Influenza virus replication Cycle Animation - Medical Microbiology USMLE step 1
Summary
TLDRThis 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.
Outlines
🦠 Understanding Influenza Virus Infection
This paragraph provides an overview of the influenza virus, a contagious respiratory infection. It explains that the virus needs to enter host cells to replicate, detailing the process which involves several stages such as attachment, entry, viral RNA, protein production, assembly, and release from the host cell.
🔗 Virus Attachment and Entry
The paragraph describes how an influenza virus attaches to a host cell. It focuses on the role of hemagglutinin, a protein in the viral envelope, which binds to host receptors terminating in sialic acid. Following attachment, the virus is taken up by endocytosis into the cell.
🧬 Fusion with Lysosomes and Acidic Activation
This section explains the role of the endocytic vesicle in fusing with a lysosome, which contains digestive enzymes and has an acidic environment. The virus exploits this acidity using an ion channel to allow protons to enter the virus, which disrupts protein-protein interactions and initiates the uncoating process, separating matrix proteins from the viral RNA genome.
💊 Inhibition by Anti-Influenza Drugs
It is noted that certain anti-influenza drugs can block the ion channel that the virus uses to acidify its interior, thereby preventing the uncoating process and hindering the virus's ability to replicate.
🔄 Membrane Fusion and RNA Release
The paragraph details how the acidity also triggers hemagglutinin to change structure and insert into the vesicle membrane, which leads to membrane fusion. This process allows the RNA genome and associated proteins to enter the cytoplasm, completing the uncoating process.
🏗️ RNA Genome Structure and Transport
Here, the structure of the influenza virus's RNA genome is described. The eight RNA segments, which are negative-strand RNAs, are covered with nucleocapsid proteins and attached to viral RNA polymerase. These RNA-protein units enter the nucleus through nuclear pores for replication and transcription.
🧪 Cap Snatching for mRNA Synthesis
The virus synthesizes new viral mRNAs by a method called 'cap snatching', where it cuts off the cap from the host's mRNA molecules and uses it to start the transcription of its own viral RNA. This process is crucial for stabilizing the viral mRNA and ensuring its translation by host ribosomes.
🔬 Viral Protein Synthesis in Cytoplasm
This paragraph covers the translation of viral mRNA into proteins in the cytoplasm by host ribosomes. It highlights how different mRNAs code for various viral proteins, including nucleocapsid and envelope proteins, essential for viral replication and assembly.
🌐 Envelope Protein Production and Transport
It describes the production of envelope proteins, such as hemagglutinin, in the endoplasmic reticulum of the host cell. These proteins are transported via vesicles to the Golgi apparatus and eventually to the plasma membrane.
📦 Packaging of Viral RNA and Proteins
The newly synthesized viral RNA and proteins, including nucleocapsid and matrix proteins, are assembled in the nucleus. The fully formed RNA genome segments and associated proteins are then exported from the nucleus to be packaged into progeny viruses.
🧫 Assembly and Budding of New Viruses
This final paragraph explains the last steps of viral replication, where RNA-protein complexes are packaged into new viruses. These progeny viruses bud from the host cell's plasma membrane, ready to infect new cells and propagate the infection.
Mindmap
Keywords
💡Influenza Virus
💡Hemagglutinin
💡Endocytosis
💡Uncoding Process
💡RNA Genome
💡Cap Snatching
💡RNA Polymerase
💡Nucleocapsid Protein (NP)
💡Envelope Proteins
💡Viral Assembly
Highlights
The flu is caused by influenza viruses, which must enter host cells to replicate.
Influenza virus uses hemagglutinin, a protein, to bind to host cell receptors and gain entry via endocytosis.
After entering the cell, the virus exploits the lysosome's acidic environment to begin uncoating.
An ion channel allows protons to enter the virus, disrupting protein-protein interactions and starting the uncoating process.
Anti-influenza drugs can block this ion channel, preventing the virus from exploiting the acidity.
Hemagglutinin undergoes a structural change, allowing it to fuse with the vesicle membrane and complete the uncoating.
The viral RNA genome, along with nucleocapsid proteins, enters the host nucleus to begin replication.
Influenza RNA is non-coding (- strand) and needs to be copied into complementary (+ strand) RNA for protein translation.
The virus performs 'cap snatching,' stealing the 5' cap from host mRNA to start viral RNA transcription.
The viral mRNA receives a poly-A tail for stability before leaving the nucleus for protein translation.
Viral envelope proteins like hemagglutinin are synthesized by the host's endoplasmic reticulum.
Newly made nucleocapsid proteins stabilize viral RNA strands, aiding in the production of additional viral genomes.
Full-length minus strands of RNA are synthesized to serve as the genome segments of new viruses.
Ten different proteins are synthesized from eight RNA segments, and new viral genome segments are exported from the nucleus.
New viruses are assembled and bud off from the host cell membrane, completing the viral replication cycle.
Transcripts
[Music]
the flu is a contagious respiratory
infection caused by influenza viruses
like all viruses influenza must gain
entry into host cells to replicate the
process involves several stages from
attachment and entry to viral RNA and
protein production to assembly and
release from the host cell
an influenza virus attaches to a cell
when hemagglutinin one type of protein
in its viral envelope binds to a host
receptor hemagglutinin recognizes
receptor polysaccharides that terminate
with cyanic acid the cell then takes up
the virus by endocytosis
the endo siddik vesicle then fuses with
a lysosome a lysosome contains digestive
enzymes and an acidic interior and
typically digests contents taken in from
outside the cell
unfortunately for the host the virus
uses the acidity to its advantage an ion
channel allows protons to enter the
virus the acidity inside the viral
particle disrupts protein-protein
interactions causing matrix proteins to
detach from proteins covering the viral
RNA genome this detachment is the
beginning of the un-- coding process
it's interesting to note that one type
of anti influenza drug blocks this ion
channel
the acidity also triggers hemagglutinin
to make a structural change and insert
itself into the vesicle membrane in this
new form hemagglutinin stimulates
membrane fusion the RNA genome and
associated proteins can flow freely away
from the matrix proteins into the
cytoplasm completing the uncoding
process
viii RNA segments of the influenza
genome are covered with nucleo capsid
proteins abbreviated NP and attached to
several other proteins that make up the
viral RNA polymerase these RNA protein
units enter the nucleus via the nuclear
pores
the RNA segments are - strand rnase
meaning that they're non-coding strands
each of the eight segments needs to be
copied into a complementary plus strand
by the viral RNA polymerase before it
can be used for translating proteins
to make a messenger RNA for translation
by host ribosomes the virus needs to add
a structure called a five prime cap at
the beginning of the mRNA transcript the
virus performs a stealthy act known as
cap snatching in which the viral RNA
polymerase cuts off the cap from one of
the host cells own mRNA molecules and
uses the cap to start transcription of
viral RNA the new plus strand viral RNA
gets a poly a tail that aids in mRNA
stability
the new viral mRNA leaves the nucleus
for the cytoplasm where the host cells
ribosomes translate the mRNA in this
example the mRNA codes for the nucleo
capsid protein that will code future
viral RNA molecules
several other mRNAs code for viral
envelope proteins envelope proteins are
made by ribosomes on the host cells
endoplasmic reticulum this particular
mRNA codes for hemagglutinin
back in the nucleus the newly made
nucleo capsid proteins prime and
stabilized viral RNAs as they're being
synthesized into full-length + strands
this time lacking a cap and a poly a
tail newly made RNA polymerase proteins
enter the nucleus and participate in the
production of additional full-length
minus strands that will serve as the RNA
genome segments of new viruses
from these events 10 different types of
proteins are synthesized from 8 RNA
segments and new minus strand RNA genome
segments are produced the RNA genome
segments complex with RNA polymerase
nucleo capsid proteins matrix protein
and packaging proteins are exported from
the nucleus
the envelope proteins made on the
endoplasmic reticulum moved by transport
vesicles from the endoplasmic reticulum
to the Golgi apparatus and finally to
the plasma membrane the RNA protein
complexes are then packaged into progeny
viruses as they bud from the cell
membrane
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