Lecture 4 Flashcards
1
Q
Cell-to-cell transmission strategies
A
- contact via actin based extensions called filopodia
- Virological synapses and membrane nanotubes: small region of close contact between neighbouring cells that allows passage of enveloped viruses from one cell to another
- Formation of syncytia: fusion of infected and uninfected cells
- Intracellular channels like plasmodesmata
2
Q
General Steps in Virus Entry
A
- Attachment: virions attaching to host cell receptors
- Entry: specialized vesicles, penetration of cell membranes
- Transport: localization to target site
- Uncoating: viral genome released into the cell
3
Q
Entry of enveloped viruses
A
- Fusion and fission of the envelope with the plasma membrane
- Receptor-mediated endocytosis, followed by fusion/fission with an endosome
4
Q
Entry of non-enveloped viruses
A
- passage of genome through a channel in the membrane
- rupture/lysis of endosomal membranes
5
Q
Fusion (Entry of enveloped viruses)
A
- can occur at 2 main locations
1. Fusion of envelope with cell membrane, followed by delivery of nucleocapsid into the cytosol
2. Fusion of envelope with membranes of early or late endosome after receptor mediated endocytosis
6
Q
Attachment (Virus Entry)
A
- variety of cell surface molecules can serve as specific virus attachment factors and/or receptors
- needs to interact with both attachment molecule and an entry molecule
- virus can attach and then move along the surface of the cell until it hits the right kind of receptor for entry
7
Q
attachment factors/adhesion receptors
A
- cell surface components involved in binding to cell but not uptake
- considered primary receptors
- increase the probability of binding to the entry receptor
ex. glycoproteins
8
Q
Entry receptors
A
- needed for viral internalization
- play an active role
ex. conformational changes, cell signalling, endocytosis - considered secondary or co-receptors
9
Q
What surface components of a virion do host cell receptors interact with?
A
- viral glycoproteins
- surface protrusions
- surface depressions
10
Q
Receptor and virus interactions facilitate entry via what mechanisms?
A
- exposing fusion proteins on the virus
- new binding sites are revealed on virus and receptors as a result of conformation changes
- initiating endocytosis (signalling cascades in cells)
11
Q
Receptor mediated endocytosis (virus entry)
A
- carries nucleocapsid into cytosolic vacuoles.vesicles and then enter the cytosol
- once inside the cytosol, vesicles can fuse with other membranes structures within the cell
- can occur at clathrin coated pits, caveolae or lipid rafts that trap the virus at the plasma membrane and cause invagination (causing virus to go in)
- virus then delivered to early endosomes that mature into late endosomes
- they then enter the cytoplasm through fusion, lysis, or permealization
diff types: - clathrin mediated endocytosis
- caveolin-mediated endocytosis
- non-clathrin, non-caveolin endocytosis
12
Q
Macropinocytosis (virus entry)
A
- normal process in the cell that is exploited by the viruses
- the virus attaches and activates intracellular signalling
- it causes actin remodelling that causes a protrusion in the plasma membrane
- as the remodelling of actin continues, it forms a vesicle
- internalization forms large vacuoles called macropinosomes that mature and then fuse with the endosome
13
Q
Acidification (virus entry)
A
- passage from endosomes to the cytosol is often triggered by a low pH
- low pH signals to the virus it has reached intracellular compartments
- this induces conformation changes in viruses, can trigger different signalling mechanisms or various processes like lysis
14
Q
The self-replication RNAs to DNA step in evolutionary origin likely involved
A
- RNA-dependent RNA polymerases (RNA replication)
- RNA-dependent DNA polymerases (reverse transcriptases) (RNA to DNA)
- DNA-dependent RNA polymerases (DNA to mRNA)
- DNA-dependent DNA polymerases (DNA replication)
15
Q
Transition to DNA-based world
A
- started with self-replicating RNA molecules
- lead to production of deoxyribonucleotides from ribonucleotides
- made DNA copies of RNA (reverse transcriptase)
- advantage is that DNA is much more stable than RNA
