Prokaryotes

Question 1

what are prokaryotes?

Answer 1

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

Question 2

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

Answer 2

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

Question 3

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

Answer 3

• 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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

• 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”)

Question 6

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

Answer 6

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.

Question 7

What is a polysaccharide and capsule?

Answer 7

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

Question 8

What is the purpose of polysaccharide and capsule?

Answer 8

Enables bacteria to “stick” to substrate

Question 9

What are fimbriae

Answer 9

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

Question 10

What is an endospore

Answer 10

» 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

Question 11

What are Flagellum

Answer 11

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

Question 12

Where does the genetic diversity of prokaryotes come from?

Answer 12

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)

Question 13

What is conjugation

Answer 13

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

Question 14

What is recombination

Answer 14

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

Question 15

What was the first known case of antibiotic resistance

Answer 15

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

Question 16

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

Answer 16

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

Question 17

Where do prokaryotes get their nutrition?

Answer 17

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

Question 18

What are “Obligate aerobes”?

Answer 18

Prokaryotes that must use O2 for cellular respiration.

Question 19

What are “Obligate anerobes”?

Answer 19

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

Question 20

What are “Facultative aerobes”?

Answer 20

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

Question 21

What is nitrogen fixation?

Answer 21

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

Question 22

What domain contains most of the prokaryotes?

Answer 22

domain bacteria

Question 23

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

Answer 23

» 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”)

Question 24

What is Domain Archaea?

Answer 24

• 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 …)

Question 25

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

Answer 25

» 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

Question 26

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

Answer 26

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

Question 27

How do prokaryotes affect humans beneficially?

Answer 27

• 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

Question 28

How do prokaryotes affect humans negatively?

Answer 28

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

Question 29

How do humans use prokaryotes?

Answer 29

• 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