Disease and Defence Flashcards
Why are viruses classified as non-living?
They are acellular. No cytoplasm, no metabolism and can’t self-replicate
Name 3 types of virus and give examples
DNA virus - lambda phage
RNA virus - Ebola
RNA retrovirus - HIV
Describe Ebola
Caused by the Ebola virus. Spread by direct contact with infected body fluids. Symptoms include fever, vomiting, diarrhea and internal bleeding.
What virus causes Ebola?
Can be caused by different viruses, all members of the Ebolavirus genus which is part of the filoviridae (filament shaped) family of viruses.
Compare and contrast the tobacco mosaic virus and Ebola.
Both are RNA viruses. Tobacco mosaic virus contains ssRNA, which can be directly translated into proteins by ribosomes. Ebola contains negative ssRNA, which needs to be transcribed to produce mRNA before translation.
How does the tobacco mosaic virus cause disease?
It affects plants, mainly transmitted via infected sap. Contains ssRNA, which is directly transcribed by host cell to create new virions. Virions enter other cells via plasmodesmata. Causes stunted growth and mottled leaves.
What is tuberculosis?
A bacterial disease caused by Mycobacterium tuberculosis and M. bovis. It damages the lymph nodes in the lungs and neck, and weakens the immune system.
How is tuberculosis transmitted?
Airborne droplet transmission
What is the lambda phage virus?
A type of bacteriophage virus which infects E.coli bacteria.
Describe the general structure of a lambda phage virus.
It has a head and tail region. The head contains a double stranded DNA genome. The tail facilitates attachment and the insertion of viral DNA into the bacterium.
Describe the lysogenic pathway.
- non-virulent viruses inject DNA into host cell DNA as provirus. Viral DNA replicates when host cell divides.
- Virus produces repressor proteins to inhibit transcription
- Latent virus enters the lytic pathway when host cell is damaged or immune system weakens.
Describe the lytic cycle
- Virulent viruses inject nucleic acid into host cell cytoplasm. Viral genetic information replicates immediately, independently of host cell DNA.
- Many virions assemble, causing cell lysis
Describe HIV
Caused by human immunodeficiency virus,
Spread by direct contact with infected body fluids. Destroys white blood cells making the individual immunodeficient and increasingly susceptible to other diseases. Leads to AIDS.
How does HIV result in the symptoms of AIDS?
- Attachment proteins bind to complementary CD4
receptor on TH cells - HIV particles replicate inside TH cells, killing or damaging
them - AIDS develops when there are too few TH cells for the
immune system to function - Individuals cannot destroy other pathogens and suffer
from secondary diseases/ infections. May cause death
What is the latency period?
The period of time following infection before symptoms appear.
What is a pathogenic organism?
An organism that has the ability to cause damage to the host.
Give 4 major routes of infection in humans.
-Droplet infection (coughing/sneezing)
-Direct contact (skin to skin or bodily fluids)
-Oral (ingesting contaminated food/drink)
-Airborne (small infected particles travel in the air)
What is indirect transmission?
Transmission which requires a vector intermediate
Outline the natural defenses in the body that reduce the risk of infection
Skin, skin flora, blood clotting, lysosomes, hydrochloric acid, mucus membranes, phagocytosis, inflammation
What are skin flora?
Microorganisms which naturally live on the skin. They are usually harmless to humans but act as a useful defense against pathogens.
How do skin flora help to prevent infection?
They compete with pathogenic microorganisms for resources and nutrients. This hinders growth of harmful microorganism colonies.
What are non-specific immune responses?
Defenses which don’t target a single type of antigen or pathogen, but a wide range of different pathogens. Examples include inflammation and phagocytosis.
Name 4 ways the nonspecific immune system responds to infection.
-inflammation
-phagocytosis
-digestive action of lysosomes
-production of interferon (antiviral agent)