Prokaryotes Flashcards

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1
Q

what are prokaryotes?

A

Microscopic single-celled organism which has neither a distinct nucleus with a membrane nor other specialized organelles

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2
Q

How have prokaryotes survived all these years in an oxygen rich atmosphere?

A

They can survive in extreme environments such as the pink lakes which have a high salt concentration

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3
Q

Where are some places or some environments that prokaryotes can survive?

A
  • exposure to 3 million rads (3000× fatal dose for humans)
  • pH 0.03 (which is acidic enough to dissolve metals)
  • near volcanic vents and has an optimal growth temperature of 100C
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4
Q

What are the three main shapes of prokaryotes? What are their size ranges?

A

» Spherical (“coccus”)
» Rod-shaped (“bacillus”)
» Spiral (“spiro-”)
- Small (0.5 – 5 µm)

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5
Q

What are the benefits of a cell wall for prokaryotes and what are the different types?

A
  • Provides protection against osmotic stress
  • Bacterial cell walls contain peptidoglycan (sugar and polypeptide)
  • Some have naked cell wall (“gram-positive”), others have an additional cell membrane on top of the cell wall (“gram-negative”)
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6
Q

What is a gram stain and what does gram-positive and gram-negative mean?

A

a staining technique for the preliminary identification of bacteria, in which a violet dye is applied, followed by a decolorizing agent and then a red dye. The cell walls of certain bacteria (denoted Gram-positive ) retain the first dye and appear violet, while those that lose it (denoted Gram-negative ) appear red.

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7
Q

What is a polysaccharide and capsule?

A

In many prokaryotes, the cell wall is surrounded by a sticky layer of polysaccharide or protein called capsule

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8
Q

What is the purpose of polysaccharide and capsule?

A

Enables bacteria to “stick” to substrate

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9
Q

What are fimbriae

A

Hairlike appendages on the outside of the cell wall of a bacteria

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10
Q

What is an endospore

A

» Formed when faced with harsh conditions
» Highly protective, multilayer coat forms around the chromosome, water is removed and metabolism stops …
» Can remain dormant and survive until conditions are favourable again

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11
Q

What are Flagellum

A

(pl. flagella)
» Allows prokaryotes to move (up to 50× their body length per second!)
» Works like a propeller

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12
Q

Where does the genetic diversity of prokaryotes come from?

A

Result of combination of 3 main factors:
» Rapid reproduction (some as fast as 20 min)
» Mutation due to error in replication (“1 in a million, but a million comes quickly!”)
» Genetic recombination (uptake and integration of foreign DNA, including exchange of plasmids)

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13
Q

What is conjugation

A

The temporary union of two bacteria or unicellular organisms for the exchange of genetic material.

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14
Q

What is recombination

A

Rearrangement of genetic material, especially by crossing over in chromosomes or by the artificial joining of segments of DNA from different organisms.

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15
Q

What was the first known case of antibiotic resistance

A

Japan (1950s): some hospital patients with bacterial-induced diarrhoea did not respond to antibiotic treatment → some strains of bacteria have mutations that make them resistant to antibiotic

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16
Q

How did antibiotic resistance happen and what effect does this have on humans

A

Exposing bacteria to specific antibiotic kill the “normal” bacteria, leaving only the resistant mutants … which then grow without competition!

  • Over-use of antibiotics is creating “superbugs”, which have multiple resistance genes
  • Significant environmental threat to human survival
17
Q

Where do prokaryotes get their nutrition?

A
  • Astounding range of nutritional and metabolic adaptations
  • Part of the success of prokaryotes
  • All four major modes of nutrition:
    Photoautotrophs
    Chemoautotrophs
    Photoheterotrophs
    Chemoheterotrophs
18
Q

What are “Obligate aerobes”?

A

Prokaryotes that must use O2 for cellular respiration.

19
Q

What are “Obligate anerobes”?

A

Prokaryotes that are poisoned by O2, and either use another terminal electron acceptor (NO3- or SO4^2-) or only conduct fermentation

20
Q

What are “Facultative aerobes”?

A

Prokaryotes that are very flexible and can work in either aerobic or anaerobic environments

21
Q

What is nitrogen fixation?

A

N is essential for production of amino acids and nucleic acids in all organisms
- Prokaryotes (unlike eukaryotes) can get that N in many forms.
- Some prokaryotes (cyanobacteria and methanogens) incorporate N2 straight from atmosphere into ammonia (NH3)
» Critical for plants, who form symbiosis with these nitrogen-fixing prokaryotes to increase available N

22
Q

What domain contains most of the prokaryotes?

A

domain bacteria

23
Q

What are the five clades in domain bacteria based on molecular (DNA) data?

A

» Proteobacteria: very diverse clade, incl. nitrogen fixing bacteria
» Chlamydias: parasitic bacteria, survive only in animal cells, depend on host for resources as basic as ATP (!)
» Spirochetes: spiral, most free-living, some pathogenic parasites (eg Treponema pallidum → syphilis)
» Cyanobacteria: only prokaryotes with plant-like oxygen-generating photosynthesis (likely related to chloroplasts)
» Gram-Positive Bacteria: very diverse clade, incl. Streptomyces (→ antibiotic “streptomycin”)

24
Q

What is Domain Archaea?

A
  • Archae share traits with Bacteria and Eukarya and some are unique
  • Phylogeny still uncertain
  • Archae include:
    » “Extremophiles”: grow in extreme salt or temperature environments
    » “Methanogens”: decomposers (herbivore
    intestines, sewage treatment plants …)
25
Q

What are the ecological roles that prokaryotes play in chemical recycling?

A

» Chemoheterotrophic prokaryotes break down dead organisms and organic matter → releases C, N and other elements
» Autotrophic bacteria fix CO2 to make organic compounds, which are then passed up the food chain
» Nitrogen-fixing prokaryotes fix atmospheric N (N2) into forms that other organisms can use

26
Q

What are the ecological roles that prokaryotes play in ecological relationships?

A

» Mutualist (+/+) (eg bioluminescence, gut bacteria)
» Commensal (+/0) (eg skin bacteria)
» Parasitic (+/-) (eg pathogenic bacteria)

27
Q

How do prokaryotes affect humans beneficially?

A
  • Mutualistic bacteria (+/+)
    » >500 species of bacteria in gut (“microbiome”)
    » Maximise energy intake from food
    » Synthesise essential carbohydrates, vitamins and other nutrients
    • Vitamin B7 (biotin)
    • Vitamin K1 → Vitamin K2
28
Q

How do prokaryotes affect humans negatively?

A

Pathogenic bacteria (+/-)
» All pathogenic prokaryotes are Bacteria
» Bacteria cause about 50% of all human diseases
• >1 million people die each year of tuberculosis (caused by Mycobacterium tuberculosis)
• 2 million people die each year of diarrhoeal diseases caused by various bacteria (eg Salmonella)
• Syphilis, bubonic plague (“black death”), typhoid fever, leprosy, Lyme disease, cholera, tetanus, diphtheria, bacterial pneumonia, scarlet fever, tooth decay

29
Q

How do humans use prokaryotes?

A
  • Bacteria convert milk → cheese and yoghurt - Some bacteria (like E. coli) are widely used in genetic research and engineering
  • Some bacteria used for bioremediation
    » Anaerobic bacteria and archae used in sewage treatment
    » Oil spills: some bacteria “eat” oils
    » Radioactive spills: some resistant bacteria can fix radioactive isotopes