lecture 2 Flashcards
microbial evolution and diversity
what are the 2 hypothesises for the evolution of cellular life?
Surface origin hypothesis
Darwin thought life evolved from a ‘warm little ponds’ (primordial soup theory) on the anaerobic earth (at the time), where organic molecules formed spontaneously from chemical reactions from high uv, meteor strikes and volcanic activity.
There was no ozone (ozone protects planet from high uv) and the surface was violent and constantly being ruptured.
SO life can’t have started on the surface because it’s not easy.
Subsurface origin hypothesis
Earth cooled down enough for water to precipitate out into the atmosphere and sit in ocean basins. The earth had a lot of volcanic activities so the ocean basins had hydrothermal vents where gases and compounds from the inside of the planet come out through those hydrothermal vents. Because they’re surrounded by water, they’re more stable than they are on the surface, and they have a constant source of energy from the reduced inorganic compounds.
explain the surface origin hypothesis
Darwin thought life evolved from a ‘warm little ponds’ (primordial soup theory) on the anaerobic earth (at the time), where organic molecules formed spontaneously from chemical reactions from high uv, meteor strikes and volcanic activity.
There was no ozone (ozone protects planet from high uv) and the surface was violent and constantly being ruptured.
SO life can’t have started on the surface because it’s not easy.
explain the subsurface origin hypothesis
Earth cooled down enough for water to precipitate out into the atmosphere and sit in ocean basins. The earth had a lot of volcanic activities so the ocean basins had hydrothermal vents where gases and compounds from the inside of the planet come out through those hydrothermal vents. Because they’re surrounded by water, they’re more stable than they are on the surface, and they have a constant source of energy from the reduced inorganic compounds.
Much more stable so it’s more likely for life to have started here.
These ecosystems are entirely detached from sunlight and use energy from the ocean crust only (inorganic compounds in it).
what are the key features of cellular life? (6)
• Self replicating RNA (RNA world, ribozymes) • Enzymatic proteins • DNA - genetic code • Evolution of biochemical pathways • Divergence of lipid biosynthesis • Divergence of cell walls
(more info in L2 word doc)
what is the last universal common ancestor
The last universal common ancestor is a proto organism (not bacteria or archaea) from which came the archaeal and bacterial lineage. (lineage - evolution).
explain the landmarks in the biological evolution (4)
• Early life probably dependent on H2 and CO2 (bacteria making acetate, archaea making methane) • Energy and carbon metabolisms diversify • Phototrophy, using H2S as electron donor • Evolved into a oxygenic photosystem using H2O (oxygenation of atmosphere, life alters the whole geosphere)
more info in L2 word doc
discovering archaea and bacteria
Before molecular biology, we didn’t know there were 2 types of prokaryotes (bacteria and archaea). Discovering archaea allowed us to determine how related organisms are to each other.
(archaea are as different to bacteria, as bacteria are to eukaryotes)
method of generating a phylogenetic tree
isolate the DNA, sequence the DNA using PCR, align the sequence against other organisms to see the differences (more differences in a sequence - further apart)
marker molecules in diversity studies
Certain molecular sequences are useful in phylogenetic analysis.
Conditions:
- they must be universal
- contain variable and conserved regions
- not be subject to horizontal gene transfer (if a gene is transferred all the time, it won’t carry a signal of what its history is, it’s gonna carry a signal of where it’s been)
- be truly homologous (must perform the same function in a cell)
for example, ribosomal RNA genes are a universal molecular marker (present in all species and even in LUCA)
other examples: ATPase subunits, EF-Tu, RecA
what are the 2 potential chain of events for the evolution of eukaryotes?
ancestor of mitochondrion
nucleus formed
ancestor of chloroplasts
splits into animals and plants in the eukarya domain
nucleus formed
ancestor of mitochondrion
ancestor of chloroplasts
splits into animals and plants in the eukarya domain
what are the 2 hypothesises of the eukaryotic evolution?
• Endosymbiont theory:
Mitochondria: Incorporation of aerobic chemo-organotrophic
bacteria into a host (bacterial?) cell
Chloroplasts: Incorporation of phototrophic cyanobacteria
into a eukaryotic cell
• Hydrogen hypothesis:
Association of an archaeal host using H2 as energy source with
an aerobic bacterium that produced hydrogen as a ‘waste’
product
explain the organisms we have no cultured relative member of
We detected them by getting water or soil, use PCR to amplify the genes we know carry phylogenetic signals and we find that they have a sequence that has no resemblance to anything we’ve found before.
examples of organisms we do know some things about (8)
Aquifex - hyperthermophile, chemolithoautotroph (oxidises H2 to water using O2 as an e- acceptor)
Deinococcus - extremely radiation resistant, very rapidly reassembles DNA that was damaged by radiation in 15min
Cyanobacteria & plastids - plastids (chloroplasts in plants) were originally cyanobacteria, morphologically diverse, oxygenic phototrophs, have different colours because they have different pigment that capture different energies of light
Actinobacteria - high GC gram positives, heterotrophs, include pathogens (leprosy, tb, diptheria)
Firmicutes - low G+C positives, heterotrophs mostly, medically important, used in food processing
Chlamidya - obligate intracellular parasites
Spirochaetes - intracellular, human pathogens like lyme diseases and syphillis
Proteobacteria - metabollically diverse, many pathogens
define anoxygenic
photosynthesis without oxygen - using H2S hydrogen sulfide as an e- donor ( produces sulfur as a waste product
define cyanobacterial cell
prokaryotic microorganisms that are related to the bacteria but are capable of photosynthesis
