By: Alexandra, Isabel and Katharina

1. Prokaryotes VS. Eukaryotes By: Alexandra, Isabel and Katharina

2. What are they? • Prokaryotes: • small, simple cells that do not have a membrane-bound nucleus • Eukaryotes: • complex cells that have a membrane-bound nucleus and are larger than prokaryotes

3. How are they different?

4. More Differences

5. What do they contain?

6. Evolution • Eukaryotes evolved from Prokaryotes • 5 BILLION YEARS – the only organisms on Earth were prokaryotes • 2 BILLION YEARS AGO – Eukaryotes evolved from Prokaryotes, allowing for greater diversity • KEY QUESTION: How did eukaryotic organisms form from prokaryotes?

7. Endosymbiosis What it is: Endosymbiosis: • Widely accepted theory (not proven) stating that eukaryotes evolved from symbiotic relationships between prokaryotes • Endosymbiosis occurs when a prokaryotic cell consumes a different prokaryotic cell, the latter of which remains inside the former as an internal structure

8. Endosymbiosis Cont. • Endosymbiont: cell that is consumed in endosymbiosis • Host cell: Cell that consumes endosymbiont in endosymbiosis • This is called primary endosymbiosis • Secondary endosymbiosis: eukaryote is the host cell and prokaryote is the endosymbiont (same process as primary endosymbiosis) • e.g. much of algal evolution occurred due to secondary endosymbiosis

9. Proof for Endosymbiosis • Chloroplasts and Mitochondria • According to theory, chloroplasts and mitochondria were originally free-living prokaryotes • They were then engulfed by larger prokaryotic cells • They became internal structures of that host cell, continuing to function in the same way they did previously

10. Why were they endosymbionts? • Membranes are similar to those of prokaryotes • Ribosomes of organelles are more similar to those found in prokaryotes than eukaryotes • The organelles reproduce by binary fission • They each contain only one chromosome which contains genetic material resembling that of a prokaryote • Genetic composition of chloroplasts is similar to that of modern-day cyanobacteria

11. Evolution: Unicellular VS Multicellular • Endosymbiosis does NOT account for multicellularity, just greater diversity of unicellular organisms • 1.2 to 1.5 BILLION YEARS AGO – multicellular organisms came into existence • How multicellular organisms evolved from unicellular organisms: • The transition from unicellularity to multicellularity was driven by various selective pressures (e.g. cell-to-cell communication is a selective advantage) • Prokaryotes often congregate together in chains

12. Evolution: Unicellular VS Multicellular • Prokaryotic aggregations often: • Lack specialization • All carry out the same function • Harbour the same genetic material Cell aggregations • The aggregations are considered to be made up of individuals, not one individual • It has been hypothesized that multicellular organisms were formed from collections of dividing cells • These cells were specialized according to the genes within the cells, which coded for specialization

13. Evolution: Unicellular VS Multicellular • After thousands of years of evolution… • Different groups of cells could carry out different functions within multicellular organisms • KEEP IN MIND: multicellularity did not evolve only once; scientists have discovered at least 25 independent evolutionary lineages, branching off from each of the three domains

14. Reproductive Lifecycles • Eukaryotes • Complex cells; sexual and asexual reproduction • Through mitosis and meiosis • Three types of sexual life cycles: • Gametic • Zygotic • Sporic • Prokaryotes • Simple cells; asexual reproduction is common • Binary Fission (when conditions are favorable)

15. Sexual Life Cycles in Eukaryotes: Gametic • Gametic Meiosis • Gametes are produced through meiosis • Syngamy occurs (fusion of gametes in zygote) • Zygote undergoes mitosis to produce a multicellular organism • Gametes produced through meiosis, cycle continues • Common in animals and some protists

16. Sexual Life Cycles in Eukaryotes: Zygotic • Zygotic Meiosis (e.g. fungi) • Simplest sexual life-cycle • After fertilization, the zygote produces haploid cells (i.e. gametes) through meiosis • Mitosis occurs in the haploid cells for growth in the organism or to increase in number • Common within fungi and some protists

17. Sexual Life Cycles in Eukaryotes: Sporic • Sporic Meiosis (e.g. algae and plants) • Also referred as the alternation of generations • Simply stated: one generation reproduces sexually and the next asexually and so on, i.e. alternation • Results in the production of spores • Spore – reproductive cell that is able to produce multicellular organisms asexually (through mitosis)

18. Sporic Meiosis Cont. • Steps: • Zygote replicates through mitosis, forms the sporophyte (multi-cellular) • Sporophyte produces spores* (haploid cells) through meiosis • Spores grow asexually into multicellular organisms known as gametophytes • Gametophytes produce gametes • Gametes* fuse and form a zygote; cycle continues *(Spore – reproductive cell that reproduces asexually and thus without fusion (syngamy); Gamete – reproductive cell that reproduces sexually and thus through syngamy) http://www.hartnell.edu/tutorials/biology/lifecycles.html

19. Prokaryotic Reproduction • Asexual reproduction is common • Binary fission (division in half) • Occurs in most bacteria 1. Parent cell elongates and the single DNA molecule replicates 2. DNA divides 3. Key protein FtsZ assembles in the center of the cell (so that the cytoplasm can divide without damaging the DNA) 4. Cell wall and cytoplasm divide 5. New cell wall forms between divided DNA 6. Cytokinesis occurs https://www.youtube.com/ watch?v=5Xi2Nc1UicQ

20. Cell Reproduction: A Comparison

21. Questions • Which is not a real difference between prokaryotic and eukaryotic cells? • Prokaryotes don’t have a membrane-bound nucleus and eukaryotes do • Eukaryotic cells divide through mitosis or meiosis whereas prokaryotes don’t • Prokaryotes are multicellular, eukaryotes are unicellular • Prokaryotes are anaerobic, eukaryotes are aerobic • 2. Which of these organelles are proof of the endosymbiotic theory? • Nuclei and ribosomes • Mitochondria and vacuoles • Chloroplasts and mitochondria • Ribosomes and vacuoles

22. Questions Cont. • 3. Which statement isn’t true about the evolution of multicellularity? • Endosymbiosis is responsible for multicellularity • Prokaryotes evolved from eukaryotes • Prokaryotic chains are regarded as individuals rather than a collection • Multicellularityevolved several different times throughout history • 4. Prokaryotes reproduce through… • Gameticmeiosis • Sporicmeiosis • Zygotic meiosis • Binary Fission 5. Briefly describe the differences between primary and secondary endosymbiosis.