eukaryotes

Examples of eukaryotes in the following topics:

• Shared Features of Archaea and Eukaryotes

  • Archaea possess genes and several metabolic pathways that are more closely related to those of eukaryotes than prokaryotes.
  • The evolutionary relationship between archaea and eukaryotes remains unclear.
  • The leading hypothesis is that the ancestor of the eukaryotes diverged early from the Archaea, and that eukaryotes arose through fusion of an archaean and eubacterium, which became the nucleus and cytoplasm.
  • The chromosomes replicate from multiple starting-points (origins of replication) using DNA polymerases that resemble the equivalent eukaryotic enzymes.
  • Eukaryotes are colored red, archaea green and bacteria blue.

• Phylogeny of the Eukarya

  • Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota.
  • All large complex organisms are eukaryotes, including animals, plants, and fungi.
  • Eukaryotes are split into 6, subdivisions, referred to as kingdoms .
  • It has been estimated that there may be 75 distinct lineages of eukaryotes.
  • This is one hypothesis of eukaryotic relationships.

• Historical Overview of Eukaryotes

  • Until more recent work, the historical view of eukaryotes has been anthropomorphic.
  • The various single-cell eukaryotes were originally placed with plants or animals when they became known.
  • This group was expanded until it encompassed all single-cell eukaryotes.
  • The eukaryotes came to be composed of four kingdoms: Kingdom Protista, Kingdom Plantae, Kingdom Fungi, and Kingdom Animalia.
  • The disentanglement of the deep splits in the tree of life only really got going with DNA sequencing, leading to a system of domains rather than kingdoms as top level rank being put forward by Carl Woese, uniting all the eukaryote kingdoms under the eukaryote domain .

• Control of Transcription in Archaea

  • Transcription and translation in archaea resemble these processes in eukaryotes more than in bacteria.
  • Archaea are genetically distinct from bacteria and eukaryotes, with up to 15% of the proteins encoded by any one archaeal genome being unique to the domain, even though most of these unique genes have no known function.
  • The proteins that archaea, bacteria and eukaryotes share form a common core of cell function, relating mostly to transcription, translation, and nucleotide metabolism.
  • Transcription and translation in archaea resemble these processes in eukaryotes more than in bacteria, with the archaean RNA polymerase and ribosomes being very close to their equivalents in eukaryotes.
  • Compare the archaea with bacteria and eukaryotes in terms of their general mechanisms of gene expression

• Newly Discovered Eukaryotes

  • There are many new species to be discovered, including eukaryotic species.
  • Considering how large an elephant is, this should point out how little we know about the numbers of microscopic eukaryotes that are yet to be discovered.
  • Of course we may never truly identify many eukaryotic species, since the rate of extinction has increased.
  • This does not include many microscopic eukaryotic groups.

• Archaeal Gene Regulation

  • Archaea are genetically distinct from bacteria and eukaryotes, with up to 15% of the proteins encoded by any one archaeal genome being unique to the domain, although most of these unique genes have no known function.
  • The proteins that archaea, bacteria, and eukaryotes share form a common core of cell function, relating mostly to transcription, translation, and nucleotide metabolism.
  • Transcription and translation in archaea resemble these processes in eukaryotes more than in bacteria, with the archaean RNA polymerase and ribosomes being very close to their equivalents in eukaryotes.
  • Although archaea only have one type of RNA polymerase, its structure and function in transcription seems to be close to that of the eukaryotic RNA polymerase II, with similar protein assemblies (the general transcription factors) directing the binding of the RNA polymerase to a gene's promoter.
  • Post-transcriptional modification is simpler than in eukaryotes, since most archaean genes lack introns, although there are many introns in their transfer RNA and ribosomal RNA genes, and introns may occur in a few protein-encoding genes.

• Opisthokonts: Animals and Fungi

  • The opisthokonts, or "fungi/metazoa group", are a broad group of eukaryotes, including both the animal and fungus kingdoms, together with the eukaryotic microorganisms that are sometimes grouped in the paraphyletic phylum choanozoa (previously assigned to the protist "kingdom").
  • In contrast, flagellate cells in other eukaryote groups propel themselves with one or more anterior flagellae.
  • Cavalier-Smith and Stechmann argue that the uniciliate eukaryotes such as opisthokonts and Amoebozoa, collectively called unikonts, split off from the other biciliate eukaryotes, called bikonts, shortly after they evolved.

• Ribosomes

  • In eukaryotes, ribosomes can commonly be found in the cytosol of a cell, the endoplasmic reticulum or mRNA, as well as the matrix of the mitochondria.
  • This protein-synthesizing organelle is the only organelle found in both prokaryotes and eukaryotes, asserting the fact that the ribosome is a trait that evolved early on, most likely present in the common ancestor of eukaryotes and prokaryotes.
  • All prokaryotes have 70S (where S=Svedberg units) ribosomes while eukaryotes contain larger 80S ribosomes in their cytosol.
  • These rRNA molecules differ in size in eukaryotes and are complexed with a large number of ribosomal proteins, the number and type of which can vary slightly between organisms.
  • Compare and contrast ribosome structure and function in prokaryotes and eukaryotes

• The Taxonomic Scheme

  • In the currently accepted scientific classification of Life, there are three domains of microorganisms: the Eukaryotes, Bacteria and Archaea, The different disciplines of study refer to them using differing terms to speak of aspects of these domains, however, though they follow similar principles.
  • In the Molecular era of classification, Carl Woese, who is regarded as the forerunner of the molecular phylogeny revolution, argued that the bacteria, archaea, and eukaryotes represent separate lines of descent that diverged early on from an ancestral colony of organisms.
  • Since the Archaea and Bacteria are no more related to each other than they are to eukaryotes, the term prokaryote's only surviving meaning is "not a eukaryote", limiting its value.
  • Thus, though Woese identified three primary lines of descent the Archaebacteria, the Eubacteria and the Urkaryotes, the latter now represented by the nucleocytoplasmic component of the Eukaryotes. these lineages were formalised into the rank Domain (regio in Latin) which divided Life into 3 domains: the Eukaryota, the Archaea and the Bacteria.
  • Eukaryotes are colored red, archaea green and bacteria blue.

• Chromosomes and DNA Replication in the Archaea

  • This process in Archaea appears to be similar to both bacterial and eukaryotic systems.
  • The circular chromosomes contain multiple origins of replication, using DNA polymerases that resemble eukaryotic enzymes.
  • The primase used to synthesize a short RNA primer from the free 3'OH group varies in Archaea when compared to that of bacterial and eukaryotic systems.
  • Once the RNA primase has performed its job, DNA synthesis continues in a similar fashion by which the eukaryotic system and the DNA is replicated.