Chap 28

• Eukaryotic cells differ from prokaryotes

  1. Presence of a cytoskeleton.
  2. Compartmentalization (nucleus and organelles)..
• Many organelles evolved via endosymbiosis between an ancestral eukaryote and a bacterial cell.
• Endosymbiosis supported by

  1. DNA inside mitochondria and chloroplasts.

  2. Ribosomes inside mitochondria similar to bacterial ribosomes.

  3.Chloroplasts and mitochondria replicate by binary fission – not mitosis.
• Prokaryotes carry genes on single DNA molecule while Eukaryotes have multiple chromosomes
• Protists are the most diverse of the four eukaryotic kingdoms.

  They exist considerably in every other aspect, Unicellular, colonial, and multicellular groups, Most are microscopic but some are huge, All symmetries and All types of nutrition.
• All of the eukaryotic subgroups are Excavata, Chromalveolata, Archaeplastida, Rhizaria, Amoebozoa and Ophisthokonta.
• Protists are Paraphyletic. Protists are present in all six eukaryotic supergroups.
• Cell surface in protists Protists have varied array of cell surfaces

  1. Plasma membrane
  2. Extracellular matrix (ECM) in some.
  3. Cysts - Dormant cell with resistant outer covering(Used for disease transmission)
• Locomotion in protists

  
  

  - Flagella One or more

  - Cilia • Shorter and more numerous than flagella.

  - Pseudopodia (“false feet”) •
• Nutrition in protists

  Autotrophs - Some photosynthetic or chemoautotrophic.

  Heterotrophs - Phagotrophs Ingest particulate food matter.

  Mixotrophs are both phototrophic and heterotrophic
• Reproduction in protists Asexual reproduction is the typical mode of reproduction.
• Some species have an unusual mitosis.

  • Mitosis – equal size daughter cells.

  • Budding – one daughter cell smaller.

  • Schizogony – cell division preceded by several nuclear divisions; produces several individuals.
• Excavata group consists of diplomonads, parabasalids, and euglenozoans.
• Excavata Groups

  Diplomonads - Unicellular, multiple flagella 2 nuclei Giardia - parasite Lack functional mitochondria

  Parabasalids - Some live in termite guts, STD Undulating membrane for locomotion, Use flagella, Have semifunctional mitochondria.

  Euglenozoa - hange shape when swimming between being stretched out and rounded up, lack cell walls, earliest eukaryotes to possess mitochondria Include free-living euglenids and parasitic kinetoplastids.
• Parasitic kinetoplastids - 2nd major group in Euglenozoa Unique and single mitochondrion.

  Difficult to control because organisms repeatedly change their protective coat.
• Chromalveolates Supergroup consisting of two branches: the alveolates and the stramenopiles.
• Alveolates are a subgroup of Chromalveolates. The Alveolates subgroups contain Dinoflagellates, Apicomplexans and Ciliates.
• Dinoflagellates- Photosynthetic, unicellular with flagella, live in aquatic areas, not complex with histones. Asexual, cause of red tide. Animals can die from exposure.
• Apicomplexans - Spore-forming animal parasites, Apical complex is a unique shape of organelles at one end of the cell (Enables the cell to invade its host) Plasmodium causes malaria • Complex life cycle – sexual, asexual, different hosts.
• Ciliates Feature large numbers of cilia arranged in longitudinal rows or spirals around the cell

  • Pellicle – tough but flexible outer covering
  • 2 types of nuclei

  Micronucleus – used only as germ line for sexual reproduction; DNA not transcribed

  Macronucleus – essential for function.

  • Have two types of vacuoles
  • Food vacuoles – digestion of food.
  • Contractile vacuoles – regulation of water balance.
• Stramenopiles are a subgroup of the Chromalveolates.
• Stramenopiles group contains Diatoms, Oomycetes and Brown algae.
• Brown algae - Haplodiplontic life cycle involves alternation of generations

  Sporophyte – multicellular and diploid.

  Gametophyte – multicellular and haploid.
• Diatoms

  Phylum Chrysophyta - Photosynthetic, unicellular organisms They have unique double shells made of silica and some move using raphes

  • Two long grooves lined with vibrating fibrils
• Oomycetes

  “Water molds” Either parasites or saprobes (decomposers)

  Were once considered fungi Motile zoospores with two unequal flagella • They Produced asexually. Undergo sexual reproduction Found in water. Cause of Irish potato famine.
• Rhizaria use pseudopods for locomotion. Three distinct monophyletic groups: Radiolaria, Foraminifera, and Cercozo
• Radiolarians - Glassy exoskeletons made of silica; Needlelike pseudopod
• Foraminifera - Heterotrophic marine protists

  Pore-studded shells called tests, through which thin podia emerge

  Use podia for swimming and feeding

  Complex life cycles with haploid and diploid generations

  Limestones are rich in forams (White Cliffs of Dove)
• Cercozoa - A morphologically diverse group of primarily soil protists Locomotion with flagella or pseudopods.

  Some have silicabased shells made of scales or plates.
• Archaeplastida - consists of Rhodophyta, Chlorophyta, Charophytes, and land plants. (photosynthetic organisms acquired their chloroplast through primary endosymbiosis)
• Rhodophyta - Red algae range from microscopic to very large

  Lack flagella and centrioles

  Have accessory photosynthetic pigments which are often red

  Have both haploid and diploid phas
• Green Algae Green algae consist of 2 lineages

  Chlorophyta. - Unusual diversity and lines of specialization. • Charophytes - Gave rise to the land plants
• Cell specialization in colonial chlorophytes Multicellularity arose many times in the eukaryotes

  ( Colonial chlorophytes are examples of cellular specializatiom)
• Charophytes have haplontic life cycles 2 candidate charophyte clades thought to be most closely related to land plants

  Both charophyte clades form green mats around the edges of freshwater ponds and marshes

  One species must have successfully inched its way onto land through adaptations to drying
• Amoebozoa Amoebas move by means of pseudopods

  • Pseudopods are flowing projections of cytoplasm.
  • -Extend and pull the amoeba forward. - Engulf food particles. •-An amoeba puts a pseudopod forward and then flows into it.
  • Microfilaments of actin and myosin are associated with these movements.
• Amoeba Most amoeba are free living • Found in the soil as well as freshwater. • Some are parasitic.
• Slime molds Important group for the study of cell differentiation because of their relatively simple developmental systems

  Individual organisms behave as separate amoebas

  Move through soil ingesting bacteria
• Opisthokants contain Fungi, Choanoflagellates and animals.
• Choanoflagellates -

  Unicellular organisms. •

  • Fungi and animal common ancestor. • Most like the common ancestor of sponges. • Have a single emergent flagellum surrounded by a funnel-shaped, contractile collar; structure is exactly matched in sponges, which are animals.
• Appearance of eukaryotes in microfossils occurred about 1.5 BYA