Protists Origin of eukaryotic cells Read all of chapter 27, but don’t concentrate on memorizing all names. Focus on major evolutionary trends, and the names that are emphasized in the lectures.

The protists Simple, mostly unicellular, eukaryotes. Once called the kingdom Protista. Now regarded as a very diverse group, that is not monophyletic when viewed as a whole. Classification poorly understood, probably will be regarded as 4 or more small kingdoms. Photosynthetic protists often called “algae” Animal-like protists called “protozoa”

Origin of eukaryotic cells Early prokaryotic cell, from the archaean lineage, developed an amoeboid life form (flexible outline and pseudopodia; feeding by engulfing prey). Endomembrane system and nuclear envelope evolved from in-foldings of the plasmamembrane. Mitochondria and chloroplasts were acquired by engulfing bacteria, which continued to live inside the surrounding cells in an endosymbiotic relationship.

Evidence for the endosybiotic hypothesis Mitochondria and chloroplasts have their own DNA; it is naked and circular Mitochondria and chloroplasts have their own ribosomes; they are 70S like bacteria. Endosymbiosis explains the double membrane around mitochondria, and the double, triple, or quadruple membranes around various chloroplasts.

Mitochondria and chloroplasts have evolved from bacteria… … but they are not bacteria any more. Through billions of years of evolution they have lost the ability to live independently. The organelle genome is incomplete; some genes needed for mitochondrial or chloroplast function have been transferred to the cell nucleus.

Euglenozoa Unicellular, flexible body, anterior flagella. Some are photosynthetic by secondary endosymbiosis. All are capable of heterotrophic feeding. Photosynthetic Euglena Pathogenic species like trypanosomes sleeping sickness, leishmaniasis, Chagas disease

Alveolata Dinoflagellates (red tide algae) Apicomplexans (malaria parasite Plasmodium) Ciliates (many short flagella, e.g. Paramecium)

Stramenopila Diatoms – unicellular algae with glassy walls Brown algae – multicellular seaweeds, often very large (kelp, sargassum, etc.) Photosynthetic pigments include chlorophyll a, chlorophyll c, and fucoxanthins. Water molds and powdery mildews – Heterotrophs similar to fungi (but with flagellated reproductive cells which true fungi lack). Includes several plant diseases such as the Irish potato blight.

Rhodophyta – red algae Unicellular algae or multicellular seaweeds. Most live in deep waters. Possess chlorophyll a, but not b or c. Unique red pigments phycoerythrin and phycocyanin allow them to absorb greenish light (accessory photosynthetic pigments)

Chlorophyta – the green algae Traditionally considered as protists because they are simpler than other plants. However it is now becoming clear that they are very closely related to plants and cannot be considered monophyletic on their own. Identical photosynthetic pigments to plants: chlorophyll a, chlorophyll b, carotenes. Simple alternation of generations.

Skim pages 496-498 but don’t worry about details.