L14 - Virus Lifecycle: Entry & Exit Flashcards
In simple word, describe the virus lifecycle
- bound by intercting with cellular proteins
- nucleic acid released into cytoplasm
- stays in cytiplasm to replicate (RNA), DNA virus stays in nucleus (rough rule)
- replicates genome and produces genome which makes virus structure
- virus assembly depending on where teh viorus is replicating
- it is released to infect new cells
What are the 7 steps to viral replication life cycle
- Adsorption (attachment)
- Entry
- Uncoating
- Genome replication & translation
- Synthesis of virus components
- Assembly
- Release
How does virus adhere to gain entry
They use components of the cell membrane as receptors
- need to bind to gain entry
- usually glycoproteins or carbohydrate residues
Explain the adsorption attachment stage
- random collision
- interactions between proteins (capsid interacts with receptor proteins if no envelope, if has envelope then its their glycoproteins interacting)
- tropism for specific cell bc they express a specific thing
Fill in gaps: adsorption
- some viruses may use ______ host cell receptor
- usually infect a ____ ____ of cell types (tropism)
- ______ ______ are specific for vision attachment proteins (blocks interaction with receptors)
- more than one
- limited spectrum
- neutralising antibodies
What type of receptor is needed to gain entry/fascilitate the fusion of the cells? Give examples
Co-receptors
CCR5 - macrophages
CXCR4 - T cells
What is the influenza virus receptor ?
Sialic acid
What prevents avian influenza strains from efficiently infecting and spreading among humans?
Natural Species Barrier: Limits cross-species infection.
• Receptor Specificity:
• Haemagglutinin binds to specific sialic acid structures.
• Avian influenza prefers one form; human influenza prefers another.
• Human Respiratory Tract (RT) has the human-preferred sialic acid type.
• Result:
• Avian strains infect birds efficiently.
• Poor adaptation to human RT makes human infection and transmission harder.
What are the 2 mechanisms of viral entry (penetration)
Endocytosis, fusion of virus envelope with CM
Describe the uncoating process of viral replication
- release of viral genome
- cell enzymes (lysosomes) strip off the virus protein coat
- vision can no longer be detected = eclipse period
What is the eclipse period
Virus structure is destroyed and vision can no longer be detected
What are the 3 locations at which uncoating can take place
Plasma membrane, within endosomes, at nuclear membrane
What is the tegament region
Region of protein between capsid and envelope that gets left outside
Outline the steps of HIV entry
- gp120 protein attaches to CD4 on target cell
- conformational change
- recruits CCR5
- gp41 membrane insertion
- membrane fusion ( hydrophobic ion acid wants to avoid aqueous environment)
Describe the influenza virus entry and decorating
- interacts w sialic acid and taken in through endozome
- low pH in endosome causes conformational change
- 2 membranes fuse and releases viral NA into cell (viral envelope and endosomal membrane)
SARS CoV attachment and entry
S glycoprotein (spike) interacts w primary receptor (TMPRSS2)
Makes protolytic cleavage an activates it
Non-enveloped viruses (poliovirus) entry and uncoating
After receptor attachment
- virus taken up into endosome
- conformational changes to viral structural proteins
- results in formation of a pore in the endosomal membrane
- viral DNA is released into cytoplasm
Adenovirus entry
- DNA virus (ataches through spikes on capsid)
- taken in as endosome
- acidified endosome leads to partial uncpoating of capsid
- endosome membrane ruptured and partially coated capside interacts with microtutbules which transports to nuclear pores where it disassembles completely and injects its DNA into nucleus to replicate
What is an example of a virus that has to travel a long distance
- herpes infects nerve cells
- gain entry in nerve cells and gets transported to nucleus (very far away)
- uses microtubules and energy dependednt process to end up at nucleus
- released and replicated, transported to terminal to exit
Where is virus assembly?
Cell nucleus, cytoplasm, plasma membrane
Non enveloped = assembles in cell
Enveloped = gradual extrusion
How are viruses released. Enveloped vs non-enveloped
Sudden rupture of cell (non enveloped virus), gradual extrusion (budding) of enveloped virus’s through the cell membrane (enveloped). May occur together with assembly
How does enveloped virus budding occur
Interacts w glycoproteins, gradual extrusion of virus budding out, membrane pinches off at surface releasing enveloped virus to cells
Influenza virus assembly
- ow many separate segments
- is it specific or random genome segment packaging
8, specific interactions
Explain HIV maturation
HIV maturation is driven by virion protease, only mature HIV is infectious
- virus released in immature form (protease is within this)
- protease → protolytic cleavage of proteins → mature (rearrangment of structures within capsid)
- only mature HIV is infectious, good target for antiviral drugs (stops maturation to limit the ability of the virus to spread)
What is the use fo ER and golgi
- virus make use of other structures within the cell in order to assemble and release
- herpes & corona for example
- makes use of secretery pathway of teh cell to release particles outside
Herpesvirus assembly and release
- large DNA virus that replicate in nucleus and seembles capsid structures
- within capsid = DNA genome
- produces problem: structure it too big to exit through nucleus pores
- it goes through budding through inner membrane of nucleus where it gains encelope
- binds to receptor on the outer membrane and fuses w outer membrane (similar to entry process but its exiting using the fusion)
- bud in to golgi apparatus (acquring envelope)
- enveloped virus particle is secreted from cell
Coronavirus assembly and release
- virus replicates its genome
- assmbles with nuclear p[roteins and recognises spike oroteins
- interacts, buds into vesicle and gets released to the outside of cell
- assembly process starts in cytoplasm
Poliovirus assembly
- no enveloped virus
- capsid made of 4 virus proteins
- when they are produced they self-assmble into capsid structure
- interaction of protiens is lose, there is gaps which allows RNA genome entry to enter (pores through the structure)
- protlytic cleavage events (proteases) → allows rearrangemnet of capsid and seals up the capsid and prevents RNA from escaping
- RNA gains exit when infecting new cells
