Ch. 18.2 Viruses & Prions
How many cold viruses would it take to span a period at the end of a sentence?
10,000 b/c viruses are some of the smallest disease-causing structures known
What must a virus do in order to replicate?
A virus must enter a host cell
Example of a retrovirus
HIV
What is evidence to support the most likely theory for the origin of viruses?
Scientists have found that the genetic material of viruses is similar to cellular genes. These genes somehow developed the ability to exist outside of the cell.
What is the most likely theory for the origin of viruses?
That viruses came from parts of cells
What is the next step after the virus attaches to the host cell?
The genetic material of the virus enters the cytoplasm of the host.
How is the brain affected when infected by prions?
These prions infect nerve cells in the brain, causing them to burst. This results in spaces in the brain, hence the description of spongiform (spongelike) encephalopathy (brain disease).
How do mutated prions affect normal prions?
They cause normal proteins to mutate.
Why are viruses not considered living things?
They do not exhibit all of the characteristics of live such as: - Have no organelles to take in nutrients or use energy - Can't make protein - Can't move - Cant replicate on their own
What does a virus use to attach to the plasma membrane of the host and how does this explain why man viruses cannot be transmitted b/w different species?
They use specific receptors on the plasma membrane of the host. Different types of organisms have receptors for different types of viruses, which explains why many viruses can't be transmitted b/w different species.
virus
a nonliving strand of genetic material within a protein coat
prion
a protein that can cause infection or disease, called a proteinaceous infectious particle
bacteriophage
a virus that infects bacteria
What do viruses that replicate by the lytic cycle produce?
active infections
What are the 2 parts viruses consist of?
capsid & genetic material
Examples of lytic viruses
common cold and influenza
retrovirus
contains RNA instead of DNA
Examples of lysogenic infections
herpes simplex I
genetic material
inside the capsid, DNA or RNA but never both
What do viruses that replicate by the lysogenic cycle cause?
latent infections
Examples of diseases caused by prions
mad cow disease in cattle, CJD in humans, scrapie in sheep, and chronic wasting disease in deer & elk
capsid
made of proteins
Normal prion structure
shaped like a coil
Mutated prion structure
shaped like a piece of paper folded many times
reverse transcriptase
used by retroviruses to transcribe DNA from the viral RNA
active infections
usually are immediate, meaning that symptoms of the illness caused by the virus start to appear 1-4 days after exposure
latent infections
when the viral DNA enters the nucleus it is inactive
