BIO CHP 19 3
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. What would you like to do?
Who was a Russion biologist and what did he do?
Ivanovski; identified the cause of tobacco mosaic disease as juice extracted from infected plants
How old was Ivanovski when he discovered this?
Who was a Dutch scientist and what did he do?
Beijerinck; Suggested that tiny particles in the juice caused the disease and he name them viruses
In what process do viruses multiply immeadiately after infecting the cell?
What one thing do all viruses have in common?
They enter living cells and, once insiede, use the DNA of the infected cell to produce more viruses
What happens first once a virus injects its genetic material into a cell?
The viral genes are expressed
What does the cell do to the viral DNA or RNA after the genes are expressed?
Transcribes and translates the viral genetic infromation into viral capsid proteins
What does the viral genetic program sometimes do?
Cause the host cell to make copies of the virus and in the process the host cell is destroyed
Why are most viruses highly specific?
Because they must bind precisely to proteins on the cell's surface and then use the host's genetic system
Explain what happens after bacteriophage T4 infects a cell in a Lytic infection.
- Has a DNA core inside an intricate protein capsid that is activated by contact with a host cell
- Injects its DNA directly into the cell
- The host cell cannot tell difference between its DNA and virus' DNA so the cell begins to make mRNA from the genes of the virus
- The viral mRNA is translated into viral proteins that chop up the cell DNA and shut down the infected host cell
- The virus then uses materials of the host cell to make thousands of copies of its own DNA molecule
- The viral DNA gets assembled into new virus particles
- The cell lyses before long
What type of infection where viruses prophages will be present many years before becoming active?
What happens in a lysogenic infection?
A virus combines its DNA or RNA into the DNA of the host cell and the viral genetic information replicates along with the host cell's DNA
What is a prophage?
The viral DNA that is embedded in the host's DNA and is not active
What will happen when a prophage becomes active?
It will remove itself from the host cell DNA and direct the synthesis of new virus particles
What are retroviruses?
Viruses that contain RNA as their genetic information
How did retroviruses get their name?
"Retro" means backward and a retroviruses' genetic information is copied backward so instead of DNA->RNA it copies RNA->DNA
What is a VERY common disease retroviruses are responsible for some types of?
What do retro viruses take advantage of in the host cell?
- All other functions that occur in living things
What are viruses considered as and why?
Parasites because like parasites, viruses depend upon other living organisms for their existence and harm that organism in the process
Are viruses alive?
No, but they have many characteristics of living cells
Why are viruses not considered to be living?
Because they aren't made of cells or able to live independently
What can viruses do after infecting a cell?
- Regulate gene expression
Why couldn't viruses have been the first living things?
Becauses they live off of other living organisms so they had to evolve after living organisms did
How may have the first viruses evolved?
From the genetic material of other living cells
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