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Transcript of Viruses
Can be classified into orders, families, genera and species
160 major groups of viruses, with 3000 viruses classified into these groups
However, there are millions of unclassified viruses that virologists are still trying to classify
Viruses are classified in a variety of different ways. Some include:
How are viruses classified?
Viruses and their Shapes
Viruses that infect humans are classified into 21 groups
Joyce Costa, Cassidy Da Silva & Siobhan Keane
All Viruses Contain:
contains the genome of the virus
Nucleic Acid Core
Makes up 95% of the virus
Helps the virus attach to the host cell and protects the virus from being attacked by the host cell’s enzymes
Capsids are usually either helical or icosahedral and are always symmetrical
Some mutations have caused spikes or other oddities on the capsid of viruses
The shape of the virus is determined by the arrangement of the proteins in the capsid
Viruses have a multitude of genetic uses
useful for genetic engineers
they enter the host cell and take over the functions of the DNA in the host cell
copying a gene > they insert the genetic material into a virus
each new virus cell contains the gene that the researchers wanted copied.
Other Uses Include....
Envelope comes from cells that it has infected
Entering the Body
What is a Virus?
- a structure that contains strands of DNA or RNA surrounded by a protective protein coat. It cannot live independently outside of cells
Viruses were discovered in 1935 by Wendell Stanley.
They are much smaller than bacteria and are very simple as compared to living organisms.
Some scientists believe viruses living organisms, while others do .
- a single individual particle of a virus
size and shape
method of replication
whether they contain DNA or RNA
what group of organisms they infect
types of diseases they cause
whether they are enveloped or not
Most common shapes: helical, polyhedral, complex and enveloped
Due to mutation and adaptation, viruses have evolved and formed new shapes
Shape is one of the most common characteristics used to classify viruses.
Are a combination of helical and icosahedral characteristics
The nucleic acid core is wound tightly inside a capsid shaped like a cylindrical tube
The cylinder may be flexible or rigid
Icosahedral or helical capsid that is encased by a lipid bi-layer membrane
May have an outer wall structure like the variola virus
May have a head and tail morphology like the bacteriophage
The capsid contains the genetic information in a spherical- looking shape
The capsomeres are joint together to form a many sided shape that resembles a sphere (icosahedral)
Replication of a virus ending with the death of the host cell
the replication process in viruses in which the viral DNA enters the host cell's chromosome
2 Reproductive Components
breaks down the pre-existing DNA
Synthesis of viral genomes and proteins
New viruses are released
Normally when conditions are favorable
May lay dormant before instructing the production of new viruses
certain factors determine whether
lytic cycle is induced
lysogenic cycle begins
daughter cell with prophage
Many cell divisions lead to a large population of infected cells
Phage DNA integrates into the host chromosome
Cell replicates - phage is copied to the 2 daughter cells
What does this prove?
why viruses do what they do
Cold sores/fluid filled blisters on the lips, tongue or genitalia
Human Immunodeficiency Virus
Fever (common symptom)
Muscle and joint aches and pains
BOTH USE THE SAME REPRODUCTIVE PROCESSES
BUT THEIR TIMING AND USE IS WHAT SEPARATES THEM
Cold sores = Destroyed Cells
when in provirus stage
Infects cells with provirus, but also continues the production of new viruses
(two different teams)
A virus is not a live cell, it must have a host cell to live and replicate.
Viruses are dormant outside cells
If an area has been contaminated with a virus, until that area has been properly disinfected, for some time after, organisms can still be infected
Can enter an organism through the nose mouth or breaks in the skin
Travels through the organism to find specific host cells to attack
Ex. Cold and flu viruses attack respiratory and digestive tracts
HIV/AIDS attacks the T-cells of the immune system
immune system > pyrogens > fever
slowing down the rate of viral reproduction
with a higher temperature, reactions slow down
antibiotics cannot treat viruses
By understanding how they function, the same processes can be used for other purposes
genetic engineering > carriers
new chemical possibilities
The Tobacco Mosaic Virus
destroys crops like tobacco, tomatoes, peppers and other vegetation
scientists are harnessing its characteristics to build parts for lithium ion batteries
They do not have any organelles, cytoplasm or cell membranes
Therefore, they are not cellular
Viruses are measured in nanometers
Nucleic Acid Core
contains either RNA or DNA
may contain one or multiple nucleic acid segments
- the protein layer that surrounds the genetic information of virus
- a single subunit of a capsid
These structures are only found in some viruses
What are the main differences between the lytic and lysogenic cycle? Compare their main functions and processes.
2 reproductive processes
proteins on the surface of lipid envelope, allowing the virus to interact with its host cell
a fatty acid covering that surrounds the capsid
area between the capsid and the envelope that contains viral proteins
Checking For Understanding
A virus has many components. Which is not one of them?
a) A nucleic acid core
b) A protein layer that surrounds the nucleic acid core
c) A fatty acid layer that surrounds the protein layer (mentioned in b)
d) Proteins that sit on a fatty acid layer (mentioned in c)
e) A layer that surrounds the proteins found on the fatty acid layer (mentioned in c)
Answer: e). No membrane surrounds the envelope proteins found on the lipid envelope.
Checking for Understanding
There are many shapes of viruses, four being the most common. They include all but:
Answer: d). Tetrahedral is not a virus shape. Polyhedral, icosahedral, complex and helical are the most common virus shapes.
a) A proton is to a neutron
b) A tree frog is to a bullfrog
c) A limb is to an organism
d) All of the above
e) a & b
Answer: C because a limb is a single component of an organism just like a virion is a single component of a virus
Checking for Understanding
A virion is to a virus as...
a) bodily cells
c) plant cells
d) individual organs
Answer: D because viruses do not attack tissues or bodily systems as a whole, they are solely capable of entering the system through a cell
Checking for Understanding
Viruses attack all of the following except: