Viruses & Prokaryotes Flashcards
Individual viral particle.
Viron
3 hypotheses of virus evolution:
Regressive Hypothesis
Progressive Hypothesis
Virus-First Hypothesis
Virus Evolution.
De-evolution Hypothesis
States that viruses were once free-living cells or intracellular parasites that decreased in complexity and eventually lost the ability to reproduce on their own.
Regressive Hypothesis
Virus Evolution.
Escapist Hypothesis
States that viruses arose simply from RNA or DNA, or from self-replicating mobile genetic material (like transports), that acquired the ability to leave their native host cell for another.
Progressive Hypothesis
Virus Evolution.
Suggest that viruses existed as the first self-replicating entities, predating cells.
Virus-First Hypothesis
The genome of single-stranded RNA (ssRNA) viruses can act not only to store genetic information but also as the mRNA used for protein translation.
Positive Sense —> (+)ssRNA
Have a genetic sequence complementary to their mRNA.
Negative Sense —> (-)ssRNA
4 types of viral capsids:
Helical Capsids
Icosahedral Capsids
Enveloped Viruses
Complex Viruses
Viral Capsid
Shaped like long cylinders.
Helical Capsids
Viral Capsid
Look like multifaceted 3D spheres but are formed from 20 equilateral triangles.
Icosahedral Capsids
Can have Icosahedral or helical capsid and posses a plasma membrane that’s derived from their host surrounding their capsid.
Enveloped Viruses
Can have Icosahedral or helical shapes with an outer shell wall or have the 2 shapes put together to form a head and tail.
Complex Viruses
Viruses that infect bacteria.
Bacteriophages
5 steps in the infection/replication cycles of a virus:
Attachment
Penetration
Uncoating (if necessary)
Replication
Assembly
Release
Step 1 in the infection/replication cycle of a virus:
A capsid protein or envelope glycoprotein of a vision binds to a receptor on the membrane of the host cell.
Attachment
Step 2 in the infection/replication cycle of a virus:
A virion enters the host cell through one of several methods - endocytosis, fusion, injection.
Penetration
Method of Penetration
The host cell membrane engulfs the virion.
Endocytosis
Method of Penetration
The viral envelope merges with the host cell membrane.
Fusion
Method of Penetration
The contents of the capsid are injected into the host cell.
Injection
Step in the infection/replication cycle of a virus if the viron entered the host cell:
The capsid is degraded, releasing its contents.
Uncoating
Step 3 in the infection/replication cycle of a virus:
DNA viruses - typically exploit the existing machinery of a host cell to replicate DNA, transcribe mRNA, and direct protein synthesis
RNA viruses - replicate in a similar manner but their genetic code may also function as mRNA
Replication
If a host cell not only allows a virus to attach, but also to use the cell to replicate, the cell is __________.
Permissive
Step 4 in the infection/replication cycle of a virus:
Once replicated, involves packaging the viral genome into newly assembled capsids.
Assembly
Step 5 (last step) in the infection/replication cycle of a virus:
Egress.
Newly assembled visions are released from the host cell via lysis or exocytosis.
Release
Cell bursts open killing the cell by rupturing the membrane.
Lysis