microbes and the immune system Flashcards
symbiosis
= symbiotic relationship involves the association of 2 or more partners
symbiotic relationship
mutualism
= both organisms benefit.
bacteria examples:
- colonic bacteria provided with a niche in the host
- Ruminococcus spp. can be found in high numbers in the gut and involved in cellulose breakdown.
fungi examples:
- fungi attach to the roots and allow root extension, in exchange the plant provides sugars to the fungi.
commensalism
= one organism benefits and the other neither benefits or is harmed.
example: - Staphylococcus epidermidis utilises dead skin cells without causing harm
parasitism
= one organism benefits at the expense of the other
- parasitic microbe lives or multiplies within/on the host, causing damage in the process
example: malaria -> plasmodium falciparum
opportunistic pathogen
a pathogen that does not normally cause disease, only causes disease when the host’s defences are compromised
example: cold sores - herpes simplex virus
primary pathogen
can cause disease in a host regardless of the host’s immune system state, or barriers.
Koch’s postulates- traditional
= koch’s postulates are a set of criteria that establish whether a particular organism is the cause of a particular disease.
traditional states that:
- pathogen must be absent in all healthy individuals but present in all diseased hosts.
- pathogen must be isolated and grown in pure culture
- it must cause the same disease if introduced into a healthy host
limitations:
assumes all organisms can be cultured in a lab
ethical issues infecting healthy hosts ]
doesnt explain disease caused by multiple pathogens or pathogens that can live in healthy hosts
modern Koch’s postulates
- isolation of genetic material enables pathogen identification
- specific genes correlate with disease
- used to determine what genes contribute to a pathogen’s ability to cause disease
- some pathogens can exist in healthy individuals which conflicts the traditional way.
what is pathogenicity, phenotypic switching and virulence?
pathogenicity = the ability to cause disease
virulence = the degree of pathogenicity of an organism (infectvity/ intensity)
phenotypic switching = changing appearance depending on the environment it is in, increased invasion as can get passed the defense in alternative form.
identification tools for microbes
1.) agar plates (culture method, however is not suitable for all organisms)
2.) molecular techniques (OMICS)
- genomics (can identify genes and organisms from DNA)
- transcriptomics( tells you parts of DNA that have been expressed, to allow protein production from RNA)
- proteomics( what proteins are produced)
- metabolics( metabolites produced by a population living together)
3,) microarray technology ( tells you what genes are expressed within each population using florescence, a general laboratory technique)
viral replication process
1.) attatchment of virus to host cell through specific receptors
2. virus enters host cell
3. the viral genome is replicated
4. viral genomes are transcribed and translated by host cells ribosome (gene expression)
5. assembly of viral genomes and proteins
6. release from host cell, to infect new cells.
genetic properties of RNA
- uses uracil instead of thymine
- nuclear and cytoplasmic
- OH at 2’ ribose position
- short term storage
- small genome size
- low intrinsic stability ( reactive to neighbouring dipoles)
- single stranded (either a positive or negative strand)
- low polymerase fidelity (ability to replicate a template)
- low error correction
genetic properties of DNA
- uses thymine
- mainly found in nucleus
- H at ribose 2’ (no oxygen)
- long term storage
- high intrinsic stability (less reactive, cos no O)
- large genome size
- high polymerase fidelity
- high error correction
differences between DNA and RNA viruses in terms of: genome size & organisation; infection cycle; antigenic drift and shift; recombination & mimicry; latency
Genome: DNA viruses have larger, stable genomes; RNA viruses have smaller, mutation-prone genomes.
Infection Cycle: DNA viruses often replicate in the nucleus, RNA viruses usually in the cytoplasm.
Antigenic Variation: RNA viruses exhibit frequent antigenic drift and more opportunities for antigenic shift.
Recombination & Mimicry: Both types can recombine and mimic host molecules, but mechanisms differ.
Latency: DNA viruses are more likely to establish long-term latency, while RNA viruses are typically associated with acute infections.
Antigenic shift and drift: RNA viruses are more prone to these changes due to their high mutation rates and segmented genomes.
RNA viruses have faster evolution capacity -> rapid adaptation, they also have greater coding capacity
antigenic shift
= a major alteration in antigen sequence by a process of genome reassortment (segmented virus) or inner strain recombination that results in a new strain of the virus. (sudden change in genetic makeup)
antigenic drift
- virus undergoes a gradual change in genetic makeup, causing a different, but somewhat similar genetic makeup to the parent virus.
- antigens accumulate small mutations, is these are advantageous, will become predominant through selective pressures
segmented virus
Viruses that packages all of their genome segments into a single particle. This allows the virus to be infective.
- they can have multiple segments ( encoded genes are divided across molecules of DNA or RNA)
recombination
= allows for major alterations through exchange of genetic material between viruses or with the host
- genetic exchanges between a pair of homologous DNA sequences
viral mimicry
= stealing from the host
- can disable the immune system with decoys which is:
- favoured by the large size of DNA viral genomes
- favoured by DNA-DNA host virus recombination
