Biological Diversity: Viruses Flashcards
Viruses
Non living infectious particles capable of infecting other cells, replicating inside of them and continuing to infect more cells
Types of viruses
Bacteriophages
Retroviruses
Retroviruses
RNA viruses that use reverse transcriptase to create dsDNA transcripts from single stranded RNA genome
Virus components
Nucleic acid
Capsid
Viral envelope
Nucleic acid ( viral genome)
Double or single stranded RNA or DNA
Prophage
Viral genome integrated into bacterial genome
Provirus
Viral genome integrated into eukaryotic genome
Capsid
Protein coat enclosing and protecting nucleic acid
Viral envelope
Outer membrane layer, composed of host cell membranes, other membrane proteins, and viral glycoproteins
Bacteriophage
Viruses that infect bacterial cells
Additional structures of bacteriophages
Sheath
Tail fibers
Sheath of bacteriophage
Helps eject viral DNA into host
Tail fibers
Help with recoginition and attachment
Viral infections in humans
Acute
Chronic
Latent
Slow progressing
Acute infection
Rapid onset of symptoms and virion replication; brief and resolved in days
Chronic infection
Initial period of high viral load; reduced to low once immune system controls infection
Lasts several years to lifetime
Latent infection
Intermittent phases of high and low viral loads after initial acute
Lasts years to a lifetime
Slow progressing
Seems dormant after initial viral load but progresses (viral replication) years later
Defense against viruses
Cell surface mutations
Restriction enzymes
CRISPR- Cas system
Cell surface mutations
Prevents phages from identifying bacterial surface proteins
Restriction enzymes
Cut a specific recognized sequences to prevent replication if phage is inside the cell
CRISPR- Cas System
Internal defense of bacteria that recognizes and cuts out viral genomes
Viral outbreaks
Epidemics
Large population
Pandemic
Global impact
Vaccines
Weakened agents that mimic disease causing organism to stimulate immune system
Viral modifications
Antigenic shift
Viruses mix genes to increase host ranges, difficult to treat
Antigenic drift
Minor changes in viruses allow for infection of same host species
Infectious particles
Prions
Infectious misfolded proteins that cause other proteins to misfold into the prion form
Viroids
Single stranded RNA molecules that infect plants
Viral life cycle (bacteriophage)
Attachment, entry, uncoating, synthesis, self assembly, release
lytic cycle
Virus injetcts genetic material into host cell, hijacks cell machinery to produce more virus
New virus erupts from the host cell membrane and kills cell in process
Lysogenic cycle
Virus hides out in a host’s genome, viral DNA is incorporated into the DNA of the host cell
After dormant virus recieves a certain signal from the environment it undergoes the lytic cell and kills the cell
Provirus
dormant stage
Attachment in viral life cycle
Between host cell and specific viral surface proteins
Entry stage of life cycle
Bacteriophage inject genome into bactieral host cell using protein tail; enveloped viruses will fuse their viral envelopes with host membrane, and other viruses are taken in via endocytosis
Uncoating
Once inside host, viral genome is exposed via breakdown of viral capsid
Synthesis/ Replication
Virus replicated its genome and viral proteins; requires host’s nucleotides, enzymes, and ribosomes
Self assembly
Viral components spontaneously assemble into new complete viral particles called virions
Release
Where viral shedding allows newly replicated viral particles to leave host (via budding, apoptosis, exocytosis)
