Viruses and Viral Disease Flashcards
Lecture 15 - 22
Write 3 fun facts about viruses.
Viruses infect all living organisms.
We breath and eat billion of virus particles.
We carry viral genetic sequences as part of out own genetic materials.
Describe the history of viruses/virology.
Tobacco Mosaic Virus was identified in the 1930s.
Viral diseases like rabies have affected humans for many centuries.
The first written record of a virus infection is shown in hieroglyph from Memphis.
Pharaoh Ramses V (died 1196 BC) due to smallpox.
In the late 18th century, Edward Jenner observed a milkmaid who caught cowpox and was found to be immune to smallpox. In May (1796) Jenner used pus from that milkmaid to vaccinate the 8 year old boy. In July (1796) Jenner tried giving pus to the boy and he survived.
How did Dmitri Iwanowski (1892) help in the development of concepts of viruses.
He demonstrated that extracts from infected tobacco plants could transmit disease to other tobacco plants. He filtered the extract with the Chamberland filter (a porcelain filter developed to remove bacteria from drinking water). This didn’t prevent transmission.
How did Martinus Beijernick (1898) help in the development of the concept of viruses.
Showed that the filtrate contained a new form of infectious agents. He demonstrated that the agent multiplied in living cells. He called it a soluble living germ and used ‘filtrable agent’ to describe it.
How did Loeffler and Frosch (1898) aid in the discovery of the first animal and human viruses.
Repeated the TMV experiments and demonstrated Foot and Mouth Disease in cattle was caused by similarity small infectious agents.
How did Carlos Finlay (1901) discover the first human virus.
A Cuban physician, first conducted and published research that indicated that mosquitoes were carrying the cause of yellow fever. So the first human virus to be identified was the yellow fever virus.
5 properties of viruses.
- Small
- Contain DNA or RNA
- Different replication strategy, they don’t divide by binary fission.
- Obligate intracellular parasites
- Simple structure.
3 reasons why we study viruses
- To understand viral disease.
- Develop therapeutics
- Design measures to reduces viral transmission.
What is a virus definition?
Viruses are genetic elements surrounded with a capsid and can’t replicate independently of a living cell.
What isn’t encoded in viral genomes?
Genes that encode the complete protein synthesis machinery.
Genes encoding proteins involved in cell wall production or membrane biosynthesis.
Centromeres or telomeres found in standard host chromosomes.
Describe the CAPSID.
The protein shell that surrounds the viral genome.
It protects the nucleic acid.
Facilitates nucleic acid delivery into the host cells.
Composed of protein molecules arranged in a precise and highly repetitive pattern around the nucleic acid.
Viral genomes are small and encode a limited number of proteins.
Viral particle would be built with multiple copies of these few proteins.
What are the 3 types of CAPSID.
Helical, Icosahedral, Complex.
What is an Icosahedron in terms of its structure?
20 faces - each an equilateral triangle.
30 edges - each an interface between 2 faces.
12 vertices - each a point where 5 faces meet.
It permits the greatest number of capsomeres to be packed in a regular stable figure icosahedron. The easiest way of making regular stable structure from the smallest number of proteins. There is 2 fold, 3 fold and 5 fold symmetry.
Give an example of viruses with simple Icosahedral capsids.
Adeno-associated virus. Parvovirus B19. 25nm with 60 copies of a single viral capsid protein.
What is helical symmetry?
Rod - shaped viruses.
The length of virus determined by length of nucleic acid. Width of virus determined by size and packaging of protein subunits.
Describe how viral particles are metastable.
Protects viral genome (stable). Facilitates delivery of viral genome into the host cell, must dissociate on infection (unstable).
Describe how CAPSID proteins are related to Virus-Like Particles.
Some CAPSID proteins self-assemble into virus like particles.
Why are viruses classified?
To contrast viruses and to reveal information on newly discovered viruses by comparing them to similar viruses.
To study the origin of viruses and how they have evolved over time.
What is the disadvantages of classification based on diseases?
Focuses on some viruses and ignores the others.
A single virus may cause more than one disease.
Viruses infect more than one host and sometimes with different manifestations.
What are the disadvantages of classification based on host.
Some have restricted host range.
Others infect a small range of hosts.
Some infect very different species.
Some grouped based on the nature of the host cells.
What are the characteristics for the committee on taxonomy of viruses (ICTV).
Host range, morphological features of the virion, nature of the genome nucleic acid, additional features may allow subdivision allocation, phylogenetic trees may be established using nucleotide sequences.
What is the baltimore classification of viruses.
Thousands of different viruses.
Cause different numbers of viral infections and diseases.
All viruses must make their mRNA.
mRNA will be read by the host ribosome to produce the viral proteins.
No exceptions to this.
Describe viroids.
Novel agents of disease in plants. Contains a single circular ssRNA molecule as infectious materials. No protein components. Viroids genomes range in size from 220 to 400nt. The smallest self-replicating pathogens known. Up to 70% of the nucleotides in the genome RNAs are base-paired. They appear as rod-shaped or dumb-bell shaped molecules.
Describe prions.
Originally thought to be viruses as they replicate slowly within their hosts. No nucleic acid has been found in association with infectious material. Agents of a number of diseases characterized by slow, progressive, neurological degeneration that are fatal. The diseases are associated with a spongy appearance of the brain. It induces changes in the shape of their normal homologoues with catastrophic consequences.
