1 Pathogens as parasites Flashcards
Bacteria are prokaryotes, all other organisms (except viruses/ prions) and eukaryotes
Describe structure of prokaryote
Describe structure of eukaryote
Prokaryotes -
Single circuclar chromosome (distinct nuculeus absent)
Plasmid (extrachromosomal DNA)
Cytoplasm
Ribosome
Cell membrane (site of cellular respiration)
Cell wall
Eukaryotes -
Nucleus containing chromosomes
Cytoplasm has mitochondria, endoplasmic reticulum, golgi apparatus, lysosymes
What is transcription/ translation?
How does this differ between prokaryotes and eukaryotes?
Transcription - DNA copied to mRNA
Translation - change mRNA into sequence of amino acids
Prokaryotes - transcription and translation can be carried out simultaneously
Eukaryotes -Transcription and translation carried out separately, with transcribed mRNA moving out of nucleus into cytoplasm for ribosomal translation
Prokaryotes have cell walls.
What is difference between gram positive and negative
Positive - peptidoglycan
Negative - outer layer of lipopolysaccharides
Microparasites (viruses, bacteria, protozoa, fungi) replicate within the host, and can produce large numbers of progeny.
Macroparasites (worms, arthropods) cannot do this. One infectious stage changes to one reproductive stage. Therefore level of infection determined by how many organisms initially infected.
Viruses live within cell. Which bacteria are also intracellular?
Chlamydia Rickettsia Listeria Salmonella enterica Brucella Mycobacterium TB
Trichinella - almost all other macroparasites are extracellular
What are benefits of being intracellular organism?
Difficulties of treating intracellular pathogens
Intracellular pathogens must become extracellular at some point, in order to replicate successfully they must leave the host cell
Evade host immune response - including antibodies.
Often live in immune cells e.g macrophages/ lymphocytes, thereby depressing the host response initially, and helps evade surveillance. Control relies on intracellular killing mechanisms, or cytotoxic agents which may also kill host cell
What are benefits of being an extracellular organisms
Larger supply of nutrients
Can spread quicker
Physical size e.g worms, means they cannot be phagocytosed
What are the three branches of phylogenetic tree of life
Classification being revolutionised by genome sequencing
Archaea - prokaryotes, which do not cause human disease
Eukaryotes - fungi, protozoa, helminths, arthropods
Prokaryotes - bacteria
Viruses/ prions are not alive, so not included
Describe how binomial classification works
It is a method of giving every species a name with two words. Does not include viruses/ prions
6 kingdoms in use: Archaea Bacteria Protista (eukaryotes which dont fit in 3 below e.g amoeba) Fungi Animals Plants
3 domains in use:
Archaea
Bacteria
Eukarya
Species e.g Homo sapien
Genus e.g Homo closely related, but not interbreeding species. Must start with capital
Family e.g Hominids
Order e.g Primates
Class e.g mammals
Phylum e.g chordates
Kingdom e.g animalia
Domain e.g eukarya
Homo (genus) sapiens (species)
How do structural and biological characteristics help sub-divide bacterial taxonomic groupings
Matrix-assisted laser desorption ionization time of flight (MALDI TOF) mass spectrometry can help identify organisms quickly
Staining - gram pos/ neg Shape - cocci/ bacilli Respiration - aerobic/ anaerobic Shape/ reproduction - clusters/ chains, sporing/ non-sporing Genus - Staphylococcus Species - S. Aureus
Cell wall, flagellar, and capsule antigens are used to define serogroups and serotypes
e.g samonella, streptococci, shigella, E. Coli
Biochemical characteristics can be used to define subspecies groupings - biotypes, strains, groups. E.g staph aureus typically releases beta-haemolysin
Production of toxins can also help differentiate e.g E. Coli
Viruses may be named according to the associated diseases (poliovirus, rabies), the type of disease caused (murine leukemia virus), or the sites in the body affected or from which the virus was first isolated (rhinovirus, adenovirus). Some viruses are named for where they were first isolated (Sendai virus, Coxsackievirus), for the scientists who discovered them (Epstein-Barr virus), or for the way people imagined they were contracted (dengue = ‘evil spirit’; influenza = ‘influence’ of bad air).
There are multiple disputed classification systems.
What is one basis of viral classification
Nature of the nucleic acid in the virion - e.g DNA
Symmetry of the protein shell e.g icosahedral
Capsid naked/ enveloped
Dimensions of the virion and capsid
What determines pathogens virulence?
Structural/ biochemical/ genetic features which enable it to cause disease in man
Infection is interplay between virulence and host defense/ immunity
