Protists (Lec 4) PDF

Three domains Prokaryotes: Bacteria and Archaea Eukaryotes: Eukarya NB You do not need to learn this map! Four Eukaryote Supergroups Excavata SAR Archaeplastida Unikonta ‘Protists’ in yellow NB You do not need to learn this map! Campbell, Chapter 28 All protists are eukaryotes Majority = single...

Three domains Prokaryotes: Bacteria and Archaea Eukaryotes: Eukarya NB You do not need to learn this map! Four Eukaryote Supergroups Excavata SAR Archaeplastida Unikonta ‘Protists’ in yellow NB You do not need to learn this map! Campbell, Chapter 28 All protists are eukaryotes Majority = single-celled Nucleus – membrane enclosed (contains DNA) Endoplasmatic Reticulum (ER; protein glycosylation, membrane factory, lipid synthesis) Cytoskeleton (e.g. tubulin, actin, throughout cytoplasm) Cytoplasmic membrane (separates cytoplasm from the outside) Cell wall (plants & fungi; gives structural strength) Mitochondrion (respiration) Golgi apparatus (modifies, stores, routes products of the ER) Chloroplast (plants & algae; photosynthesis) Ribosomes (protein synthesis) Diagram of a eukaryotic cell (simplified!) Cytoskeleton for trafficking organelles Protists • Some are photoautotrophic – ‘Plastids’ (green, red or golden) – Green plastid = “Chloroplast” – Photosynthesis (Campbell, Chapter 11) – Termed ‘Algae’ (some have a cell wall) • Some are heterotrophic – Feed on bacteria, fungi and other protists – Termed ‘Protozoa’ (‘first animals’) (none have a cell wall) • Some are mixotrophic – do both (none have a cell wall) Differences between prokaryotic and eukaryotic cells Feature Prokaryote Eukaryote Cell size Nucleus? No. of Chromosomes Mitosis Membranous organelles? mostly small <5 μm no commonly one no no Cell wall thin and usually peptidoglycan 70S larger than 5 μm yes more than one yes mitochondria, Golgi apparatus, chloroplasts, ER, etc. thick or absent Cytoplasmic ribosomes Ribosomes in organelles Cilia? Flagella ? none no yes, helical arrangement 80S 70S yes yes, 9:2 fibril arrangement PROTOZOA 2-5 mm 0.005 mm (5 µm) Single-celled animals 5-200 µm in size Record holder: Largest amoeba is 10cm (deep sea) Viewing protist cells (same as bacteria) microscopy Known as a ‘total cell count’ Need to ‘fix’ motile cells beforehand Similarities to bacteria (with reference to Lectures 1-3) Similarities to Prokaryotes CYTOPLASM Nucleus – membrane enclosed (contains DNA) Endoplasmatic Reticulum (ER; protein glycosylation, membrane factory, lipid synthesis) Cytoskeleton (e.g. tubulin, actin, throughout cytoplasm) Cytoplasmic membrane (separates cytoplasm from the outside) Cell wall (plants & fungi; gives structural strength) Mitochondrion (respiration) Golgi apparatus (modifies, stores, routes products of the ER) Chloroplast (plants & algae; photosynthesis) Ribosomes (protein synthesis) Diagram of a eukaryotic cell (simplified!) Differences between prokaryotic and eukaryotic cells Feature Prokaryote Eukaryote Cell size Nucleus? No. of Chromosomes Mitosis Membranous organelles? mostly small <5 μm no commonly one no no Cell wall thin and usually peptidoglycan 70S larger than 5 μm yes more than one yes mitochondria, Golgi apparatus, chloroplasts, ER, etc. thick or absent Cytoplasmic ribosomes Ribosomes in organelles Cilia? Flagella ? none no yes, helical arrangement 80S 70S yes yes, 9:2 fibril arrangement Both carry out asexual reproduction but… • Bacteria = binary fission • Protists = mitosis – Campbell, Chapter 12 • Doubling time – E. coli – 20 mins at 37oC – Protists – hours/days at 37oC • Daughter cells – Bacteria – identical – Protists – genetically identical but may vary in other components Log (Number of cells) Same population growth curve as bacteria Time (hours) Time interval between inoculation and maximal division rate: Cells adjust to new environment Grow exponentially: • Constant doubling time • Growth rate is maximal Can no longer reproduce but are still alive (e.g., no food left) Death or cyst formation Advantages of cysts • Same as advantages as for bacterial endospores: – – – – – – Produced under unfavourable conditions Highly resistant to heat, drying & radiation Very low water content Can survive for 20 years in the environment Good resistance to antibiotics/disinfectants Effective dispersal mechanism • Can be transmitted to others via faeces Differences to bacteria Differences to Prokaryotes Nucleus – membrane enclosed (contains DNA) Endoplasmatic Reticulum (ER; protein glycosylation, membrane factory, lipid synthesis) Cytoskeleton (e.g. tubulin, actin, throughout cytoplasm) Cytoplasmic membrane (separates cytoplasm from the outside) Cell wall* (plants & fungi; gives structural strength) Mitochondrion (respiration) Golgi apparatus (modifies, stores, routes products of the ER) Chloroplast (plants & algae; photosynthesis) Ribosomes (protein synthesis) Diagram of a eukaryotic cell (simplified!) Cell walls • Most bacteria possess a cell wall. • Some protists have cell walls, some do not. • Cell wall always present in… – Non-motile photosynthetic protists • E.g. Diatoms (not included in lectures 4-6) – Different structure to bacteria (e.g. cellulose, silica) – Cysts!! • Cell wall not present in... – – – – Motile photosynthetic protists Heterotrophic protists Mixotrophic protists (included in lectures 4-6) …need to overcome osmosis NO CELL WALL LEADS TO OSMOSIS Cytoplasm More water Less Water H2O Water naturally moves into the cell due to a concentration gradient CELL WALL OF CYSTS – NO OSMOSIS Cytoplasm More water H2O Less Water IF IN ISOTONIC ENVIRONMENT - NO OSMOSIS Cytoplasm Same water H2O Same Water Isotonic: Internal and external water content is equal Marine protozoa, pathogens Temperature and protist growth Cut off Oxygen and protist growth (in the main) Oxygen high low Obligate aerobes Need O2 for growth Obligate anaerobes Cannot grow in presence of O2 Facultative anaerobes Can grow with and without O2 Aerotolerant anaerobes Do not need O2, but tolerate it Microaerophilic Need O2, but tolerate it only at low concentration RESPIRATION - production of adenosine triphosphate (ATP) Campbell, Chapter 10 AEROBIC O2 CO2 Mitochondria ANAEROBIC H2, Acetate, CO2 Pyruvate Hydrogenosomes BROCK page 626 and pdf on Moodle Endosymbiont theory • For mitochondria and plastids – Bacteria originally living as endosymbiont in cells – Dependency then became permanent • Alpha-proteobacterium became a mitochondrion – Hydrogenosome evolved from a mitochondrion • Cyanobacterium became a chloroplast • Evidence for it, – Size of organelle = size of bacterium – Phylogeny analysis relates their DNA to their bacterial origin – Have own circular DNA and replicate by binary fission • Unequal distribution in daughter cells – Contain same ribosomes as bacteria – They have a double membrane (engulfing mechanism) Food Digestion vacuolein (phagosome) dynamics in protists paramecium acidic Membrane recycling Insoluble debris Food Digestion vacuolein (phagosome) dynamics in protists paramecium acidic Membrane recycling Insoluble debris Selective digestion or no digestion – leads to Mixotrophy Organellar Mixotrophy (Selective digestion) • Eats algal cells • Does not digest plastids (“Kleptoplastids”) • Plastids fix CO2 • Plastids do not encode for polymerases • Die and need replenishing (so eats more) • Protist can live without the plastids SWAG Cellular Mixotrophy (No digestion) Happy hour • • • • • • Eats algal cells No digestion of algae Algae fix CO2 Algae divide in cell “Endosymbiosis” Protist can live without the algae Party over here Constitutive mixotrophs (algae evolve into organelles) • Over time… • …and through complicated genetic transfer events (!) • Endosymbiotic algae become true organelles • Protist cannot live without them • Only seen in flagellates Mixotrophy • Organellar – Ciliates and amoebae • Cellular – Ciliates and amoebae • Constitutive – Flagellates • High light: Photosynthesis > feeding • Low light: Feeding > photosynthesis MOVEMENT for searching and capturing prey/light FLAGELLATES Flagellum/flagella CILIATES Cilium/Cilia AMOEBAE Cytoplasmic streaming