrix proteins, and packaging proteins. These components are exported from the nucleus and assembled into new virus particles.

How are new virus particles released from the host cell?

New virus particles are assembled and packaged at the host cell's plasma membrane, where they bud off and are released to infect other cells.

What role does the viral ion channel play in the influenza virus infection cycle?

The viral ion channel allows protons to enter the viral particle, which triggers the release of the viral RNA genome by disrupting internal protein interactions, starting the uncoating process.