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
When budding occurs on the cell membrane allowing individual virions to exit without much damage.
Common with many viruses that affect animals.
Exocytosis
Programmed cell death.
Apoptosis
A lag between when the virus infects the host and when it replicates and affects the host.
Latency
2 main cycles of virus reproduction:
Lyric Cycle
Lysogenic Cycle
Virus Reproduction
Viruses quickly reproduce inside the host cell until it bursts open, releasing many new viruses.
-most common
Lytic Cycle
Virus Reproduction
Viral DNA becomes a part of the host’s genome and can persist for a long time before environmental triggers cause the virus to switch to the lytic cycle.
-slower
-only seen in viruses that infect bacteria
Lysogenic Cycle
Virus Reproduction
Follows the steps of attachment, penetration, Uncoating, replication, and assembly BEFORE finally ending with the production of so many virions that the host cell lyses (bursts) and releases them all.
Lytic Cycle
Virus Reproduction
Slower process through which viral DNA becomes integrated into the host genome.
Only seen in bacteria and the viruses that infect them (bacteriophages).
-In this cycle, DNA from the bacteriophage enters the host cells and becomes part of the host’s genome, where it can persist indefinitely.
Lysogenic Cycle
Virus that infects bacteria.
Bacteriophage
Replication of bacteriophages.
Lysogeny
Environmental triggers eventually cause a virus to shift from the lysogenic cycle to the lytic cycles.
The prophase DNA is removed from the host DNA and the virus enters the lytic cycle.
Induction
Koch’s Postulates:
- The microorganism can be found in high abundance in symptomatic individuals.
- The microorganism can be isolated from a symptomatic individual and grown in a laboratory culture.
- Inoculating a healthy individual with the cultured microorganism produces the disease.
- The microorganism in the inoculated, diseased individual can be retrieved and identified as the same microorganism from the original diseased host.
Disease-causing microbes (infection) transmitted from a parent to offspring.
Vertical Transmission
Disease-causing microbes (infection) transmitted from one individual to another.
Infection from one person to another (usually due to contact with bodily fluids).
Horizontal Transmission
Symptoms develop and resolve within a relatively short period of time.
Acute Disease
Symptoms last for longer periods of time or event indefinitely.
Chronic Disease
When a disease occurs suddenly and in high numbers within an area.
Outbreak
Ensues when a disease outbreak spreads to a greater number of people over a larger area.
Endemic
Is declared if the original outbreak rapidly spreads to afflict multiple countries, continents, or the entire globe.
Pandemic
Viruses that have the capacity to cause cancer.
Oncogenic Viruses
Weakened viruses.
Attenuated Viruses
A single viral protein.
Prion
A circular strand of RNA.
Viroid
Proteinaceous infectious particles that contain no genetic code.
Extremely hardy and don’t break down in the intestinal tract.
Irregular variant of a normal protein produced by the host.
Replicate by entering a cell, binding to the normal version of the protein, and converting that protein into the infectious variant, forming a new prion. —> Go on to alter more normal proteins (so prion replication increases exponentially.
-ex. Spongiform encephalopathy —> “mad cow disease”
Prions
Small, circular ssRNA particles that aren’t housed in a capsid nor do they produce any proteins.
Their sole function is to reproduce RNA sequence using the host cellular machinery
Viroids
Additional layer surrounding the cell wall of bacteria that serves as camouflage from a host’s immune system and to aid in attachment to surfaces.
Gelatinous Capsule
How genetic material is shared in prokaryotes:
Transformation
Transduction
Conjugation
Fragments of DNA are taken in from the environment and incorporated into the genome.
Transformation
Genetic material is transferred from one cell to another by a bacteriophage (from one bacterial cell to another).
Transduction
A donor cell extends a long, hollow pious to a recipient cell, forming a conjugation bridge.
Conjugation
Fragment of DNA are taken in from the environment and incorporated into the genome.
Transformation
Genetic material is transferred from one cell to another by a bacteriophage.
Transduction
Involves the duplication and transfer of a plasmid from a donor cell to a recipient cell via pious bridge.
Conjugation
Primary mode of reproduction for prokaryotes.
Results in the formation of 2 identical daughter cells.
Genetic material in the nucleotide region is duplicated and separated. —> As the DNA is replicated, the cell enlarges and begins to produce material for a new cell wall, creating a septum through the equatorial region of the cell, the cell pinches inward to form 2 separate cells.
DOES NOT allow for the recombination/exchange of genetic material.
Binary Fission
A symbiosis in which one species benefits and the other is unharmed.
Commensalism
Pathogenic prokaryotes are considered parasites. —> Harming their hosts by infecting them.
Parasitism
Bacteria are used to degrade/remove pollutants from the air, water, and soil by processing materials like raw sewage, petroleum/crude oil spills, and industrial waste.
Bioremediation
Thin films of bacteria that stick to surfaces.
Biofilms
