Viruses Flashcards
What is Koch’s postulates (To prove an agent causes a disease) (4)
Find Lesions
Isolate in pure culture
Inoculate pure culture to living organisms and cause disease
Recover again from lesion of host
What is the indirect demonstration of viruses (5)
Grind animal/plant infected tissue into fluid suspension Filter to retain bacteria Inoculate filtrate Watch for disease Repeat the whole process to confirm
What is a pock
Damage due to smallpox virus
What are 3 uses of tissue culture to grow virus
Develop Vaccines
Identify new viruses
Virus Diagnosis
What type of symmetry are present in “spherical” caspids
Icosahedral
What are the main compositions of Infectious particle or virion (6)
Genetic Material - DNA/RNA Protein Coat - Capsid Capsid and nucleic acid - nucleocapsid Non-structural proteins - enzymes Some viruses have an envelope - lipid bilayer and embedded glycoproteins Virus symmetry based on capsomeres
What are Satellites (2)
Contin Nucleic Acid but lack genes for replication
Depend on coinfection with helper virus
What are Prions
No nucleic acid
Infectious proteins
Disease
What are the properties of Viruses (7)
Infect animals, plants, bacteria
Size - too small for light microscope
Classified by morphology, genome and replication
Extracellular infectious phase
Obligatory Intracellular regulation
Viral Genes subvert cell biosynthesis to replicate
What is the overview of the infectious cycle (6)
Attachment and entry of the virion Decoding of genome information Translation of viral mRNA by host ribosomes Genome replication Viral Assembly Release of particles containing genome
What is the name of the viral attachment protein of influenza virus
Haemagglutinin
What is the viral receptor of influenza virus on the red cell
Sialic Acid
What is the name of the poliovirus receptor
PvR
What are 3 methods of viral entry
Fusion
Endocytosis and Fusion
Endocyosis
What does the viral genome contain
Information for instituting and completing an infectious cycle within a cell
What does expression and replication of the viral genome always depend on (2)
Depends on viral DNA or RNA
ALWAYS depends on viral mRNA
Which genes are transcribed pre replication
Early Viral Genes
What do Early Viral Genes do (3)
Regulate cell NA and protein synthesis
Regulate expression of the viral genome
Code for viral enzymes required for replication of viral nucleic acid
When are late viral genes transcribed
post-replication
What are the general features of the virus replication cycle (10)
Attachment Penetration Uncoating Transcription of Early mRNA Translation of early proteins Replication of viral DNA Transcription of late mRNA Translation of late proteins Assembly virions Release
What are the 2 types of Viral RNA polarity
Positive - acts as mRNA
Negative - complementary to mRNA, when copied (by RNA dependent RNA polymerase) acts as mRNA
What is the Baltimore classification
All viral genomes lead to mRNA
What are the 7 types of Nucleic acid used by viruses in Baltimore classification
dsDNA ssDNA dsRNA ssRNA (+) ssRNA (-) ss retrovirus RNA (+) Partially ds hepadnavirus DNA
How does HIV enter the cell
gp120 (on HIV) binds to CD4 on the cell surface of the Th Cell
Co-receptor on the surface of the Th cell attracts gp120 by chemotaxis
gp41 (on HIV) inserts a fusion peptide into the target bilayer
A 6-helix bundle brings the two membranes closer, allowing the membranes to fuse
What are the enzymes involved in the HIV replication cycle
Reverse Transcriptase
Integrase
Protease
What is pro-viral DNA (2)
Retroviral DNA integrated into the host cell genome = provirus
Template for retroviral mRNA and genomic RNA
Why do point mutations occur in RNA viruses
RNA polymerases have no proofreading
e.g. reverse transcriptase has no proofreading
What is a quasi species
a mixture of molecular variants of an RNA virus
