Viruses Flashcards
Diversity of Structure in Viruses
Genetic material can be DNA or RNA, and single or double stranded
Some viruses have a lipid envelope and some don’t
Different shapes: threadlike, polyhedral, spherical
Reasons for High Evolution Rate
High mutation rates: Viruses have RNA as their genetic material so mutations can occur during the reverse transcriptase process of turning RNA into DNA
Large population sizes
Short generation times
Structural Features Common to All Viruses
Small size, don’t form large structures
Fixed size, they don’t grow
Nucleic acid core, genomes are made of RNA or DNA
Protein coat Capsid, attachment proteins on the outer surface to allow viruses to bind and enter host cells
No cytoplasm and very few enzymes
Lysogenic Cycle
During the lysogenic pathway the viral nucleic acid combines with the host DNA turning into prophage
However, a viral gene coding for a repressor protein prevents the viral nucleic acid from being transcribed thus making it dormant
The host cell will continue to function as normal, reproducing and undergoing cell division with the virus nucleic acid in the host’s genome
Changes in the environment triggers the viral DNA to enter the lytic pathway and to inactivate the repressor protein, thus entering the lytic cycle
Treating Diseases Caused by Antigenic Shift and Drift
Vaccines need to be changed and updated yearly so they remain effective for viruses that undergo antigenic drift as the changes aren’t rapid
For viruses undergoing antigenic shift, vaccines aren’t useful as changes are rapid and unpredictable, so it may need to be dealt with isolation of infected individuals (quarantine) to stop the spread of the infection
Bacteriophage Lambda Characteristics
Infects E.coli
Double stranded DNA within capsid head
Tail and fibrils allow it to attach to host and insert DNA into the cell
Tail consists of proteins that contract which allows virus to move the tail through E.coli cell wall
DNA is injected into host cell through tail
Lytic Cycle (Bacteriophage Lambda)
Virus attaches to the cell membrane of the host cell using attachment proteins on its tail
Virus infects the host cell by injecting its DNA into the cytoplasm
Virus then uses proteins and enzymes within the host cell to produce new virus particles through biosynthesis
Virus particles are assembled and are matured into VIRIONS
Host cell then undergoes lysis, releasing the virions into the host organism to infect more cells
Antigenic Drift
Accumulation of small changes to viral genetic material over time
Variation in the surface proteins of the virus appear slowly, and the host’s immune system will eventually not recognize the virus
HIV
Escape Theory
Viruses were originally DNA and RNA that gained the ability to move between cells, but they got surrounded by an outer boundary forming a virus particle
Human Immunodeficiency Virus (HIV) Characteristics
Two RNA strands
Spherical shape
Envelope consists of lipid bilayer and glycoproteins that act as attachment proteins
Have protein called reverse transcriptase that turns RNA into DNA
Known as a Retrovirus
Virus-first Theory
Viruses started as simple, self-replicating genetic material that could copy themselves, but they weren’t cells. As cells evolved, these early viruses became parasites, adapting to infect cells to survive and replicate.
Classification of Viruses
Infectous particles
Not organisms as they’re not considered to be alive
Have no cellular structure
Have no metabolism
Are acellular
Parasitic
Do not respire
Specific to each host
Coronavirus Characteristics
Cause respiratory disease in mammals and birds
Single stranded RNA
Spherical shape
Envelope outside capsid, with many glycoproteins that project from their surface making a corona
Antigenic Shift
A major change that occurs in viral genetic material in a short time period
Variation in the surface proteins of the virus appear rapidly, and a new virus is created which the host’s immune system can not recognize
Influenza
Regressive / Reduction Theory
Viruses are remnants of cellular organisms or were once small cells that became parasites of larger cells, and over time the cellular structures were no longer needed and got shed which left the viral structure only
