viruses and pathogens Flashcards
(27 cards)
what are viruses?
obligatory parasites
this means that they need to use the metabolic machineries of a host to replicate
they are typically small but vary in size
what do all viruses contain?
a nucleic acid genome surrounded by a capsid protein which is all contained within a lipid envelope
what is the structure of the viral genome?
it can be made up of DNA or RNA and it can be double or single stranded
single stranded RNA genomes can be positive or negative
they only need specific genes because they use the genetic information of the host
the genome is usually one molecule that is fragmented
what is the structure of the viral capsid?
made up of proteins called capsomers
the proteins self-assemble into a highly ordered symmetrical structure that can either be icosahedral (spherical) or helical (rod shaped)
what is the structure of the viral envelope?
made up of lipids and glycoproteins
some viruses have a spike protein embedded in the envelope that binds to the host cell receptors
the envelope is made up of lipids found in eukaryotic cells making it easier for the virus to fuse
what is the structure of bacteriophages?
they have complex morphologies that contain a mixture of icosahedral and filamentous structures
they have a base plate on the head (which contains the genome) that attaches to the host cell via fibres that extend from it
the have a tail that injects genetic material into the host
how does baltimore classification group viruses?
by the nature of the genome, the genome replication mechanism and the type of RNA or DNA
what are the disadvantages of grouping viruses by baltimore classification?
it doesn’t reflect the evolutionary history of the bacteria
bacteria with the same genome can have different morphologies or pathogenicies
what do viruses need for translation?
a single positive strand of mRNA
what are the 5 main stages in the life cycle of viruses?
- attachment to the host cell
- injection of the genome
- production of nucleic acid and proteins
- assembly of viral particles
- release of the virus
what are bacteriophages?
a virus that infects bacteria
what are the 2 classes of bacteriophages?
virulence/lytic phages
temperate/lysogenic phages
how do virulent phages infect and replicate within a host cell?
- they attach to the host cell and inject their genome into it
- the phage DNA will circle around and hijack the host’s transcription and translation mechanisms to produce RNA and proteins
- the viral particles assemble into virions and then a protein within the phage genome integrates into the host cell membrane to form pores
- enzymes in the membrane hydrolyse peptidoglycan causing the cell to lyse and release phage virions
how do viruses with a lipid envelope enter a host cell?
the glycoproteins will recognise and bind to receptors on the host cell
how do viruses with a capsid enter the host cell?
it is engulfed by the host cell into the cytoplasm
what are the 3 enzymes in retroviruses?
reverse transcriptase, integrase and protease
what is the role of integrase and protease in retroviruses?
integrase is used to integrate the viral DNA into the host’s genome
protease is used to produce viral proteins
what is a pathogen and what is pathogenesis?
a pathogen is any agent that can cause a disease e.g. bacteria, viruses, fungi, protozoa and prions (not archaea)
pathogenesis is a survival strategy where pathogens use resources from other organisms to survive
how do pathogens in our body cause disease?
we all have active, properly folded proteins in our body
if we come into contact with the variant protein that is incorrectly folded it can trigger our proteins to misfold and become pathogens that cause a disease
what are the 5 criteria for a successful pathogen?
- they have to gain access to a host through a portal of entry e.g. mouth or eyes
- they have to locate a nutritionally compatible niche
- they have to avoid the immune systems of the host
- they have to access the host’s resources and replicate which then causes an infection
- they have to exit the host and spread to a new host
why does not all exposure to pathogens cause infection?
the pathogen has to replicate in the host to cause disease
what is virulence?
the measure of how severe a disease is
what are the 3 measures of virulence?
mortality: number of deaths from a disease
morbidity: number of cases of a disease in a population
infectious dose: number of individual particles or cells required for infection
why is having a high virulence not good for a pathogen?
because it causes the host to die so the resources are lost and the pathogens die
