Origin of Life on Earth

• The phylogenetic tree shows the evolutionary relationships between cells, starting from the ancestral prokaryotes.

Earth's Early Atmosphere

• The early atmosphere has lots of methane and increased CO2.
• There was little to no oxygen and higher temperatures.
• Volcanic eruptions released energy, and there was no UV protection due to the absence of ozone.
• These conditions favored spontaneous reactions.

Formation of Carbon Compounds

• Living organisms altered spontaneous conditions, leading to the formation of carbon compounds.
• Reactions occurred under ideal conditions of high temperature and pressure.
• Catalysts like metals facilitated the self-assembly of polymers and self-replicating molecules like RNA.
• Compartmentalization occurred through spontaneous membrane formation by phospholipids, creating partially permeable structures.

The First Genetic Material - RNA

• RNA can store genetic information, self-replicate, and function as an enzyme.
• RNA mutates at a higher rate compared to DNA.
• Mutations allows for rapid adaptation to new environments.

Evolution of LUCA (Last Universal Common Ancestor of Cells)

• LUCA utilized compounds like HCHO, HCN, cyanamide, glyceraldehyde, and PO43-.
• Minerals acted as catalysts in high-temperature hydrothermal vents.
• The RNA world involved ribozymes.
• DNA became more stable, and lipid bilayers spontaneously formed vesicles.

Bacteria and Archaea

• Bacteria and archaea have a single cellular compartment without membrane-bound organelles.
• Some bacteria have specializations, such as flagella.
• There is a huge variety of bacteria and archaea.
• Archaea can adapt to extreme environments and sources of energy, and reproduce quickly, although with errors.

Mitochondria - The Endosymbiotic Theory

• Mitochondria have a double membrane and their own DNA.
• Mitochondria established a symbiotic relationship between archaea and bacterium.
• Chlorophyll-based photosynthesis occurs in green sulfur bacteria and heliobacteria (Photosystem I) and purple and green filamentous bacteria (Photosystem II).
• Cyanobacteria also play this role.
• Both sides benefited from the relationship.
• Genes in mitochondrial genome are very similar to bacterial genome.

Protozoans

• Protozoans are single-celled eukaryotes that exhibit motility and predation.
• They are distinct from animals, plants (algae), or fungi.

Multicellularity and Cellular Specialization

• Multicellularity is associated with specialization.
• Examples include heart cells, blood cells, kidney cells, neurons, gut epithelial cells, and bone cells.

Ex ovo omnia

• Asexual reproduction occurs in organisms like hydra and yeast.
• Sexual reproduction is different than parthenogenesis (eggs develop without fertilization), where offspring only contain maternal genetic information.
• Embryogenesis requires tight control of cell division, morphogenesis, and differentiation.

Origins of Multicellularity

• Volvox is a colonial green alga that demonstrates origins of multicellularity.
• Volvox carteri has two cell types, somatic cells (differentiated, mortal) and germ cells (gonidia, reproductive, immortal).

Origins of Social Behaviour

• Dictyostelium discoideum, or 'slime mold', is a social amoeba.

Display Characteristics of Multicellular Organisms

• It is easier to damage more complex organisms.
• Pathogens are disease causing microorganisms or infectious agents.
• Examples of pathogens include bacteria, viruses, fungi and protozoans

Bacterial Pathogens

• Robert Koch (1884) determined cholera is caused by a rod-shaped bacterium (Vibrio cholerae).
• Alexander Fleming (1928) discovered penicillin, which won a Nobel Prize for Medicine in 1945.
• Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to antibiotics.
• Cyanobacteria produce toxins, which have caused elephant deaths in rare cases.
• Archaea are not known to cause diseases because they live in extreme environments.

Viruses

• Outside of a host cell, a virus exists as a virion.
• A virion has DNA or RNA + protein coat/capsid + sometimes lipid envelope.
• Retroviruses can make DNA from RNA using reverse transcriptase, but lentiviruses have been linked to mutagenic integration events.
• Viruses can enter dormancy such as herpes virus/varicella-zoster virus.
• Viruses are typically very small (only visible in EM).

Other Pathogens

• Fungi and protozoans are also pathogens.
• Fungi include Candida albicans (yeast), Cryptococcus gattii (yeast), coccidioidomycosis (‘Valley fever'), athlete's foot'.
• Protozoans include malaria (Plasmodium falciparum and Plasmodium vivax), toxoplasmosis (Toxoplasma gondii; undercooked meat), giardiasis (Giardia species; 'beaver fever'), cryptosporidiosis (Cryptosporidium; diarrheal illness causing diarrhea).