Prokaryotes: Bacteria and Archaea Flashcards
Evolution of Life Over Geologic Time
The history of life is a story of DIVERSIFICATION - the rapid increase of new taxa and extinction. There are 4 eons of geologic time:
1. Hadean
2. Archaean
3. Proterozoic
4. Phanerozoic
Hadean Eon
- 4.6-4.0 BYA
- occurred before life arose
- before compelling evidence of life
Archaean Eon
- 4.0-2.5 BYA
- featured the evolution of early life including bacteria, archaea, and the first CYANOBACTERIA capable of oxygenic photosynthesis
Proterozoic Eon
- 2.5 BYA-542 MYA
- featured oxygen accumulation (the Oxygen Revolution)
- first single-celled and multicellular eukaryotes
- flourishing of early microbial and multicellular life
Phanerozoic Eon
- 542 MYA-Present
- beginning with the Cambrian explosion
- features the increase of plant and animal life
Three Domains of Life
- all share a single common ancestor
- fossils indicates prokaryotes (A + B) were the first living organisms
Bacteria Unique Traits
- Bacterial cell walls are composed of peptidoglycan, a protein and sugar complex
Archaea Unique Traits
- Archaeal cell walls are composed of polysaccharides (sugar)
- Archaeal membranes contain branched isoprene chains
Eukarya Unique Traits
- DNA in nucleus
- unicellular and multicellular
- membrane bound organelles
- multiple linear chromosomes
- reproduce through mitosis
- plant cells walls (cellulose) and fungi cell walls (chitin)
Earliest Life on Earth
Evidence suggests life arose during the ARCHEAN:
- Microfossils
- Biosignatures
- Stromatolites
Earliest Life on Earth: Microfossils
suggest life arose between 3.5-3.8 BYA
Earliest Life on Earth: Biosignatures
suggests life may have been present as early as 4.1 BYA
- include chemical isotopes/molecules that suggest biological activity life specific carbon isotopes and components of FA, proteins, and nucleic acids
- First living things were single-celled prokaryotic anaerobes and likely chemotrophic
Earliest Life on Earth: Stromatolites
layered sedimentary structures produced by microbes as they create a series pf multi-layered sheets composed of successive generations of microorganisms
- Date 3.48-3.7 BYA
- Might have included photosynthetic bacteria (though not oxygenic yet)
The Oxygen Revolution
the evolution of oxygenic photosynthesis of early cyanobacteria that began near end-Archean (2.6 BYA)
- Cyanobacteria split water to produce oxygen byproduct, generating the first free molecular O2 in early Earth’s atmosphere
- Free O2 reacted with soluble iron in the oceans, causing iron oxide to precipitate
- Oceans were not fully oxygenated until 850 MYA near the end-Proterozoic
- Evidence of SLOW ACCUMULATION of O2 is BANDED IRON FORMATIONS in sedimentary rocks
Origin of Eukaryotes
Microfossil evidence suggests that eukaryotes arose between 1.6-2.2 BYA during the Proterozoic after the start of the Oxygen Revolution
First Multicellular Life
- Much of life on Earth was single-celled until end-Proterozoic
- Multicellular life appeared in the fossil record ~600 MYA near end-Proterozoic
The Cambrian Explosion
adaptive radiation that includes the emergence of nearly all modern animal phyla (~542 MYA)
- spans millions of years
- the accumulation of oxygen from the Oxygen Revolution most likely caused this
- oxygen could support the evolution of larger organisms and high metabolic rates
- led to the extinction of anaerobic organisms
The Cambrian Explosion: THE SHIFT
An anoxic environment populated by anaerobic, single-celled prokaryotes
—>
Eukaryotes living in micro-aerophilic environments
—>
Multicellular organisms in an oxygen-rich environment
Phylogenetic Relationships: B.A.E.
- Archaea and Bacteria are both prokaryotes but they do NOT form a monophyletic group in the tree of life
- Archaea and Eukarya form a monophyletic group
- All have DNA, are living, and evolve
Traits Shared by Bacteria and Archaea
- unicellular
- prokaryotes
- lack membrane-bound organelles
- single circular chromosome in the nucleoid
- reproduce asexually (binary fission)
- Cannot reproduce sexually
- Horizontal Gene Transfer
Horizontal Gene Transfer
sharing genetic information between cells, resulting in shared DNA between individuals maybe not genetically related
- primary way antibiotic resistance spreads
- causes problems when identifying evolutionary relationships as the presence of a gene in different microbial species may not indicate homology by HGT
Photoautotroph
obtain energy from sunlight and carbon from CO2
Chemoheterotrophs
obtain energy and carbon from an organic chemical source
Chemoautotrophs
obtain energy from inorganic compounds and build their complex molecules from CO2
Photoheterotrophs
obtain energy from sunlight but require an organic carbon source (they cannot reduce CO2 into organic carbon
Metabolic Diversity
- Prokaryotes: Photoautotrophs, Chemoheterotrophs, Chemoautotrophs, Photoheterotrophs
- Eukaryotes: photoautotrophs (plants and some protists) OR chemoheterotrophs (animals, fungi, and some protists)
