Lesson 3: Viruses

Question 1

Viruses

Answer 1

Non-cellular particle made up of genetic material and protein that can invade living cells

Question 2

viral structure

Answer 2

-all viruses consist of a core of DNA/RNA surrounded by protective protein coat called capsid.
-some viruses have an envelope that contains protein spikes (antigens) that are used to infect living cells

Question 3

Viral specificity

Answer 3

virus tend to infect only one type of host such as: human, potato plants

there are some that infect a more general group of organism such as mammals

Question 4

Viral specificity examples

Answer 4

Rabies, influenza

Question 5

Viral life cycles

Answer 5

to reproduce, viruses must invade or infect a living host cells
—> two general life cycles of a virus:
1-lytic cell, 2-lysogenic cycle

viral doesn’t want to kill you, they want to survive and reproduce

Question 6

lytic cycle

Answer 6

1. Special molecules on the viral tail fibers match the cell membrane proteins in the host cell
2. Attachment of the virus and injection of its nucleic acid then takes place
3. Usually the host cell cannot distinguish between host and viral DNA, and will transcribe both
4. The viral mRNA acts like a molecular wrecking crew, shutting down and taking over the host cell
5. Host DNA is destroyed but not the viral DNA
6. The viral DNA uses the cells resources to construct hundreds of virus particles
7. This whole process may take as little as 20 minutes
8. Lytic infection follows when the cell bursts and releases active viruses to infect other host cells

Question 7

Lysogenic cycle

Answer 7

1. after infection, the viral DNA inserts itself into the hosts DNA
2. This combo is now called a prophage
3. This may remain part of the host DNA for many generations

Question 8

Lysogenic cycle- prophage may:

Answer 8

-block entry of other viruses to the host cell
-may insert useful DNA
-prophage DNA may become active, remove itself from the host DNA and start to produce virus particles. The trigger for this change may be sudden temp. or nutrient changed

Question 9

Rectroviruses

Answer 9

-a special class of viruses that contain RNA as their genetic material
-also contain the enzyme Reverse Transcriptase that allows the virus to “reverse transcribe” viral RNA into DNA that is then inserted into the host genome

Question 10

The debate: are viruses alive?

Answer 10

since all viruses depend so completely for their existence on living cells, it is unlikely that they evolved first.
it is more like that they developed from genetic material of living cells and have continued to evolve ever since.

viruses are considered parasites (depend on another organism to sustain them and harm their host in the process) viruses are not considered living cells however they are clearly part of the system of life on Earth