Protists

• Four Eukaryote Supergroups

  • Excavata
  • SAR
  • Archaeplastida
  • Unikonta
• All protists are eukaryotes
• Organelles in a eukaryotic cell

  • Cytoplasmic membrane
  • Cell wall
  • Nucleus
  • Endoplasmic Reticulum
  • Mitochondrion
  • Golgi apparatus
  • Ribosomes
  • Chloroplast
• Majority of protists are single-celled
• Some protists are photoautotrophic, termed 'Algae'
• Some protists are heterotrophic, termed 'Protozoa'
• Some protists are mixotrophic, performing both photoautotrophy and heterotrophy
• Differences between prokaryotic and eukaryotic cells

  • Cell size
  • Nucleus
  • Number of Chromosomes
  • Mitosis
  • Membranous organelles
  • Cell wall
  • Cytoplasmic ribosomes
  • Ribosomes in organelles
  • Cilia
  • Flagella
• PROTOZOA are single-celled animals
• Viewing protist cells is done through microscopy, known as a 'total cell count'
• Record holder: Largest amoeba is 10cm (deep sea)
• Similarities to bacteria include Cytoplasmic membrane, Cell wall, Nucleus, Endoplasmic Reticulum, Mitochondrion, Golgi apparatus
• Cell components

  • Plasma membrane (separates cytoplasm from the outside)
  • Cell wall (plants & fungi; gives structural strength)
  • Nucleus – membrane enclosed (contains DNA)
  • Endoplasmic Reticulum (ER; protein glycosylation, membrane factory, lipid synthesis)
  • Mitochondrion (respiration)
  • Golgi apparatus (modifies, stores, routes products of the ER)
  • Ribosomes (protein synthesis)
  • Chloroplast (plants & algae; photosynthesis)
  • Diagram of a eukaryotic cell (simplified!)
  • Cytoskeleton (e.g. tubulin, actin, throughout cytoplasm)
  • CYTOPLASM
• Differences between prokaryotic and eukaryotic cells

  • Cell size: mostly small <5 μm (Prokaryote), larger than 5 μm (Eukaryote)
  • Nucleus: no (Prokaryote), yes (Eukaryote)
  • No. of Chromosomes: commonly one (Prokaryote), more than one (Eukaryote)
  • Mitosis: no (Prokaryote), yes (Eukaryote)
  • Membranous organelles: no (Prokaryote), mitochondria, Golgi apparatus, chloroplasts, ER, etc. (Eukaryote)
  • Cell wall: thin and thick or absent (Prokaryote), usually peptidoglycan (Eukaryote)
  • Cytoplasmic ribosomes: 70S (Prokaryote), 80S (Eukaryote)
  • Ribosomes in organelles: none (Prokaryote), 70S (Eukaryote)
  • Cilia: no (Prokaryote), yes (Eukaryote)
  • Flagella: yes, helical arrangement (Prokaryote), yes, 9:2 fibril arrangement (Eukaryote)
• Both prokaryotic and eukaryotic cells carry out asexual reproduction
• Bacteria reproduce through binary fission, while protists reproduce through mitosis
• Doubling time: E. coli – 20 mins at 37°C, Protists – hours/days at 37°C
• Daughter cells: Bacteria are identical, Protists are genetically identical but may vary in other components
• Cells adjust to new environment, grow exponentially, have a constant doubling time, and maximal growth rate
• Cells can no longer reproduce but are still alive when there is no food left, leading to death or cyst formation
• Advantages of cysts include being highly resistant to heat, drying, radiation, having very low water content, surviving for years, good resistance to antibiotics/disinfectants, effective dispersal mechanism, and being transmitted via faeces
• Most bacteria possess a cell wall, while some protists have cell walls and some do not
• Cell wall presence in different protists

  • Cell wall always present in non-motile photosynthetic protists like Diatoms, Cell wall not present in motile photosynthetic protists, heterotrophic protists, mixotrophic protists
• Cell walls of cysts prevent osmosis, leading to more water and less water inside the cell
• In an isotonic environment, there is no osmosis, maintaining water balance
• Need to overcome osmosis
• Cytoplasm

  NO CELL WALL LEADS TO OSMOSIS
• Cytoplasm

  CELL WALL OF CYSTS – NO OSMOSIS
• Cytoplasm

  IF IN ISOTONIC ENVIRONMENT - NO OSMOSIS
• Temperature and protist growth


  Cut off
• Oxygen and protist growth

  (in the main) Oxygen high, low
• Oxygen requirements for different types of protists

  • Obligate aerobes
  • Obligate anaerobes
  • Facultative anaerobes
  • Microaerophilic
  • Aerotolerant anaerobes
• AEROBIC

  Mitochondria O2 CO2 RESPIRATION - production of adenosine triphosphate (ATP)
• ANAEROBIC


  Hydrogenosomes Pyruvate H2, Acetate, CO2
• Endosymbiont theory: Mitochondria and plastids originated from bacteria living as endosymbionts in cells
• Digestion in paramecium: acidic, Insoluble debris, Membrane recycling, Food vacuole (phagosome) dynamics in protists
• Organellar Mixotrophy: Eats algal cells, Does not digest plastids, Plastids fix CO2, Protist can live without the plastids
• Cellular Mixotrophy: Eats algal cells, No digestion of algae, Algae fix CO2, Protist can live without the algae
• Constitutive mixotrophs: Over time, Endosymbiotic algae become true organelles, Protist cannot live without them
• Mixotrophy: Organellar, Cellular, Constitutive