Topic 10 - Eukaryotes PDF

Topic 10 Eukaryotes Learning Outcomes • • • • • • • • • Compare prokaryotes and eukaryotes based on cellular characteristics Associate cellular structures of eukaryotes with their functions Justify why the evolution of multicellularity and sexual reproduction were key innovations Explain the bene...

Topic 10 Eukaryotes Learning Outcomes • • • • • • • • • Compare prokaryotes and eukaryotes based on cellular characteristics Associate cellular structures of eukaryotes with their functions Justify why the evolution of multicellularity and sexual reproduction were key innovations Explain the benefits of both sexual reproduction and asexual reproduction Place on a life cycle the ploidy level (n or 2n), mitosis, spores, meiosis, gametes, fertilization, zygote Differentiate between the three types of life cycles Name examples of protists Explain the heterozygote advantage against malaria for individuals that have sickle cell anemia Draw mutualistic beneficial relationships between a fungus and a plant, or between a fungus and an algae 2 https://www.wooclap.com/BIO1130 3 Topic 10 Eukaryotes 10.1 – Characteristics of eukaryotes Eukaryotes Eu- (true in Greek) and karyon- (nucleus in Greek). The group of eukaryotes is considered a monophyletic group à it contains the common ancestor and all of the descendants tes o y ar Euk Sea water Grypania spiralis (photosynthetic algae) Sediment 5 Eukaryotes Eu- (true in Greek) and karyon- (nucleus in Greek). The group of eukaryotes is considered a monophyletic group à it contains the common ancestor and all of the descendants First eukaryotic cells ~1,800My from endosymbiosis 6 Eukaryotes • 10-100µm in size typically • Plasma membrane which constitutes a selective barrier with the environment. • Cytoplasm: total content of the cell bounded by the plasma membrane (and excluding the nucleus): - Cytosol (internal fluid containing organic molecules, proteins, metabolic waste, etc.) - Organelles (membrane-enclosed structures with specialized functions) - Inclusions (particles of insoluble substances) ll l ce a im An • Nucleus: contains the genetic material in the form of chromosomes, made of chromatin (DNA + proteins) 7 Eukaryotes • Endoplasmic Reticulum (ER): membranous network, continuous with the outer nuclear membrane. à Rough ER (ribosome-studded): synthesis of proteins à Smooth ER: (ribosome-free): synthesis of lipids, carbohydrate metabolism, steroids, detoxification, calcium storage. • Golgi apparatus: protein and phospholipid modifications/trafficking ll l ce a im An • Mitochondrion: double membrane-bound organelle performing cellular respiration. Uses oxygen to break down organic molecules and synthesize ATP. Possess its own DNA (endosymbiosis). • Cytoskeleton: network of microtubules, microfilaments, and intermediate filaments (mechanical, structural, transport, motility and signalling functions). 8 Eukaryotes • Peroxisome: oxidative organelle containing enzymes transferring hydrogen atoms from various substrates to oxygen (O2), producing and then degrading hydrogen peroxide (H2O2) which is toxic for the cell. • Lysosome: digestive organelle (hydrolysis of macromolecules) ll l ce a im An 9 Eukaryotes • Peroxisome: oxidative organelle containing enzymes transferring hydrogen atoms from various substrates to oxygen (O2), producing and then degrading hydrogen peroxide (H2O2) which is toxic for the cell. • Lysosome: digestive organelle (hydrolysis of macromolecules) • Flagellum: long cellular appendage specialized for locomotion. Projects from the cytoskeleton and covered by the plasma membrane. Prokaryotic flagella have a very different structure! ll l ce a im An 10 Photosynthetic Eukaryotes Photosynthetic eukaryotes have both mitochondria and plastids (origin: endosymbiosis) • Plastids: family of closely related organelles: - Chloroplasts (photosynthesis) - Chromoplasts (fruit and flower pigmentation) - Amyloplasts (storage of starch = amylose) ell c t n Pla • Chloroplasts: organelle that absorbs sunlight and uses it for the synthesis of organic compounds from carbon dioxide (CO2) and water (H2O). Possess its own DNA. 11 Great variety among eukaryotes Many eukaryotes show structural variation and also the presence or absence of organelles! • Animal cells lack cell walls and lack chloroplasts. • Plant cells have a central vacuole, a cell wall (cellulose), plastids, often lack flagella • Fungi cells lack flagella, have a cell wall (chitin) and have less compartmentation between cells à passage of cytoplasm, organelles, nuclei… (syncytium: multinucleate cell deriving from cell fusion) Some eukaryotes show pseudopodia à cellular extension used in moving and feeding 12 Topic 10 Eukaryotes 10.2 – Sexual reproduction, life cycles and multicellularity Protists 14 Protists Paraphyletic group: includes the ancestor and some of its descendants. à not a taxon). Many branches are still phylogenetically unresolved and the classification still changes. 15 Protists Protists: Any eukaryote that is not a plant, animal, or fungus. Most of the eukaryotic lineages are protists! Most are unicellular but some are colonial or even multicellular. Large diversity in nutrition: • Photoautotrophs • Heterotrophs • Mixotrophs (combine photo- and heterotrophy). Large diversity in reproduction… • Asexual (division of the organism in two identical offspring) • Sexual (fusion of gametes) …and life cycles: • Haplontic/diplontic/haplo-diplontic 16 Sexual reproduction • Diploid (2n) individuals of the same species can produce haploid (n) reproductive cells through meiosis • These haploid reproductive cells often differ in size (anisogamy) • The union of these haploid gametes (n) produce a diploid zygote (2n): fertilization 17 Sexual reproduction Disadvantages of reproducing sexually: • It takes time and energy to look for a sexual partner (time spent not feeding) • An individual “dilutes” its own genes every generation (only half of its genes are passed on). • Reproductive output is decreased by half for a given sex (one sex does not contribute, often the males). à two-fold cost of sex. Advantages of reproducing sexually: • New genetic combinations can be beneficial in changing environments. • Elimination of deleterious alleles from the population. à can speed adaptation 18 Sexual reproduction nd Best ha • Many genes together contribute to an individual’s fitness in a specific environment. à The combinations between all the different alleles are like “poker hands” • Winning hands have combinations of cards that work well together à Winning hands have “survived” previous rounds (of selection) • Sexual reproduction breaks apart favorable gene combinations built by past selection à Shuffling your cards can produce new combinations that may or may not work well … if the rules change frequently, winners might be better off shuffling their cards!! … if the environment changes over time, genetic associations built up by past selection can become detrimental Consequence: sexual reproduction can…. …speed up adaptation in a changing environment …eliminate deleterious alleles (“bad poker hands”) and Worst h 19 Life Cycles Life cycle: generation-to-generation sequence of stages in the reproductive history of an organism. • 2 phases: haploid (n) and diploid (2n) 3 types of cycles: Diplontic life cycle: à multicellular diploid Haplodiplontic life cycle: à multicellular diploid à multicellular haploid Haplontic life cycle: à unicellular diploid 20 Diplontic Haplo-diplontic Haplontic 21 Unicellular Multicellular Multicellular eukaryotes appeared 25 times independently! First direct evidence: 1,200My • Increase in the surface area for diffusion • Longer lifespan • Specialization of cells into cell types, tissues and organs • Protection, feeding, locomotion, reproduction Ex: spherical colonies up to 50,000 cells: • Many flagellates somatic (outer layer) • Few germ cells (gonidia, inner layer) Grosberg et al 2007 Volvox sp. (green algae) 22 Topic 10 Eukaryotes 10.3 – A few examples 24 Protists Trichomonas vaginalis infects reproductive/urinary tracts. Diatoms: unicellular algae with hard walls made of silica (SiO2) Volvox sp. Paramecium caudatum (predators) Foraminifera (biomarkers of sedimentary rocks) 25 Protists Ex: Plasmodium, parasite transmitted by mosquitos that causes malaria (200M infected and 600,000 death/year). à Haplontic life cycle Anopheles gambiae Inside mosquito Sporozoites (n) MEIOSIS Oocyst MEIOSIS FERTILIZATION Life cycle of Plasmodium falciparum 26 Protists β-globin Malaria relative survival In regions where malaria is endemic, individuals with sickle cells anemia (mutation in the β-globin, “S” allele) have a survival advantage against malaria fatality over people with normal hemoglobin, “A” alleles. Genotype Red blood cells from AS individual Sickle cells anemia inhibits the parasite infection of the host. à Infected cells of S-carrier are destroyed before the parasite can reproduce and infect other cells à Heterozygote advantage and higher frequency of the “S” allele in those regions 27 Protists Dinoflagellates: possess two flagella Can bloom (explosive population growth): “Red tide” à coastal upwelling of nutrients (Nitrates, phosphates), à changes in temperatures, water pollutions, etc. Lingulodinium polyedra Bioluminescence: production and emission of light. Mechanical stress (predator avoidance) à converts chemical energy into light inside a (scintillon) 28 Myxomycetes (slime molds) E.g., Blob • • • • • • • • Unicellular Can be cut in many pieces Almost immortal Can move Synthesizes pigments Produces spores Can learn 720 sexes Physarum polycephalum 29 Fungi • Reproduce sexually and/or asexually. • Heterotrophs and decomposers. Saccharomyces cerevisiae Normal bacteria colony Growth inhibition zone Penicillium colony (fungus) Penicillium inhibiting bacterial growth (Fleming 1929) 30 Lichen (a symbiotic association, not an organism) Lichen = symbiosis between a green algae and a fungus) 31 Choanoflagellates Choanoflagellate Single posterior flagellum (propulsion) and chitin in their cell walls (as in exoskeleton, skin, of many animals). 32