Lecture Notes for Honors 301T: Chapter 3

Also see helpful links related to Zimmer's Chapter 5 here (We read only the chapters 3 and 4 in the first two weeks.)

Eukaryote Novelties

Genetic material is inside nucleus
   nuclear DNA probably from archaean
   debated whether origin of nucleus was part of original cell or endosymbiotic

Cell wall flexible
   depends on eukaryotic cytoskeleton system
   flexibility depends on steroids in membrane
   permitted phagocytosis
   permitted endosymbiosis
   plants are secondarily rigid

   multiple origins of replication
   allowed larger genome size
   chromosomes not attached to cell wall
   chromosomes linear, not circular
   chromosome replication supported by spindle fibers

Sexual reproduction
   involves shuffling of the DNA in daughter cells (offspring)
   depends on reduction division (meiosis)
   might be a way to get rid of harmful mutations
   one cost is loss of parent's genetic contribution
   another cost is built-in break up of any combination of "good genes"

   Endosymbiotic in origin
   mitochondria have their own genome (mtDNA)
   mtDNA is most similar to DNA of purple nonsulfur bacteria
   oxidizing metabolism is also similar
   Probably absent in first eukaryotes
   Eukaryotes that lack mitochondria tend to be basal in rRNA phylogenies (e.g., Giardia)
   Recent conflicting evidence suggests that they once might have had mitochondria
    (they still make mtDNA proteins)
   Too early to resolve this paradox

   Endosymbiotic in origin
   plastids have their own genome (e.g., cpDNA in chloroplasts)
   this genome is most similar to cyanobacteria
   photosynthetic metabolism is also similar
   plastids have been acquired multiple times in eukaryotes
   recent evidence demonstrates that plastid-containing eukaryotes were often the symbionts
     in other eukaryotes, not cyanobacteria (secondary endosymbiosis)
   Euglena has a typical green chloroplast but it is relatively unrelated to green algae, suggesting
     it is a good example of acquiring plastids by secondary endosymbiosis
   a paper published in May, 2000 presents evidence that only one primary endosymbiosis
     event occurred (from cyanobacteria) (Nature 405: 32-33, and related article on p. 69)
     leading to three distinct groups of plastids (green chloroplasts, red algae, and "glaucophytes"
     including Cyanophora), however this paper has little to do with other sorts of eukaryotic plastids,
     for example, those found in kelp, diatoms, and dinoflagellates.

Review Questions for Honors 301T: Chapter 3

1. What are the most apparent differences between microbes ("prokaryotes") and eukaryotic organisms?

2. What is the evidence supporting the endosymbiotic theory of mitochondrial and plastid origins?

3. What are the most likely ancestors of mitochondria and plastids and why?

4. Why are the earliest eukaryotic fossils a paradox in terms of what their age would imply?

5. What is the relationship between mutations and natural selection?

6. What are some possible advantages and disadvantages of sexual reproduction?

7. What is the Linnean system of classification?

8. What is cladistics?

9. How do conventional and cladistic classifications differ with respect to how "reptiles" and "birds" are classified?

[Go to Previous: Review Questions for HOL Chapter 2]

[Go to Next: Review Questions for HOL Chapter 4]

[Go to History of Life listing for Chapter 3]

[Return to Honors 301T Home Page]