When were the older fossilized eukaryotic cells found?
Around 1.8 bya.
- photosynthetic cyanobacteria triggering the Great Oxygenation Event between 2.7 and 2.3 bya.
How do Eukaryotic cells differ from prokaryotic cells?
- Eukaryotic cells have DNA organized in linear chromosomes within a membrane-bound nucleus.
- Contain membrane-bound organelles, such as mitochondria and chloroplasts
- Generally much larger than prokaryotic cells
- Eukaryotes have a cytoskeleton and cellular dynamics, that enable them to change shape, move, and facilitate substance transfer in and out of the cell
- Can reproduce sexually which promotes genetic diversity in populations.
What is meiosis? What is fertilization?
Involves chromosome recombination and independent assortment of alleles
- during fertilization, the random fusion of gametes creates diverse combinations of alleles.
- The alternation of meiosis and fertilization is shared by all sexually reproducing organisms.
What is endosymbiosis? What is an endosymbiont?
Endosymbiosis is a symbiosis between two species in which one organism lives inside another organism’s cells or tissues.
- An endosymbiont is any organism residing within the body or cells of the host organism, typically in a mutualistic relationship.
What is the endosymbiont theory?
A theory that proposes that mitochondria and plastids were once small prokaryotes residing within larger host cells.
- this theory is supported by physical, biochemical, and genetic similarities between chloroplasts and cyanobacteria, and between mitochondria and alpha-proteobacteria.
What is serial endosymbiosis hypothesis of the origin of eukaryotes (step 1)?
- Ancestral prokaryote cells gradually developed endomembrane through infoldings of the plasma membrane (slide 7 for diagram)
- This gave rise to structures such as the endoplasmic reticulum and nuclear envelope
What is serial endosymbiosis hypothesis of the origin of eukaryotes (step 2)?
- Ancestral prokaryote cells engaged in an endosymbiotic relationship with an aerobic heterotrophic prokaryote, likely alpha-proteobacterium (slide 8 for diagram)
- This alpha-proteobacterium initially engulfed as prey or a parasite, evolved into a mutualistic endosymbiont
- This gave the host cell the ability to generate energy using oxygen and organic matter.
- This development marked the emergence of the ancestral heterotrophic eukaryote, a common ancestor for animals, fungi, and various protists
What is serial endosymbiosis hypothesis of the origin of eukaryotes (step 3)?
- A lineage of ancestral heterotrophic eukaryotes acquired an additional endosymbiont, a photosynthetic prokaryote (autotroph), likely a cyanobacterium (slide 9 for diagram).
- Using light and CO2, this endosymbiont synthesized organic compounds and eventually transformed into the chloroplast.
What does serial endosymbiosis hypothesize? What is the difference between primary and secondary endosymbiosis?
Serial endosymbiosis hypothesizes that mitochondria evolved before plastids in a series of primary endosymbiotic events.
- In primary endosymbiosis, prokaryotic cells are engulfed as endosymbionts by either prokaryotic or eukaryotic cells
- In secondary endosymbiosis, eukaryotic cells themselves become endosymbionts, being taken up by other eukaryotic cells.
What is some of the evidence behind endosymbiotic theory?
- Mitochondria and plastids (chloroplasts) share structural similarities with bacteria, such a double membranes and their own circular DNA.
- Phylogenetic analyses of mitochondrial and plastid genomes are most similar to the genomes of alpha-proteobacteria and cyanobacteria
- Mitochondria and plastids replicate independently within the eukaryotic cell by binary fission
- Mitochondria and plastids have their own machinery for protein synthesis which resembles that of bacteria
What are the evolutionary advantages to multicellularity?
- Cell specialization: a division of labor among cells with distinct functions
- Increased organismal size and complexity
- Extended life span
- Predation avoidance
What is the origin of multicellularity
Multicellularity evolved independently in various lineages leading to the development of algae, plants, fungi, and animals
- larger and more diverse multicellular eukaryotes are not prominent in the fossil record until around 600 mya.
What are the three domains that organisms are classified into?
Bacteria, Archaea, and Eukarya
Which domains are more closely related to each other? Has there been significant exchange observed between organisms from different domains?
- Eukaryotes and archaea are more closely related to each other than they are to bacteria.
- There has been significant genetic exchange between organisms from different domains.
- Horizontal gene transfer has contributed to genetic exchange between domains.
How has horizontal gene transfer contributed to evolution of prokaryotes and eukaryotes?
- Discrepancies in molecular phylogenies can be attributed to the occurrence of horizontal gene transfer
- HGT has played a crucial role in the evolution of prokaryotes and eukaryotes.
- some biologists argue that HGT was so common that the early history of life could be represented as a complex network of interconnected branches (suggesting a more intricate and tangled evolutionary pattern).
What is a protist?
An informal designation for a taxonomically diverse group of mostly unicellular eukaryotes
- not a monophyletic group! It specifically excludes plants, animals, and fungi.
- most eukaryotes are protists, and most protists are unicellular
- Many protists have evolved to exploit environments associated with animals and plants, and some cause human diseases.
What are some examples of protist diversity?
Protists exhibit more structural and functional diversity than any other group of eukaryotes.
- single-celled protists surpass multicellular eukaryotes in terms of complexity
- every biological function is carried out within each cell through various organelles.
- Protists can reproduce via asexual or sexual reproduction, like meiosis or fertilization.
- A large portion of protist diversity originated through endosymbiosis
What are mixotrophs?
Use a combination of photoautotrophic and chemoheterotrophic nutrition.
- photoautotrophs use photosynthesis while chemoheterotrophs absorb organic molecules or ingest larger food particles.
What is the evolution of photosynthetic protists?
The plastid-bearing lineage of protists originating from #1 endosymbiosis evolved into photosynthetic protists known as red an green algae
- photosynthetic protists also arose from secondary endosymbiosis (red and green algae being ingested by a heterotrophic eukaryote)
What is the four supergroups hypothesis?
Clades of protists being organized into the four super groups Excavata, SAR, Unresolved, Archaeplastida (kingdom plantae), and Unikonta.
