General introduction to prokaryotes
Biodiversity = the variation of taxonomic life forms within a given
ecosystem, biome or for the entire Earth.
Biodiversity is often a measure of health of biological system – the
greater the biodiversity the healthier the system
Rainforests are among the most biodiverse ecosystems on Earth
Bacterial biodiversity:
Bacteria – underpin all of the biogeochemical cycles – probably as
consortia (interconnected webs)
Prokaryotic cells: small, ubiquitous, diverse, persistent (robust,
adaptive, numerous), characterised by absence of a nuclear
membrane
History & taxonomy
- first bacteria observed by Antony van Leeuenhoek in 1683 using a
single-lens microscope of his own design.
- The name bacterium was introduced much later, by Ehrenberg in
1828, derived from the Greek word meaning “small stick”
- Louis Pasteur (1822-1895) and Robert Koch (1843-1910) described
the role of bacteria as conveyers and causes of disease/ pathogens.
Louis Pasteur:
- Championed changes in hospital practises to minimise the spread
of disease by microbes
- He discovered that weakened forms of a microbe could be used as
an immunisation against more virulent forms of the microbe
- Found that rabies was transmitted by agents so small they couldn’t
be seen under a microscope, thus revealing the world of viruses
- Also developed “pasteurisation”, a process by which harmful
microbes in perishable food products are destroyed using heat,
without destroying the food
Prokaryotic features and consequences
Prokaryotic Eukaryotic
Mostly small (1-10µm) and simple Mostly large (10-100µm) and complex
No membrane bound organelles, Complex compartmentalised
no microtubules, no mitochondria interior
Direct cell division by binary Mitotic cell division
fission
Very metabolically diverse and Aerobic respiration,
tolerant of extreme conditions photosynthesis and fermentation
only
70S Ribosomes 80S Ribosomes
Single chromosome without a Many linear chromosomes
nuclear membrane enclosed in a nuclear membrane
No sexual reproduction Sexual reproduction dominant
, Sex common Sex common
Binary fission: an efficient growth method
Metabolically diverse and tolerant: e.g. high temperature, low
pH, narrow temperature range, iron as an energy source, high
pressure, hydrogen sulphide as a toxic energy source
70S Ribosome – 3 RNA subunits & protein. The division of the
Tree of Life into 3 domains (Bacteria, Archaea, Eucaraya) is based
almost entirely on sequence comparison of ribosomal RNA.
Foundation of modern bacteriology.
No nuclear membrane: ribosomes can approach the DNA and
attach directly to the mRNA transcript – simultaneous transcription
and translation.
No sexual reproduction:
- Single, usually circular, genome
- Highly supercoiled
- Obligate haploid
- Most genes are single copy not allelic
- All mutations are visible
- Often small circular elements called plasmids
- Sexually isolated – species problems
But sex is quite common: sex via conjugation
- Unidirectional transfer of fragments of DNA
- Various mechanisms
- Substantial proportion of a species’ genetic information may be
derived from sex
Biodiversity = the variation of taxonomic life forms within a given
ecosystem, biome or for the entire Earth.
Biodiversity is often a measure of health of biological system – the
greater the biodiversity the healthier the system
Rainforests are among the most biodiverse ecosystems on Earth
Bacterial biodiversity:
Bacteria – underpin all of the biogeochemical cycles – probably as
consortia (interconnected webs)
Prokaryotic cells: small, ubiquitous, diverse, persistent (robust,
adaptive, numerous), characterised by absence of a nuclear
membrane
History & taxonomy
- first bacteria observed by Antony van Leeuenhoek in 1683 using a
single-lens microscope of his own design.
- The name bacterium was introduced much later, by Ehrenberg in
1828, derived from the Greek word meaning “small stick”
- Louis Pasteur (1822-1895) and Robert Koch (1843-1910) described
the role of bacteria as conveyers and causes of disease/ pathogens.
Louis Pasteur:
- Championed changes in hospital practises to minimise the spread
of disease by microbes
- He discovered that weakened forms of a microbe could be used as
an immunisation against more virulent forms of the microbe
- Found that rabies was transmitted by agents so small they couldn’t
be seen under a microscope, thus revealing the world of viruses
- Also developed “pasteurisation”, a process by which harmful
microbes in perishable food products are destroyed using heat,
without destroying the food
Prokaryotic features and consequences
Prokaryotic Eukaryotic
Mostly small (1-10µm) and simple Mostly large (10-100µm) and complex
No membrane bound organelles, Complex compartmentalised
no microtubules, no mitochondria interior
Direct cell division by binary Mitotic cell division
fission
Very metabolically diverse and Aerobic respiration,
tolerant of extreme conditions photosynthesis and fermentation
only
70S Ribosomes 80S Ribosomes
Single chromosome without a Many linear chromosomes
nuclear membrane enclosed in a nuclear membrane
No sexual reproduction Sexual reproduction dominant
, Sex common Sex common
Binary fission: an efficient growth method
Metabolically diverse and tolerant: e.g. high temperature, low
pH, narrow temperature range, iron as an energy source, high
pressure, hydrogen sulphide as a toxic energy source
70S Ribosome – 3 RNA subunits & protein. The division of the
Tree of Life into 3 domains (Bacteria, Archaea, Eucaraya) is based
almost entirely on sequence comparison of ribosomal RNA.
Foundation of modern bacteriology.
No nuclear membrane: ribosomes can approach the DNA and
attach directly to the mRNA transcript – simultaneous transcription
and translation.
No sexual reproduction:
- Single, usually circular, genome
- Highly supercoiled
- Obligate haploid
- Most genes are single copy not allelic
- All mutations are visible
- Often small circular elements called plasmids
- Sexually isolated – species problems
But sex is quite common: sex via conjugation
- Unidirectional transfer of fragments of DNA
- Various mechanisms
- Substantial proportion of a species’ genetic information may be
derived from sex
