Cells in their environment (lecture 2)

• LUCA (the last universal common ancestor of cells)


  Evolved from HCHO, HCN, cyanamide, glyceraldehyde, PO4^3- etc. Minerals as catalysts, high temperatures in hydrothermal vents. RNA world, ribozymes. DNA more stable. Lipid bilayers spontaneously form vesicles.
• Bacteria and archaea


  • One cellular compartment, no organelles
  • Specializations: e.g. flagella
  • Huge variety (approx. 1 mio species known)
  • Adapt to extreme environments (halophiles, thermophiles, acidophiles etc.) and sources of energy (hydrogen, methane, sulfate etc.)
  • Reproduction: error-prone, but fast
  • Our microbiome: 40,000 species, 30-50 trillion bacterial cells
• Endosymbiotic theory


  • Mitochondria: symbiotic relationship between archaea and bacterium
  • Chlorophyll-based photosynthesis: Photosystem I in green sulfur bacteria and heliobacteria, Photosystem II in purple and green filamentous bacteria, Cyanobacteria
• Protozoans


  • Single-celled eukaryotes
  • Motility, predation
  • Not animals, plants (algae) or fungi
• Ex ovo omnia


  Lat. 'Everything from the egg'. Sexual reproduction versus parthenogenesis. Embryogenesis requires tight control of cell division, morphogenesis and differentiation.
• Volvox (Volvox carteri)


  • Colonial green alga
  • Two cell types: somatic cells (differentiated, mortal) and germ cells (gonidia, reproductive, immortal)
• Dictyostelium discoideum


  • Motility and chemotaxis
  • Cell adhesion
  • Phagocytosis, micropinocytosis, autophagy
  • Pattern formation
  • Cell death
• Bacterial pathogens


  • Robert Koch (1884): cholera is caused by a rod-shaped bacterium (Vibrio cholerae)
  • Paul Ehrlich (1910): Salvarsan
  • Alexander Fleming (1928): penicillin – Nobel Prize for Medicine 1945
  • Multi-resistant Staphylococcus aureus (MRSA)
  • Cyanobacteria: produce toxins
• Archaea


  Not known to cause diseases
• Viruses


  • Outside of host cell: virion (DNA or RNA + protein coat/capsid + sometimes lipid envelope)
  • Retroviruses, lentiviruses (e.g. HIV) – integration events can be mutagenic
  • Dormancy (e.g. herpes virus, varicella-zoster virus)
  • Origins: 'virus first' versus 'cellular origin' hypotheses
  • Usually very small (only visible in EM)
  • 2013 Science: pandoravirus (2,500 genes)
• Other pathogens


  • Fungi: Candida albicans, Cryptococcus gattii, coccidioidomycosis ('Valley fever'), athlete's foot. Approx. 1 mio deaths per year globally.
  • Protists: malaria, toxoplasmosis, giardiasis ('beaver fever'), cryptosporidiosis
• The content of the recommended book (Pollard, Earnshaw, Lippincott-Schwartz, Johnson, Pollard (2017) Cell Biology. 3rd ed. Elsevier, PA) is broader than the learning outcomes of this module. Thus, do not panic - we do not expect you to study this book from the first to the last page. You should rather use it to supplement your learning and as a resource if you have a question or if you find a particular topic interesting and would like to learn a little bit more about it.