Unicellular Eukaryotes - Protists (Euglena, Amoeba and Paramecium)
Outline: -Characteristics of eukaryotes -Protists -Fungi -Plants -Animals.
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Transcript of Outline: -Characteristics of eukaryotes -Protists -Fungi -Plants -Animals.
Evolution of the nuclear envelope
Fig 20_1
-The nuclear envelope may have evolved gradually from the cell membrane
-As cells got bigger folded cell membranes allowed better access to external environment
-Eukaryote DNA is more similar in structure to archea than bacteria (introns)
Endosymbiotic theory: Mitochondria and Chloroplasts are derived from once free-living bacteria
Fig 20_2
-Mitochondria were free living aerobic bacteria
-Chloroplasts were free living photosynthetic bacteria (cyanobacteria)
-Each became incorporated into a eukaryotic cell, formed a symbiotic relationship, can no longer live outside of cells
Evidence that mitochondria were once free living bacteria
-Mitochondria are similar in size to bacteria
-Have their own DNA, circular without introns
-Use ribosomes that are similar to bacterial ribosomes for translation of RNA to proteins
-Divide by simple fusion
-Have a double layered membrane
Evidence that chloroplasts were once free living bacteria
-Posses circular DNA
-Use prokaryotic machinery
-Photosynthesis occurs using the 3 systems found in prokaryotes
The protists are the most basal eukaryotes
-Every eukaryrote that is not a plant, animal, of fungus is a protist (negative definition)
-Phylogeny not well resolved
-Evolved mitochondria and chloroplasts
-Evolved sex
-Evolved multicellularity
Sex evolved in protists
What is sex?
- Fusion of haploid gametes to form a diploid individual. Sex combines genomes from 2 parents
What is the advantage of sex?
- Greatly increases genetic diversity of a population, which improves adaptive ability of a population. In asexual populations diversity can only arise by mutation
What selection pressures lead to the evolution of sex?
- Stress
Protists have independently evolved multicellularity several times
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Fig 20_8
Phylogeny of protists - 5 major groups are not shown because their phylogenetic position is uncertain
Ancestors of plants
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Pg 385
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Fig 20_16
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Fig 20_17
-Red algae live in deeper marine environments
-Green algae are direct ancestors of plants, most are marine, few exceptions
-Exhibit alternating life cycle
Ancestors of animals
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Pg 387
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-Choanoflagellates are the ancestors of animals
-Single celled heterotrophs
-Filter feed bacteria from water
-May be colonial, resemble sponges
-Genetically closest group to animals
http://www.youtube.com/watch?v=tpdIvlSochk
The road to multicellularity - cooperation in dictyostelium discoideum
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Fig 20_24
Multicellularity
What is the advantage of being multicellular?
-Cell sizes are limited by surface to volume dynamics and physical-structural issues
-Cells can specialize
What is multicellularity?
-Multiple cells that are permanently associated with integrated activities
Colonial organisms
-Permanently associated cells with no coordinated activities
Aggregates
-Single cells that group together