Origins of Eukaryotic
Diversity - Protists
"Protists" is artificial grouping
- Evolutionary relationships have historically been unclear.
In past, were often classified by mode of nutrition: heterotrophs
by ingestion (called Protozoa) (Fig
28.1a) and amoeba,
the movie, heterotrophs by absorbtion (Fig
28.1c), and autotrophs through photosynthesis
(called algae) (Fig
28.1b and Fig
28.1d)and Euglena,
the movie. Recent DNA studies have determined some monophyletic
groups. (Fig
28.8)
Most are unicellular (Fig
28.3), some colonial, some multicellular. At cellular
level many are very complex.
EVOLUTION
OF EUKARYOTIC CELLS - A chimera of prokaryotic ancestors.
Origins of eukaryotes - Endosymbiotic
theory. (Fig
28.4). And 2 more. (OH1 and OH2). See a slide show here.
- cells with membrane-bound organelles
newest evidence from Australia indicates they originated 2.7
billion years ago
Autogenous event
- - Nuclear membrane
- - endoplasmic reticulum
Endosymbiotic event - serial endosymbiosis
- - Mitochondria
- - Chloroplasts
Evidence for the endosymbiont theory is that mitochondria and
chloroplasts:
- - Are appropriate size to be descendants of eubacteria.
- - Have inner membranes similar to those on prokaryotic plasma
membranes.
- - Replicate by splitting, as in prokaryotes.
- - DNA is circular and different from the DNA of the cell's
nucleus.
- - Contain their own components for DNA transcription and
translation into proteins .
- - Have ribosomes similar to prokaryotic ribosomes.
- - Molecular systematics lend evidence to support this theory.
- - Many extant organisms are involved in endosymbiotic relationships.
Protists are eukaryotic organisms having:
- - true nuclei (Fig.
7.9)
- - membrane-enclosed organelles (Figs. 7.7
and 7.8)
- - "9+2" flagella and cilia. Most have flagella
or cilia (Figs 7.24
and 7.23).
See cilia
on Vorticella, the movie. Cilia,
the movie!
Many protists are parasites of humans:
- Giardia (Fig
28.9)
- Trichomonas vaginalis (Fig
28.10)
- Trypanosoma spp. cause sleeping sickness (Fig
28.11)
- Plasmodium spp. cause malaria (Fig
28.13)
Table
28.1 provides a summary of the Kingdoms of protists, but does
NOT cover ALL the protists. You are NOT responsible for learning
the various groups.