Archaea

What are archaea?

Archaea are microorganisms similar in size and genome to bacteria, often found in extreme environments.

What is the typical size range of archaeal cells?

Generally 0.5 to 5 μm in diameter, with some species like Thermoproteus spp. reaching up to 100 μm.

What shapes can archaeal cells take?

Archaeal cells can be rods, spheres, spirals, irregular, or rectangular.

Where do archaea typically live?

Archaea can live in extreme environments such as high temperatures, acidity, and salinity, as well as in typical conditions like temperate marine, freshwater, and soil.

What is an example of an archaeon that thrives in high salinity?

Halobacterium salinarum, which grows in 3.0 to 5.0 M NaCl.

What is an example of an archaeon that thrives at high temperatures?

Pyrococcus furiosus, which can survive at 100°C.

What is the significance of histones in archaea?

Histones may have been an early branch-point event in the evolution of archaea and eukarya, protecting DNA and allowing larger genomes.

How does archaeal DNA arrangement differ from bacteria?

Archaea have a nucleoid without a nuclear envelope and usually possess a single circular genome, with some using histones for DNA compaction.

How does transcription and translation in archaea compare to bacteria and eukaryotes?

Archaeal transcription and translation resemble eukaryotic processes, but can occur simultaneously like in bacteria.

What are the components of archaeal cytoplasm?

The cytoplasm contains similar components to bacteria, lacks membrane-enclosed organelles, and may have inclusion bodies.

What is a homolog in the context of archaea?

A homolog refers to a gene or protein that shares a common ancestry with a gene or protein in another organism.

What is the evolutionary relationship between archaea, bacteria, and eukaryotes?

Genetic analyses suggest that archaea and eukaryotes may have branched off from bacteria.

What role do inclusion bodies play in archaea?

Inclusion bodies serve as storage sites for nutrients or other substances within the archaeal cytoplasm.

What are the notable growth requirements for Picrophilus oshimae?

Picrophilus oshimae requires a pH of 0.7 and thrives in sulfur-rich volcanic regions.

What is the significance of the study by Woese and Fox in the 1970s?

They conducted studies that led to the classification of archaea as a separate domain based on rRNA gene comparisons.

What is the morphology of Sulfolobus spp.?

Sulfolobus spp. exhibit irregular shapes that are not typically found in bacteria.

What is the function of histones in archaea?

Histones protect DNA in high-temperature environments and facilitate the packaging of larger amounts of DNA.

What are the differences between archaeal and bacterial plasma membranes?

Archaeal plasma membranes have unique lipid compositions that differ from those of bacteria.

How do archaeal cell walls differ from those of bacteria?

Archaeal cell walls are composed of unique materials, such as pseudopeptidoglycan, unlike the peptidoglycan found in bacterial cell walls.

What is the significance of the archaeal cytoskeleton?

The archaeal cytoskeleton has homologues found in both bacteria and archaea, though it is less understood than in eukaryotes.

What are the characteristics of the archaeal nucleoid?

The archaeal nucleoid contains the genome and lacks a nuclear envelope, similar to bacteria.

What is the role of rRNA gene comparisons in understanding archaeal phylogeny?

rRNA gene comparisons help construct phylogenetic trees that clarify the evolutionary relationships among archaea, bacteria, and eukaryotes.

What is the typical habitat of Methanogenium frigidum?

Methanogenium frigidum is found in Ace Lake, Antarctica, and thrives at 15°C.

What is the evolutionary significance of the presence of histones in archaea?

The presence of histones may indicate a prerequisite for increased genome size and complexity, potentially leading to macroscopic life.

What does homology refer to in biology?

Homology refers to biological features, including genes and their products, that are descended from a feature present in a common ancestor.

What are homologous features in genetics called?

Homologs (or homologues in British spelling).

How do homologous genes become separated in evolution?

Through speciation (separation of two populations into different species) or gene duplication within a lineage.

What are genes called that are separated by speciation?

Orthologs.

What are genes called that are separated by gene duplication?

Paralogs.

What is an example of a homologous gene duplication event?

Gene 1 in the ancestral species duplicates to form Gene 1a and Gene 1b.

In the context of homologs, what is the relationship between Gene 1a in two different species?

Gene 1a in species one is the ortholog of Gene 1a in species two.

What are Gene 1a and Gene 1b considered in relation to each other?

They are paralogs.

What is a key characteristic of archaeal cytoplasm?

It has similar components to bacteria and lacks membrane-enclosed organelles.

What are cytoskeletal homologues found in Archaea?

Cytoskeletal homologues are proteins found in both Bacteria and Archaea.

What is the function of the archaeal plasma membrane?

It provides selective permeability, transport proteins, cell signaling, and secretion/uptake.

How does the archaeal plasma membrane differ from bacterial and eukaryotic membranes?

It has a different bilayer construction and can be a monolayer in some archaea.

What is the significance of isoprenoids in archaeal membranes?

Isoprenoids are the hydrophobic region in archaeal membranes, differing from fatty acids in bacteria.

What type of linkage is found in archaeal membranes?

Ether linkages, as opposed to ester linkages in bacterial and eukaryotic membranes.

What is pseudomurein?

A component of some archaeal cell walls, differing from peptidoglycan in structure.

What are the two types of cell wall structures found in Archaea?

Pseudomurein and other types depending on the species.

What is a common feature of archaeal cell surface structures?

Some archaeons use an S-layer for protection and adhesion.

What are cannulae in archaeons?

Hollow glycoprotein tubes that link cells together to form a complex network.

How do archaeal flagella differ from bacterial flagella?

Archaeal flagella are thinner, composed of different versions of flagellin, and likely grow from the base.

What are the four superphyla of Archaea?

Eurychaeota, TACK, DPANN, and Asgard.

What is a challenge in classifying Archaea?

Struggles with placing archaea into phylogenetic trees.

What adaptations do extremophiles in Archaea have?

They have strategies that allow them to function in extreme environments.

What is the two branch hypothesis in relation to Archaea?

Some scientists believe there are only two phylogenetic branches from which eukaryotes evolved.

What are the two well-defined phyla of Archaea?

Euryarchaeota and Crenarchaeota

What is the main challenge in placing archaea into phylogenetic trees?

The diversity within phyla and reliance on SSU rRNA sequencing.

What type of environments do methanogens thrive in?

Anoxic environments such as lake/ocean sediments, hot springs, and GI tracts.

What do halophiles require for survival?

NaCl concentration greater than 1.5M.

What are the salinity levels of the Great Salt Lake and the Dead Sea?

Great Salt Lake: 5-34% salinity; Dead Sea: 5-34% salinity.

How do halophiles resist osmotic shock?

By maintaining a high intracellular K+ concentration to offset high extracellular Na+ concentration.

What adaptations do Crenarchaeota have for survival in extreme conditions?

Tetraether lipids, more α-helical regions in proteins, and strong chaperone protein complexes.

What is the significance of high intracellular potassium levels in halophiles?

It can lead to protein denaturation and DNA splitting.

What are the four superphyla that archaeons can be classified into?

Euryarchaeota, TACK, DPANN, and Asgard.

What is a notable characteristic of Nanoarchaeota within the DPANN superphylum?

It has a small genome and forms distinct relationships with a host organism.

What recent discovery was made regarding Lokiarchaeota?

A proposed species was cultivated in 2020, linked to hydrothermal environments.

What do eukaryotic signature proteins (ESPs) indicate about Lokiarchaeum?

It may contain genes closely related to eukaryotes.

What is the proposed relationship between Eukarya and Asgard archaea?

Eukarya evolved from the Asgard superphylum.

What are the main groups within Euryarchaeota?

Methanogens and halophiles.

What environmental conditions do thermophiles prefer?

High temperatures, often above 55°C.

What are acidophiles and where do they thrive?

Organisms that thrive in low pH environments.

What adaptations do thermophiles have to survive high temperatures?

Thermostable DNA-binding proteins and reverse DNA gyrase for increased DNA supercoiling.

What is the role of strong chaperone protein complexes in extremophiles?

They help proteins maintain their structure under extreme conditions.

What is the significance of the 16s rRNA sequencing in archaea classification?

It helps in identifying and classifying the diverse groups within archaea.

What is the ecological role of methanogens?

They produce methane from substrates in anaerobic environments.

What challenges do halophiles face in high salt environments?

Osmotic shock due to water loss from the cell.

What are the typical salinity levels in the ocean?

Approximately 3.5% salinity (0.6 M).

What adaptations do halophiles have to deal with high salt concentrations?

Higher GC content in DNA and highly acidic proteins.

What is the significance of studying extremophiles like archaea?

They provide insights into the limits of life and potential biotechnological applications.

What does the term 'barophiles' refer to?

Organisms that thrive in high-pressure environments.

What are psychrophiles?

Organisms that thrive in cold temperatures.

Divergent Evolution

Species with a common ancestory evolve different traits to adapt to different environments, leading to speciation.

Convergent Evolution

Unrelated species from different ancestors independently evolve similar traits to adapt to similar environments.