Theme: Unity and Diversity - Level of Organization: Cells

Subtopics

• A2.1.1 - Conditions on early Earth and the pre-biotic formation of carbon compounds.

• A2.1.4 - Evidence for the origin of carbon compounds.

• A2.1.5 - Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers.

• A2.1.6 - RNA as a presumed first genetic material (HL – Higher Level).

• A2.1.7 - Evidence for a last universal common ancestor.

• A2.1.8 - Approaches used to estimate dates of the first living cells and the last universal common ancestor.

• A2.1.9 - Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents (HL).

Early Earth Conditions and Pre-biotic Formation of Carbon Compounds

• A2.1.1 - Conditions on early Earth and the pre-biotic formation of carbon compounds:

  • Early Earth had a reducing atmosphere (little to no free oxygen), volcanic activity, and intense UV radiation.

  • Key compounds like water, methane, ammonia, and hydrogen sulfide were present.

  • Energy sources included lightning, volcanic activity, and UV radiation, facilitating chemical reactions.

• A2.1.4 - Evidence for the origin of carbon compounds:

  • Miller-Urey experiment: Demonstrated that amino acids could be formed from inorganic precursors under early Earth conditions.

  • Analysis of meteorites: Carbonaceous chondrites contain amino acids, lipids, sugars, and nitrogenous bases.

  • Deep-sea hydrothermal vents: Provided environments rich in chemical energy and minerals for the synthesis of organic compounds.

• A2.1.5 - Spontaneous formation of vesicles by coalescence of fatty acids into spherical bilayers:

  • Fatty acids can spontaneously form vesicles in water, creating enclosed structures similar to cell membranes.

  • These vesicles can encapsulate other molecules, providing a mechanism for concentrating and protecting early biochemical reactions.

• A2.1.6 - RNA as a presumed first genetic material (HL – Higher Level):

  • RNA has simpler structure than DNA and can act as both a carrier of genetic information and a catalyst (ribozymes).

  • RNA world hypothesis: Suggests that RNA was the primary form of genetic material before DNA evolved.

Last Universal Common Ancestor (LUCA)

• A2.1.7 - Evidence for a last universal common ancestor:

  • Universal genetic code: All known life forms use the same set of genetic codons, suggesting a common origin.

  • Conservation of core metabolic pathways: Key biochemical pathways, such as glycolysis and ATP synthesis, are conserved across diverse organisms.

  • Ribosomal RNA (rRNA): Highly conserved sequences in rRNA genes are used to infer phylogenetic relationships and identify LUCA.

• A2.1.8 - Approaches used to estimate dates of the first living cells and the last universal common ancestor:

  • Molecular clocks: Using mutation rates in conserved genes to estimate the time of divergence between species.

  • Geological evidence: Analyzing ancient rocks and fossils to determine the age of the earliest life forms.

• A2.1.9 - Evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents (HL):

  • Hydrothermal vents provide a stable and energy-rich environment for early life.

  • Chemosynthesis: LUCA likely used chemosynthesis to derive energy from chemical compounds, such as hydrogen sulfide, available at hydrothermal vents.

  • Phylogenetic analysis: Indicates that the earliest branches of the tree of life are microorganisms that thrive in high-temperature environments, similar to those found near hydrothermal vents.