THE PROTISTS

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THE PROTISTS
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The dilemma

• Systematists have split protists into many
  kingdoms.
• Originally grouped as mostly unicellular
  eukaryotes
• Problem Paraphyletic grouping
• Now used as an informal term

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Great Diversity

• Unicellular, multicellular colonial
• Heterotrophs, autotrophs, mixotrophs
• Euglena
• Nutrition is not a reliable taxonomic
  characteristic
• Three categories
• Protozoa animal-like
• Slime Molds fungus like
• Algae plant-like

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Euglena Where does it belong?
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Motility

• Cilia Flagella
• Not homologous to those of prokaryotes
• Extensions of cytoskeleton

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Reproduction

• Haploid stage is main stage of most protists
• Modes of reproduction
• Asexual
• Exchange gametes (2n), reproduce asexually
• Conjugation

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Ecological Importance

• Found anywhere there is water
• Creep through damp sand and silt
• Attach to submerged rocks
• Drifting plankton
• Phytoplankton are the bases of aquatic food
  chains
• Algal blooms red tide
• Symbionts
• Mutualism
• Trichonympha
• Parasitic
• Plasmodium

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Origin of Eukaryotes

• Prokaryotes are limited in the number of
  different metabolic activities
• Small size limits the number of genes
• Trends in evolution
• Multicellular
• Build communities
• Compartmentalization

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Endosymbiosis

• Organelles were formerly prokaryotes
• Led to mitochondria and plastids
• Entered as undigested prey or parasite
• Mutualism

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Endosymbiosis

• Evidence
• Organelles show similarities with bacteria
• Size
• Enzymes and transport systems in the inner
  membrane
• Binary fission
• Single circular DNA RNA
• Mitochondria lacks histones like prokaryotes
• Ribosomes resemble those of bacteria

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The Chimera

• Made up of prokaryote parts
• Closest living prokaryotic relative?
• rRNA analysis
• Mitochondria proteobacteria
• Plastids cyanobacteria
• Not genetically self-sufficient
• Genes for some of its proteins are in cells
  nucleus
• Proteins in the organelle are chimera of
  polypeptides encoded in organelle nucleus DNA
• Hypothesis endosymbionts transferred DNA to
  host genome (transformation)

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Secondary Endosymbiosis

• Plastids are scattered throughout phylogenetic
  tree of eukaryotes
• Differ in the number of membranes
• Plastids were acquired independently several
  times during the early evolution of eukaryotes
• Two waves
• Primary endosymbiont cyanobacteria
• Secondary endosymbiont algae containing
  plastids
• Evidence
• Cryptomonad algae plastids contain remnants of
  nucleus, and ribosomes

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Secondary Endosymbiosis
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Webof Life

• Eukaryotes evolved by a fusion of species from
  separate phylogenetic lineages.
• Primitive cells of the ancestral community
  swapped DNA
• Replace tree with a web-like phylogeny?

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Back to the Kingdom Problem(?)