1.2 - Intro to Microbes Flashcards
What is a prion
Abnormal pathogenic agents that are transmissible and are able to induce abnormal folding of specific normal cellular proteins
☞ form abnormal aggregates of proteins amyloids which accumulate in infected tissue and are associated with tissue damage and death
Basic constituents of a virus
- capsid is a protective protein shell
- spikes are protein markers studded into envelope – attach to specific cell surfaces
- envelope some have this: lipid membrane. The presence of this affects how robust they are
- genetic material genetic code – DNA or RNA
What are the different classifications of DNA + RNA viruses
DNA
- single or double stranded
- enveloped or non-enveloped (this affects how robust they are)
RNA
- single stranded or double stranded
- if single stranded: is it negative or positive
- helical or icosahedral
Bacteriophages
- these are viruses that infect bacteria
- these can kill bacteria
- mainly protein head, collar and tail with long tail fibres and base plate
- DNA encased in protein head
- May be able to be used as a therapeutic agent
Basic constituents of a bacterial cell
- capsule made of polysaccharide, protecting bacteria from toxins and allowing them to adhere to surfaces
- cell wall made of peptidoglycan aka murein
- Plasma membrane
- Cytoplasm
- Ribosomes
- Plasmid: small circular loops of DNA
- Pili for mediation of cell-cell interactions, motility and DNA uptake
- Flagellum
- nucleoid made of circular, single stranded DNA
What are the different shapes of bacteria
- coccus aka circular or oval, and plural = cocci. Can be arranged in clusters or chains
- spirillus like a helical structure
- bacillus aka rods, plural = bacilli
Arrangement of cocci
- Can be found singly
- In pairs = diplococci
- In groups of 4 = tetrad
- In clusters = stapylococci
- In chains = streptococci
Gram positive vs gram negative bacteria
☞ distinguished based on structure of cell walls + their reaction to gram staining
gram positive = cell walls made of thick layer of murein. Have a plasma membrane but no outer membrane. Stains purple
gram negative = cell walls made of a thin layer of murein. Also have an outer membrane (and plasma membrane). Stains red
Oxygen tolerance – aerobes vs anaerobes
aerobes can survive in the presence of oxygen. Obligate aerobes require oxygen for survival.
anaerobes can survive in the absence of oxygen. Obligate anaerobes require oxygen-free environment for survival (unless able to form spores).
What are spores
a minute, typically unicellular, reproductive unit capable of developing into a new individual without fusion with another reproductive cell
☞ able to withstand extremes eg temperature, pressure and chemicals
How are bacteria named
Using linnaean taxonomy Genus + species
▶︎ names are sometimes supplemented by adjectives describing growth, or other characteristics
Mechanisms of bacterial pathogenesis
virulence factors
- Host entry (ie polysaccharide capsule)
- Adherence to host cells (ie using pili)
- Invasiveness (ie enzymes)
- Iron sequestration (using siderophores – more on sep card)
toxins
endotoxins + exotoxins (more on sep card)
what are siderophores
- Often secreted by bacteria
- They scavenge iron from the extracellular environment
- Act as an iron chelating agent
- Take away iron from the host, and provide this instead to microbes
what is the difference between endotoxins and exotoxins
exotoxins are proteins produced inside pathogenic bacteria which are secreted into the surrounding medium.
endotoxins are constitutive elements of the bacteria membrane. They are only freed when the bacteria die.
Prokaryotes vs eukaryotes
prokaryotes
- Circular, usually single chromosome
- extra-chromosomal DNA may also be present (plasmids)
- no nuclear envelope or nucleoli
- no membrane-bound organelles
- usually have murein cell wall
- have a plasma membrane, but lacks carbohydrates and sterols
- 70S ribosome
eukaryotes
- Multiple chromosomes
- Membrane bound nucleus + with nucleoli
- Membrane bound organelles eg mitochondria and ER
- Cell walls present in plant cells, but cellulose
- Have plasma membrane, sterols and carbohydrates are present
- 80S ribosome (70S in organelles)
