Eukarya: Origin & Diversification of Eukaryotes - PDF

Assignment: Reading 2 for next class (required) BIO 102 CHAPTER 26: THE ORIGIN AND DIVERSIFICATION OF EUKARYOTES Dr. Ivonne Bejarano Earth’s Clock Life Prokaryotes were the first forms of life on Earth (3.8 bya). * Life...

Assignment: Reading 2 for next class (required) BIO 102 CHAPTER 26: THE ORIGIN AND DIVERSIFICATION OF EUKARYOTES Dr. Ivonne Bejarano Earth’s Clock Life Prokaryotes were the first forms of life on Earth (3.8 bya). * Life consisted only of unicellular life for >2 billion years. * H. sapiens on Earth ~300,000 years Cyanobacteria evolved the ability to photosynthesize- O2. Eukaryotes appeared 2 billion years ago. * eukaryotic cells evolved from prokaryotic cells- Unicellular eukaryotes first. Then, multicellularity arose.... Eukaryotes evolution What do we know about the common ancestor of Eukaryotes? Was a prokaryote archaea. Acquired organelles: e.g. nucleus, mitochondria, chloroplasts. The evolution of the eukaryote cell happened in a number of steps: 1. The loss of the cell wall: To allow a flexible cell surface that could grow larger and increase in volume. But…. cell volume increases proportionally with metabolic activity! Membrane Infolding Nutrients/gas exchange is proportional to surface area. Increased cell size cause the ratio surface area/volume to decrease. This is problems… why? At some point, exchange is too slow to support metabolism. But surface was flexible… folded inward and increased the surface area for more rapid exchange. New enclosed environments formed and had unique chemical reactions: e.g. the nucleus and nuclear envelop.  Cell wall lost Compartmentalizat ion Nucleus Stronger cytoskeleton Internal membranes with ribosomes Lysosomes… What was next?! Eukaryotes evolution 3. The new flexible cell membrane allowed phagocytosis and endosymbiosis. * At this time cyanobacteria were already photosynthesizing (O2). Endosymbiotic theory (until min 4): https://www.youtube.com/watch?v=4LhBZ2H5SwM 1. A large archaea engulfed but did not digest a proteobacteria, which evolved into the mitochondria. * the bacteria detoxified oxygen (reduced it to water). In photosynthetic eukaryotes there were additional endosymbiotic events: 2. Primary endosymbiosis 3. Secondary endosymbiosis 4. Tertiary endosymbiosis Primary endosymbiosis Photosynthetic eukaryotes. Some early eukaryotes (with mitochondria) engulfed and retained a cyanobacteria, gaining the ability to photosynthesize. This gave rise to chloroplasts with 2 membranes (ancestral and host plasma membranes). It was a gram-negative cyanobacteria. Peptidoglycan was lost, but remnants are present in some groups. Chloroplasts in glaucophytes, green algae, red algae, and land plants are all similar, with 2 membranes. Secondary and tertiary endosymbiosis Additional endosymbiotic events gave rise to chloroplasts in other eukaryotes. For example: photosynthetic Euglenid. Early eukaryotes (with mitochondria) engulfed and retained a green algae, another early eukaryote that already had a 2-membrane chloroplast. * these chloroplasts have 3 membranes. Domain Eukarya Eukaryotes We are quite familiar with most multicellular eukaryotes: e.g. plants, animals, or fungi… but not with unicellular eukaryotes, and they are common For example, and numerous. what are these organisms? Eukaryotes that are neither plants, animals, or fungi are called PROTISTS. Most groups of eukaryotes are “Protists”!! What is a protist? Protist is a “garbage bin” classification- not scientific. Eukaryotes is a “monophyletic group”: It includes all and only the descendants of a common ancestor. Protist is a “paraphyletic group”: It does not include all and only the descendants of a common ancestor. Protists 1. Excavata: e.g. photosynthetic euglena Unicellular. With feeding grove on one side of the cell. 2. Chromalveolata: 2.1. Alveolates: unicellular, with sacs “alveoli” in the cell membrane.  Dinoflagellates unicellular, have two flagella. most are photosynthetic, so they’re important primary producers. important endosymbiotic organisms. can cause red tides. Coral polyps produce CO2 that the zooxanthellae use for photosynthesis. Polyps grow with the sugars, lipids and oxygen of photosynthesis.  Red tides Certain dinoflagellates produce neurotoxins, and a bloom of them produce large amounts of toxins that harm marine life, like fish, marine mammals and seabirds. Filter-feeding organisms (like mussels and oysters) may accumulate these toxins as well, and if are eaten by humans it can be fatal for them.  Ciliates Have cilia for precise locomotion and to transport food into their gullet. Have 2 types of nuclei: macronucleus- for the cell’s functions micronucleus- for genetic recombination Conjugation: ciliates exchange genetic information without reproducing. Provides new combinations of genes. Is common in response to an unfavorable environment.  Ciliate Conjugation Two ciliates get together and fuse in the oral region. Micronuclei divide, and cells exchange micronuclei. The macronuclei disintegrate, and 2 micronuclei fuse to form a new macronucleus. Apicomplexans: Parasites with apical complex (organelles in the tip of the cell, that helps them invade the host tissue). Have complex life cycles that require two different organisms. * for example: Plasmodium-malaria (human- mosquito) In the mosquito body: human blood with plasmodium sexual cells are transformed into infecting cells, which accumulate in their salivary glands. When the mosquito bites someone, infecting cells pass to the human blood. In the human body: Infecting cells enter liver cells, multiply, and mature to go back to bloodstream and invade red blood cells to form sexual cells. 2. Chromalveolata: 2.2. Stramenopiles: e.g. diatoms, brown algae. Unicellular and multicellular, with a “hairy” flagellum. Diatoms Form beautiful silica frustules; look like petri dishes. Unicellular photosynthetic: produce 1/5 oxygen on Earth, similar to all rainforests. Produce oil to store energy and to float in upper photic zone. When die, sink to ocean floor and …. Reading 2 Brown algae Not plants! The brown color is due to the presence of fucoxanthin, a pigment to capture light at deeper depths. Include the largest protists there are: the giant kelps (up to 60 m long). Resemble plants: - Attached to hard bottom by a holdfast. - Have blades (leave-like structures) with gas bladders (to remain upright in the water to get more light closer to the  3. Rhizaria: Forams: Tiny amoeba-like organisms with calcium carbonate or inorganic tests that form sediments and sedimentary rocks. Their shells accumulate in sediments on the ocean floor and form sedimentary bedrock. Geologists use foram fossils to understand the geological history of an area, and Earth's climatic past. https://www.amnh.org/shelf-life/microfossils (Min1 to 4. Amoebozoa Amoeba: Unicellular organisms that change their shape with pseudopods (temporary arm-like projections developed in the direction of movement). Some are pathogens. Closing Protists!! Most eukaryotes are “Protists” Now moving into Non-protist eukaryotes!! Next stop: Plants!!