Cell Division Flashcards
What are the major groups of microbes studied by microbiologists?
Prokaryotes eg. bacteria Eukaryotes eg. algae Viruses Archaea Protists Fungi
How do microbes affect human history?
Food availability- destroy crops, but preserve food eg. bread, wine, cheese, chocolate.
Microbial diseases eg. black plague in Europe, Smallpox in Americas.
How were microbes first discovered?
Light microscope invented in the 1600s.
Robert Hooke observes small eukaryotes, and he is credited with being the first to discover small microbes.
Why is Anton van Leeuwenhoek important?
He was a Dutch scientist who invented the first compound micoscope. He was the first to observe living cells- blood cells and protists. Discovered bacteria (prokaryotes) in 1676.
What proof is there that microbe arise only from other microbes?
There is no spontaneous generation:
1688- Redi showed that flies don’t spontaneously generate.
1861- Pasteur showed that microbes don’t grow in liquid until introduced from outside.
Wouldn’t grow in sterile liquid unless something else was introduced.
What makes microbial species difficult to classify?
Difficult to distinguish by shape- many are similar.
Often reproduce asexually.
Pass DNA to each other without reproduction.
How are microbial species classified?
Biochemical properties- Gram stain, ability to metabolise different substrates.
DNA sequence- bacterial genomes are relatively small.
How are bacteria similar and different to archaea?
Similar shape and size, but very different biochemistry.
Describe Gram positive and Gram negative cells.
Gram positive have one membrane and a thick cell wall made of peptidoglycan.
Gram negative have two membranes, an inner and outer one, with periplasm in between. The peptidoglycan cell wall is in between the membranes, above the periplasm.
Describe the different bacterial shapes, arrangements and sizes, and why they are important.
Coccus- spherical. Bacillus- Rod: - coccobacillus- very short and plump (Brucella abortus) -streptobacilli (Bacillus subtilis) - Diplobacilli Spirillum- helical, comma, twisted rod: -spirochete- spring-like, flexible (Treponema pallidum) -vibrio- gently curved (Vibrio cholera) -spirilla- rigid (Borrelia species) Pleomorphic- variable in shape (Corynebacterium). Polar flagella- all at one end. Peritrichous flagella- all over.
Influences how they grow and propagate.
What are the subdivisions of cocci?
Diplococci- remain in pairs after dividing.
Streptococci- remain in chains after dividing.
Tetrads- divide in two planes and remain in groups of four.
Sarcinae- divide in three planes and remain in cube-like groups if eight.
Shaphylococci- divide in multiple planes and form grape-like clusters or sheets.
What are the subdivisions of bacilli?
Most are single rods.
Diplobacilli- pairs after division.
Streptobacilli- chains after division.
Coccobacilli- ones taht are so short and fat that they look like cocci.
How goes microbial growth work?
Increase in cell number, not cell size.
One cell becomes a colony of millions of cells- arise from one microbe.
Describe the dilution and plating method?
Direct method.
Grow a culture, then create a serial dilution set (usually by adding 100ul sample to 900ul solution to make 1ml culture, then take 100ul culture one to culture two etc). Plate dilutions, spead evenly and incubate. Use dilutions that grew a good number of clear colonies to work out CFUs per ml.
(can look for antibiotic resistance).
What is the cell counting method?
Culture added onto grid of 25 squares. Culture fills volume over squares by capillary action. Depth under cover glass and area of squares are known, so bacterial suspension can be calculated (depth x area). All cells in squares are counted and averaged. Calculation can be done.
Count how many colonies you see. Can use a light or electron microscope. Count live and dead cells.
How is spectrophotometry used in bacterial number estimation? What are some problems?
Indirect method. Measures turbidity (measure of water clarity- material suspended in water that disturbs light passage). Optical density (measure of amount of light absorbed by bacterial suspension) is a function of cell number.
Medium may not be completely clear. Bacteria may be in aggregates. Bacteria may be photoreceptive. Bacteria can make molecules eg. polysaccharides and proteins which can interfere and gives false readings.
Give an example of measuring metabolic activity and why it is good?
Measuring of carbon dioxide production during fermentation.
Can look at under different growth conditions.
What is dry weight measurement, and what are some problems with it?
Measurement of dry weight when individual cells/colonies can’t be distinguished as they are too dense or aggregated.
Not very accurate or time consuming, but sometimes only option eg. fungal filaments.
What are the environmental limits on microbial growth?
Nutrient source, temperature, pH, osmolarity, oxygen, pressure.
Different optimum conditions for each species.
What are the phases involved in bacterial growth and food availability?
What happens in each phase?
What do bacterial cells do when food is low?
Lag phase- bacteral growth low, food high.
Log phase- bacterial growth increases, food decreases.
Declining growth phase- bacterial growth starts to plateau, food decreases more.
Endogenous repiration phase- bacterial growth starts to decrease, food is low.
Food to mass ratio decreases throughout each stage.
Sporulation in conditions of nutrient stress. Ensure genetic line is safe. (eg. B.subtilis) Can be viable but non-culturable.
Programmed cell death.
Dormancy.
