Prokaryotes: Bacteria and Archaea

Question 1

Evolution of Life Over Geologic Time

Answer 1

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

Question 2

Hadean Eon

Answer 2

• 4.6-4.0 BYA
• occurred before life arose
• before compelling evidence of life

Question 3

Archaean Eon

Answer 3

• 4.0-2.5 BYA
• featured the evolution of early life including bacteria, archaea, and the first CYANOBACTERIA capable of oxygenic photosynthesis

Question 4

Proterozoic Eon

Answer 4

• 2.5 BYA-542 MYA
• featured oxygen accumulation (the Oxygen Revolution)
• first single-celled and multicellular eukaryotes
• flourishing of early microbial and multicellular life

Question 5

Phanerozoic Eon

Answer 5

• 542 MYA-Present
• beginning with the Cambrian explosion
• features the increase of plant and animal life

Question 6

Three Domains of Life

Answer 6

• all share a single common ancestor
• fossils indicates prokaryotes (A + B) were the first living organisms

Question 7

Bacteria Unique Traits

Answer 7

• Bacterial cell walls are composed of peptidoglycan, a protein and sugar complex

Question 8

Archaea Unique Traits

Answer 8

• Archaeal cell walls are composed of polysaccharides (sugar)
• Archaeal membranes contain branched isoprene chains

Question 9

Eukarya Unique Traits

Answer 9

• DNA in nucleus
• unicellular and multicellular
• membrane bound organelles
• multiple linear chromosomes
• reproduce through mitosis
• plant cells walls (cellulose) and fungi cell walls (chitin)

Question 10

Earliest Life on Earth

Answer 10

Evidence suggests life arose during the ARCHEAN:
- Microfossils
- Biosignatures
- Stromatolites

Question 11

Earliest Life on Earth: Microfossils

Answer 11

suggest life arose between 3.5-3.8 BYA

Question 12

Earliest Life on Earth: Biosignatures

Answer 12

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

Question 13

Earliest Life on Earth: Stromatolites

Answer 13

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)

Question 14

The Oxygen Revolution

Answer 14

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

Question 15

Origin of Eukaryotes

Answer 15

Microfossil evidence suggests that eukaryotes arose between 1.6-2.2 BYA during the Proterozoic after the start of the Oxygen Revolution

Question 16

First Multicellular Life

Answer 16

• Much of life on Earth was single-celled until end-Proterozoic
• Multicellular life appeared in the fossil record ~600 MYA near end-Proterozoic

Question 17

The Cambrian Explosion

Answer 17

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

Question 18

The Cambrian Explosion: THE SHIFT

Answer 18

An anoxic environment populated by anaerobic, single-celled prokaryotes
—>
Eukaryotes living in micro-aerophilic environments
—>
Multicellular organisms in an oxygen-rich environment

Question 19

Phylogenetic Relationships: B.A.E.

Answer 19

• 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

Question 20

Traits Shared by Bacteria and Archaea

Answer 20

• unicellular
• prokaryotes
• lack membrane-bound organelles
• single circular chromosome in the nucleoid
• reproduce asexually (binary fission)
• Cannot reproduce sexually
• Horizontal Gene Transfer

Question 21

Horizontal Gene Transfer

Answer 21

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

Question 22

Photoautotroph

Answer 22

obtain energy from sunlight and carbon from CO2

Question 23

Chemoheterotrophs

Answer 23

obtain energy and carbon from an organic chemical source

Question 24

Chemoautotrophs

Answer 24

obtain energy from inorganic compounds and build their complex molecules from CO2

Question 25

Photoheterotrophs

Answer 25

obtain energy from sunlight but require an organic carbon source (they cannot reduce CO2 into organic carbon

Question 26

Metabolic Diversity

Answer 26

• Prokaryotes: Photoautotrophs, Chemoheterotrophs, Chemoautotrophs, Photoheterotrophs
• Eukaryotes: photoautotrophs (plants and some protists) OR chemoheterotrophs (animals, fungi, and some protists)