Week 5 Flashcards
Describe the relative size of viruses to other miroorganisms
Smallest
What is meant by viruses being infectious, obligate, intracellular parasites?
They cannot complete their life cycle without exploiting a host cell.
What do viruses require a host cell for?
To carry out genome replication and synthesis of viral compartments.
By what means are viruses within host cells transmitted to the next host cell?
Progeny virions
What are progeny visions?
They bud from one cell and allow spread of infection from one cell to another (used by viruses).
What do host cells provide to viruses and what is each component used for?
Nucleotides for nucleic acid production.
Ribosomes and amino acids for translation of proteins.
ATP for energy
Gold and endoplasmic reticulum for protein processing
What type of nucleic acids can viruses have?
DNA or RNA
What are the possible capsid structures of viruses?
Helical
Icosahedral
Complex
What are viruses without the presence of an envelope known as?
Naked
Describe the structure of a viral nucleocapsid .
Viral nucleocapsids are highly symmetrical and are composed of one protein capsid which is formed by the specific arrangement of capsomers.
How is the capsid of a virus formed?
By the specific self-assembly of capsomers.
Do viruses metabolise?
No
Do viruses respond to the environment?
No
What type of host cells do bacteriophage viruses infections?
Bacterial cells
Describe the virulence of bacteriophage infections
Highly virulent
What is the virulence of an organism?
The severity of harmfulness and ability of an organism to cause disease.
Is the structure of bacteriophages simple or complex?
Complex
Outline the features which are present in the structure of a bacteriophage.
Head, collar tail, tail pins, tail fibres
How are different bacteriophages classified?
By their shape and nucleic acids
What are the stages of bacteriophage life cycle?
Attachment
Penetration
Synthesis of nucleic acids and proteins
Assembly and Packaging
Release / lysis
Outline how bacteriophages undergo attachment to host cells.
All viruses have attachment proteins on their outside. This protein attaches to specific receptors on host cell surfaces. These viruses are normal proteins found on the outside of host cells
Where are the proteins that recognise host cells found in bacteriophages?
In the tail fibres
What do viral components mature to in the host cell?
Virons
What are Virons?
An entire virus particle consisting of a capsid and nucleic acid capsule.
What type of bacteria do T4 and Lambda infect?
E.Coli
Describe the virulence of T4 virus
Highly virulent
Describe the virulent of Lambda virus
Temperate
What is meant by a virus being temperate?
It does not immediately cause cell death
How many life cycles does the Lambda virus have?
2
What are the 2 life cycles of lambda?
Lytic and Lysogenic
What is the lytic life cycle of a virus ?
Infected bacteria are produced by Lambda bacteriophages and are lysed to release new bacteriophages
How do bacteriophages release new viruses in the lytic cycle?
By lysis of bacteriophage to release new bacteriophae
What is the lysogenic life cycle of a virus?
Bacteriophage genome is incorporated into bacterial host chromosome by genetic recombination that occurs at a specific site on the chromosome
By what process is a bacteriophage genome incorporated into a host cell genome in a lysogenic virus life cycle?
Genetic recombination
What is prophage?
The name for bacteriophage DNA when it is inserted into a bacteria host chromosome.
What is the name for bacteriophage DNA once it hast been inserted into a bacterial host chromosome?
Prophage
What type of cells does tobacco mosaic virus infect?
Plant cells
What type of structure does Tobacco mosaic virus have?
Helical symmetry and helical nucleocapsid
What type of viral nucleic acids does tobacco mosaic virus have?
RNA
Describe the most common shape of capsids in non-enveloped viruses.
Icosahedral
In non-enveloped, iscohedral capsids of viruses, how many capsid proteins are present?
Over 60
What are virus envelopes derived from?
Golgi membrane or nuclear membrane
How must viruses with envelopes be released fro a host cell?
They must or burst out of a host cell
Give examples of enveloped viruses
Measles
Influenza
Does influenza virus have an envelope?
Yes
How many main glycoprotein types does influenza virus have?
2
What are the 2 main types of Glycoproteins in influenza?
H- haemagglutin
N - neuraminidase
What is a retrovirus?
The DNA of the virus is converted to RNA by retrotranscriptase in the host cell.
What is used to classify influenza virus ?
The presence of different H and N proteins
What are the methods a virus can use to enter a host cell?
Direct penetration
Membrane fusin
Endocytosis
Outline the life cycle of an enveloped virus?
The envelope of the lipid bilayer of the virus has glycoprotein spices which fuse with the cell membrane of the hose cell.
The host cell is then used to synthesise a viral nucleic acid genome and viral proteins.
Endoplasmic reticulum of the host cell is used to make viral glycoproteins.
Progeny viruses bud from the cell and allow the cell membrane to kill the cell
Do enveloped viruses kill host cells?
No
What part of a host cell is used to make viral glycoproteins?
Endoplasmic reticulum
What are the possible sites of virus assembly with a host cell
Golgi, nuclear membrane, cell membrane
Describe the nucleic acid presence in HIV
Single stranded RNA
What type of virus is HIV?
Retrovirus
What are the possible effects of viruses on host cells?
Cytopathic effects
Transformation (tumour formation)
Lysis (cell death)
Persistent infection of cells
Latent infection of cells
What is meant if a virus becomes latent?
It lays dormant in host cell
What are the types of viral cellular culture?
Primary cell culture
Diploid cell lines
Continuous cell lines
What type of tissue are primary viral cell cultures obtained from?
Live animal tissue
Describe the life span of a primary viral cell culture
Very limited
From what cell type are diploid viral cell cultures obtained from?
Homogenous cells from embryos
Describe the life span of diploid viral cell cultures
They divide about 100 times and then die
Describe the life span of continuous cell lines
They are immortal and don’t stop growing
Where are continuous cell line cultures of viruses usually obtained from?
Cancerous cells
By what methods can viruses be quantified?
End point dilution assay
Plaque assay
What method is used to isolate a single virus?
Plaque assay
Outline the process of forming a plaque assay of a single virus
Virus innoculated on a monolayer of cells or bacteria.
Overlayer of agar added
(Virus can only spread cell to cell)
Holes or plates of dead cells form in the monolayer
Do plaques in a viral plaque assay show dead or live cells?
Dead
