Biodiveristy: Viruses Flashcards
(21 cards)
What are the 3 hypothesis for the origin of viruses, explain
The Virus-First Hypothesis: pieces of RNA existed before the first cells. They slowly became more complex and gained the ability to self replicate by infecting other cells becoming viruses
Reduction Hypothesis: A large and small single celled organism form a mutualistic relationship. The smaller organism loses its protein building structures. It is now able to replicate itself and infect new organisms
Escape Hypothesis: unequal cell division results in the creation of 2 mini cells. The cell with a protein coat survives while the one without does not. This cell is now a virus.
Are viruses living? Why?
No they are not living.
- not made up of cells
- only capable of 1 life function (reproduction and only within a living cell)
- outside cells, viruses are lifeless chemicals
What is Viral size
20-400 nm
Explain the typical viral structure
Made up of a…
capsid: protein coat for protection, gives the virus it’s shape
Core: Either DNA or RNA (genetic material)
Receptor sites: spikes that help the virus attach to the host cell
Viruses are generally classified by?
The organisms the affect, structure (size and shape)
Explain Viral reproduction:
Lysogenic cycle (unfavourable conditions):
-phage DNA inserted into bacteria
-phage DNA integrates into the bacterial chromosomes becoming a prophage
-the bacteria reproduces normally, copying the prophage and transmitting it to the daughter cells
Lytic cycle (favorable conditions):
- phage DNA inserted into bacteria
- it uses the hosts metabolism to create new viruses
- the host cell dies and the new viruses are released
What are the disease patterns, explain
Endemic: a disease present in low levels (a sudden increase is called an outbreak)
Epidemic: occurs when an infectious disease spreads rapidly through a population and affect large numbers of people
Pandemic: when an epidemic disease spreads to other countries across the world
How do viruses make us sick?
-Cause disease by invading, destroying or disturbing the activities of the host cell
-trigger immune response
-interact with the hosts chromosomes creating cancer
-destroy the cell mediated response of the immune system
How do viruses move from one person to another
Sneezing - airborne
Touching - contact
Insects - vector
Exchange of bodily fluids
What is reassortment?
Viruses can mutate by capturing pieces of other viruses
Explain Natural Immunity
Immune response: specialized antigen resenting cells (APCs) engulf the virus and display portions of it to activate T-helper cells which enable other immune responses. B cells make antibodies which prevent the virus from infecting other cells and mark the virus for destruction. Cytotoxic T cells destroy the virus infected cells.
There is only one type of vaccine, true or false. Give an example
False there are many. An example is protein based vaccines which contain harmless pieces of the viruses protein which is selected to activate the immune response.
Explain Herd Immunity
The vaccination of a significant portion of the population provides a level of protection for those who have not developed immunity. R0 number: the higher the number the larger the portion of population must have immunity to stop transmission. How many people on average an infected person spreads the virus to. Herd Immunity Threshold: sufficient percent of the population which needs to have immunity to bring the spreading average to below zero.
Explain STIs and AIDS
STIs are sexually transmitted infections. AIDS is caused by a virus called HIV. It is one of the few which used RNA instead of DNA. Your body will try to fight the infection by producing antibodies. It is transmitted through blood, vaginal fluids, semen and breast milk.
Explain killing cancer with viruses
Specially modified viruses which can only replicate within tumour cells. It releases a protein which also increases the immune response to tumour debris
What is endogenous retrovirus
Endogenous retrovirus are the around 8% of our DNA sequence with viral origin.
When do we see the symptoms of a disease?
When a cell is destroyed by the virus
Why are viral diseases difficult to treat?
No drug is available to kill viruses within the body
Some viruses are lysogenic (hide inside cells for a long time (dormant)
Some are oncoviruses (cause cancer)
Explain Influenza A
- Common Flue
- spreads by direct contact
- attacks human respiratory tissue
- can live for hours in dry mucus
- destroys ciliated cells in the upper respiratory passage making it unable to sweep mucus and foreign particles out of the body
- symptoms include pain, fatigue and pneumonia
Explain how to protect yourself from viral diseases
- Vaccines: given dead or weakened form of the virus which allows the body to develop necessary antibodies
- Antiviral agents: given after infection to slow the reproduction of the virus
Explain viral uses for medicine
Viral vectors: modified viruses used to deliver genetic material to cells
Oncolytic virus for cancer therapy: insert virus which can only replicate in tumour cells. Also stimulates immune response to kill cancer cells
