Lecture 18: Replication of Viruses (Check facts) Flashcards
Monday 18th November
What are the 6 steps of viral replication?
- Attachment
- Penetration
- Uncoating
- Biosynthesis
- Assembly
- Release
How do viruses bind to their cellular recptors?
Through their VAPs. This interaction is very specific and it determines the host cell and the species range.
In enveloped viruses where are the VAPs located?
Within the viral envelope
In naked viruses, where are the VAPs located?
VAPs are located within the capsid
What is viral tropism?
The specificity of a virus to a specific cell or host
Describe step 1 of the replication of viruses
- The virus will adhere to cellular surfaces through random collision.
- The binding is specific, but finding the right receptor is random, not specific.
Describe step 2 of viral replication
- The virus attaches to a specific receptor on the cellular surface, more than one receptor may be involved.
Describe step 3 of viral replication
- The viral genome is released into the cytoplasm
- (or the viral genome may need to be transported into the nucleus)
Describe step 4 of viral replication
-
How many receptors does HIV require for binding to the host cell?
2
What was detected as the receptor for the influenza virus in 1985?
sialic acid
Is it true that different viruses can bind to the same receptors?
Yes
What are some examples of viruses that bind to the same recptor?
Adenovirus and Coxsackievirus B3 bind the same receptor
Is it true that viruses of the same family may bind to different receptors?
Yes
Is it true that one virus may bind to many different receptors?
Yes, one example of this is Herpes Simplexvirus-1 (HSV-1), which can infect different tissues and can interact with and bind to different receptors
What are 2 ways a virus can enter a host cell?
Via phagocytosis and via endocytosis (phagocytosis usually involves the uptake of larger particles, whilst endocytosis involves the uptake of smaller particles, including fluid).
Which viruses enter the host cell by fusing with the plasma membrane?
Enveloped viruses
Why is fusion with the plasma membrane sometimes preferred?
- Easy and quick
- Requires certain fusion proteins, as well as the VAPs
What are some examples of viruses that fuse with the plasma membrane?
HIV, herpes virus
Describe the process of fusion of viruses with the host cell membrane
- The viral attachment proteins on the virus will attach to specific receptors on the host cell plasma membrane.
- After the binding to the receptor, fusion proteins embedded in the viral envelope are activated and undergo conformational changes that lead to changes in the fusion proteins, exposing a fusion peptide that interacts with the host membrane.
- The fusion peptide then exposing a fusion peptide that interacts with the host membrane.
- The virus and host will eventually fuse together, the viral genome will be uncoated, and released into the host cell cytoplasm.
Describe the process of fusion of viruses with the host cell membrane within the cytoplasm
- For the fusion proteins to be activated, the pH has to be lowered.
- The virus binds to specific receptors on the plasma membrane and instead of fusing with thw plasma membrane, is endocytosed.
- The virus is endocytosed and an endosome is formed.
- The endosome is then transported to a low pH area of the cytoplasm.
- Fusion is initiated inside the endosome, uncoated, and the nuclear capsid is released in the cytoplasm.
Describe non-enveloped endocytosis
Non-enveloped viruses bind to specific receptors on the host cell surface using their capsid proteins.
This interaction triggers the host cell to internalise the visu, and so the virus is endocytosed within an endosome.
The endosome and its environment becomes increasingly acidic
Viral proteins poke holes in the endosome through which viral particles enter the cytoplasm
Is it true that microtubules move endosomes/viruses?
Yes
What is uncoating?
The removal of the protein capsid
