A2.3 Viruses Flashcards
List structural features common to all viruses
Small
Non living
Contain nucleic acids (DNA or RNA) and a capsid
Obligate intracellular parasites
Outline the diversity of structure in viruses, including genetic material and the presence or absence of envelopes.
1.5 micrometers to 0.018- 0.028 micrometers
DNA or RNA as genetic material
Single or double stranded genome
Circular or linear genome
Size of genome
Shape of capsid
Presence of a lipid envelope
Distinguish between negative-sense RNA, positive sense RNA, retroviruses and DNA viruses.
Negative sense RNA : RNA first transcribed before being translated into virus proteins.
Positive sense RNA : viral mRNA which can translate directly to virus proteins
Retroviruses : RNA that needs to be reverse transcribed into DNA. This DNA is then transcribed and translated to make virus proteins
Compare the structure of bacteriophage lambda, coronaviruses and HIV.
Bacteriophage Lambda
Host : E coli bacteria
Genetic material : Double stranded linear DNA
Structure : Complex capsid structure with an icosahedral head bound to a helical tail. Non enveloped.
Lifecycle : Alternates between lytic and lysogenic
Associated Human Disease : None
SARS - CoV 2
Host : Mammal epithelium cells w/ ACE2 receptor protein
Genetic Material : Single stranded, linear, positive sense RNA
Structure : Complex capsid composed of helical nucleocapsid, icosahedral structure with distinctive club shaped spikes
Lifecycle : Lytic
Associated Human Disease : COVID -19
Human Immunodeficiency Virus (HIV)
Host : Primate T-cells with a CD4 receptor protein
Genetic Material : Two copies of single stranded RNA
Structure : Icosahedral capsid with an envelope. HIV has an enzyme capable of making a DNA copy of the viral RNA, which is then integrated into a host DNA
Lifecycle : Lytic
Associated Human Disease : Acquired Immunodeficiency Syndrome (AIDS)
Outline the phases of the lytic cycle of a bacteriophage lambda virus.
- Phage attaches to host cell
- Phage DNA enters the cell
- Phage DNA replicates
- Phage protein synthesis
- Assembly of new phage viruses
- Lysis
- Spread
State that in the lytic cycle, a virus relies on a host cell for energy supply, nutrition, protein synthesis and other life functions.
A virus relies on a host cell for energy supply, nutrition, protein synthesis and other functions
Compare the lytic system to the lysogenic cycle of a virus.
Lytic system breaks the host cell whereas the lysogenic cycle infects daughter cells
State that a temperate virus can alternate between a lytic and lysogenic cycle.
A temperate virus can alternate between a lytic and lysogenic cycle
Outline the phases of the lysogenic cycle of a virus.
- Phage attaches to cell
- Phage DNA enters the cell
- Phage DNA integrates within the cell’s DNA
- Cell divides and now future generations are infected
Outline evidence that viruses evolved after the origin of cells.
Viruses are obligate intracellular parasites meaning they require a host cell to evolve if viruses were first then they would not have any host to replicate in
Outline the progressive and regressive hypotheses for the origin of viruses.
progressive hypothesis is that viruses arose by taking and modifying cell components
regressive hypothesis is that viruses arose by loss of cellular components
Outline how convergent evolution could result in the commonality of some structures shared by viruses.
Because convergent evolution means that viruses evolved to share common features because of their similar environments
Outline three reasons for rapid evolution in viruses.
Short generation times.
Viruses have higher rates of mutation (especially RNA)
Large population size
Discuss the consequences of rapid virus evolution on treating diseases caused by viruses (influenza and HIV).
Infections are hard to cure because HIV due to natural selection will develop new variants.
