Introduction to Microbiology Flashcards
overview of earth formation
- 4.5Gy = supernova created the sun and planets
- 4.0Gy = apparition of water and atmosphere
- 3.9Gy = earth cooled down and water condensed to form oceans
- oldest sedimentary rocks formed
- 3.5Gy = stromatolites were formed
- bacterial communities lived in sediment layers
- Microfossils
- first experimental evidence that life started around 3.5Gy
what is the prebiotic soup model?
This model suggests that the chemically reducing atmosphere of the earth produced simple organic monomers. These monomers accumulated in a ‘soup’, producing complex polymers, and eventually life
all building blocks of life can be produced from the same pool of compounds under certain conditions;
- hydrogen cyanide (HCN)
- hydrogen sulphide (H2S)
What was Miller’s experiment?
An atmosphere that mimicked the atmosphere of early earth was produced by mixing water vapour, methane, molecular hydrogen and ammonia with electrical discharges.
A week later, organic compounds like amino acids were produced
limitations: no evidence of amino acids present in sediments, and the atmosphere had a higher H2 concentration than what was used in the experiment
what is the RNA world hypothesis
RNA could have been the first macromolecule encoding complex info:
- requires less energy than DNA to form/degrade as unwinding isnt required
- some viruses use ssRNA as genetic material
- RNA have have catalytic properties - ribozymes = splicing
How did compartmentalisation lead to LUCA? (apparition of cellular life)
Hypothesis 1: surface origin
- primitive cells were formed spontaneously on earth from prebiotic soup
- natural selection led to optimise metabolic process
Hypothesis 2: subsurface origin
- life appeared in hydrothermal mounds on ocean floor
- geothermally heated water from fissure, and cool ocean water formed montmorillonite clays
- H2 and H2S provided electrons to form organic molecules
what is the panspermia theory?
life originated from space and that evolution is driven by viruses from space e.g. spanish flu
who introduced the nomenclature for the 3 domains of life?
Carl Woese: he intoduced Bacteria, Archaea and Eukarya, defining a new taxon
How does gene plasticity cause microbial diversity?
Haploid genome creates diversity:
- bacteria only have one chromosome, so mutations are easily passed on
Rapid multiplication means population can double within 20 minutes
- 10 hours -> 1 billion cells
Gene transfer: transformation, transduction, conjugation
what is taxonomy?
discipline which deals with classification of organisms
- species are defined according to a taxonomic hierarchy + common phenotypes
- uses binomial nomenclature
Describe phenotypic analyses used in taxonomy:
- morphology/staining
- direct observations
- limited as morphology can change depending on environment - metabolic properties
- biochemical tests on unknown bacteria produce an ID value after incubation which can be compared to a computerised list to identify the bacteria - phage typing
- phages identify species by targeting specific organisms on agar plate
- lysis plaques are zones of bacteria which have been lysed by phages - fatty acid profiles
- fatty acids are extracted from bacterial culture and gas chromatography forms peaks which can be compared on database - mass spectrometry
- surface proteins produce a finger print of molecules associated with that organism which can be compared on database
describe genotypic analyses used in taxonomy:
- DNA hybridisation
- comparision of 2 species by seeing hoe much their DNA can hybridise by denaturing them and mixing them together
- no. H bonds formed indicates how closely they are related - FISH
- gene is labelled and hybridised with DNA in sample, and can see which organisms have that gene - MLST/fingerprinting
- housekeeping genes are selected and sequenced to compare alleles of different genes
- barcode is formed which can be compared with other species - whole genome sequencing
- samples are prepared and sent to a company
what is phylogeny?
studies evolutionary history and relationships of organisms
- achieved by comparing DNA and using rRNA sequences called molecular clocks
- housekeeping genes are required across many organisms for comparison
- forms phylogenetic trees which is based on a comparative analysis of the rRNA gene sequence
name some unicellular eukaryotes:
Fungi: - yeasts = unicellular - molds = filamentous - basidiomycetes = mushrooms can be multicellular
protists:
- unicellular algae (plant-like)
- protozoa (animal-like)
- slime molds
General properties of fungi:
- cell walls made of chitin, mannans and/or glucans
- most form multicellular filaments called hyphae (pleiomorphic)
- 2 phases in life cycle involving asexual and sexual reproduction to form spores (resistant)
- undergo transitions between unicellular and multicellular forms
why are fungi important?
- contribute to carbon cycle as they are decomposers
- can be plant pathogens and spoil 10-30% of crops
- loss of £150 billion/year
- penicillin is extracted from mold
- fungal infections cause over 1.5 million deaths per year
