Lecture 2 Flashcards
Components of a virus
Genome (DNA or RNA) & Protein
Functions of viral genomes
- Specify proteins
- Serve as a template for synthesis of progeny genomes
3 kinds of genome configurations & size
-Linear, entire genome on 1 strand
-Linear, segmented genome
-Circular genome
Types of genome modification
Four total
-Cap
-Poly A tail
-Viral proteins
-Cellular proteins
Role of secondary & tertiary structures in viral genomes
Four total
-Replication
-mRNA Synthesis: Recognition points for binding of viral or host proteins
-Packaging of the genome: Serves as signal to allow the genome but not other DNA/RNA to be put into viral particle
-Triggering the host innate antiviral response
Functions of genome modifications
4 main functions
-Aid in translation
-Stability of genome
-Packaging of genome
-Protect from host detection
How viruses deal with limited size
7
-Hijack host proteins for some or all replication functions
-More than one protein/gene
-Overlapping genes
-Genes on both strands of DNA
-Multiple splicing of same transcript to make numerous proteins with only one promoter
-Frameshift mechanisms allow downstream out of frame genes to be made at appropriate proportions
-Polyprotein production from one mRNA and subsequent proteolytic cleavage
Limits of genome size
4
-Replication rate: Especially in bacteria where virus must keep up with host since a large genome takes too long to replicate
-Size of virus particle: Larger the genome the larger the particle host must be
-Stability of genome
-Mutation rate of polymerase: Too many=loss of genome integrity, Not enough=Failure to adapt
Morphological unit
Surface structure seen by electron microscope
Capsid
Protein shell of a virus
Between ______% of viral particle mass is from protein
50-90%
Capsomere
A discrete component of a capsid, constructed from several identical protein molecules
Nucleocapsid
Viral nucleic acid enclosed in a protein capsid
Functions of virion proteins
3
-Protection of the genome
-Delivery of the genome
-Other interactions with the host
Envelope
Lipid bilayer containing viral glycoprotein
Assembly/Disassembly Paradox
Virus must be stable and protective enough to enter a host but fragile enough to disassemble within the host
How lipid bilayer is acquired from most cells
-Most acquired from hosts plasma membrane
-Others bud from internal membranes such as endoplasmic reticulum
Capsid function
-Protect genome from the atmosphere
-Delivery of genome in infectious form
Viral enzymes for which there are no host counterparts
In RNA, Vaccinia, and HIV
-RNA viruses: RNA-dependent RNA polymerase
-Vaccinia: DNA Dependent RNA Polymerase
HIV: Reverse transcriptase, Integrase, VPR (Helps evade host innate antiviral response
3 properties of helical viruses
- Positive charge interacts with nucleic acid
- Hydrophobic with proteins on either side
- Negative charge with polar environments
Cellular components of retroviruses
2
- Host cell tRNAs that function as primers for reverse transcription
- HIV: Cyclophilin A plays a role in infectivity
Hepatitis C virus
Associated with host lipoproteins
Hepatitis A virus
Physical Characteristic
Does not have an envelope when found in the environment, but acquires one from the cells that it grows in within the liver
Why study virion structure
3
-Attachment of host receptors
-Process of viral entry
-Process of viral assembly & disassembly
Function of virion proteins in protection of the genome
3
-Specific recognition and packaging of the viral genome
-Assembly of a stable, protective protein shell
-Interaction with host cell membranes to form the envelope
Function of virion proteins in delivery of genome
5 total: Emphasis on Delivery
-Specific binding to cellular receptors
-Induction of fusion of the viral envelope with cellular membranes
-Transmission of fusion of the viral envelope with cellular membranes
-Transmission of signals required for uncoating
-Interaction with cellular components to direct translocation of the viral genome to the appropriate sitw
Function of the virion proteins in other interactions with the host
3
-Ensures efficient infectious cycle
-Transport of viral components to assembly sites
-Host immune system interaction
