ORIGINS

Discusses potential pathways for the biochemical formation of early life (Origin of life is an essential aspect to understand the evolution of all living organisms.)

Life's fundamental processes revolve around information transfer and storage through molecular systems.
DNA: Information is stored in the DNA.
RNA: The information in DNA is transcribed into RNA. The information contained in RNA is then translated to guide the synthesis of proteins.

Modern Metabolism Example:
- Sugars + O₂ → ATP + H₂O + CO₂
- Mitochondria and chloroplasts play pivotal roles in respiration (catabolic process) and photosynthesis (anabolic process).

Represents the evolutionary relationships between different organisms. LUCA (Last Universal Common Ancestor) is a key point in this evolutionary tree giving rise to all life forms.

Photosynthesis and Aerobic Respiration: These processes led to the development of complex eukaryotic cells.
The importance of oxygen accumulation made aerobic respiration possible.

The fossil record gives insights into the evolution and existence of early organisms.

Proposes that life started with RNA molecules.
  - RNA serves dual purposes:
    - Storage of Information: Similar to DNA.
    - Catalytic Functions: Comparable to proteins.
RNA is a plausible candidate for the first life form due to its ability to self-replicate and catalyze reactions.

Definition: Ribozymes are RNA molecules that possess catalytic properties and can facilitate reactions, supporting the RNA world hypothesis.
Modern existence of ribozymes illustrates the historical importance of RNA in early life processes.

The transition from RNA to DNA was gradual:
- Initially involved the formation of small DNA segments or RNA-DNA hybrids. This could have involved mechanisms like “patches,” primers, and repair processes.
- Ultimately, DNA evolved to encapsulate the genome.
DNA-RNA hybrids are crucial components in the DNA replication process.

Described as the oldest organelle, providing insight into the structure of early life.
The chemistry within ribosomes is performed predominantly by RNA, with proteins providing stability and improving efficiency.
Models suggest an RNA-peptide co-evolution process.

These are nutrient-rich environments where life may have originated:
- Acidic ocean water mixed with alkaline vent water creates potential energy gradients essential for life.
Conditions in these vents are key for primitive metabolic processes, potentially leading to the formation of protocells surrounded by inorganic membranes.

Gradients created by H₂ flow generate the potential energy that powers biological reactions.
H+ concentration differs between ocean water and vent water, driving energy-releasing reactions that could support early life forms through ATP formation.

Represents a common ancestor of all current organisms, including Bacteria, Archaea, and Eukarya.
Shared cell features with modern life:
  - Lipid bilayer
  - DNA → RNA → Protein paradigm
  - Presence of ribosomes
  - Proteins being principal structural and catalytic units.

Metabolism was primarily anaerobic, relying on:
  - H₂ as a hydrogen and electron source for energy.
  - CO₂ as a carbon source for macromolecule synthesis.
  - N₂ as a nitrogen source for building blocks such as proteins, DNA, and RNA.

The evolution of photosynthesis significantly contributed to the accumulation of oxygen in Earth’s atmosphere.
Cyanobacteria emerged as the first organisms to conduct oxygenic photosynthesis, using solar energy to convert CO₂ into sugars.
- This led to environmental changes that initially posed challenges to anaerobic organisms.
The rise of atmospheric oxygen marked the start of a major extinction event but also paved the way for the evolution of aerobic organisms, including complex eukaryotes.

Mitochondria and Chloroplasts arose from ancient aerobic and photosynthetic bacteria through a process of endosymbiosis where these prokaryotes merged into primitive eukaryotic cells.
Horizontal gene transfer played a role as endosymbiosis deepened, with integration of genes into the nuclear genome.

Gene transfer from chloroplasts to the nuclear genome, allowing for the synthesis of proteins necessary for organelle function.

The first evidence of life is dated to approximately 3.9 billion years ago based on geological and radiocarbon dating of ancient rocks.
Stromatolites, formed by cyanobacteria, are one of the earliest fossils found, dating back to about 3.5 billion years ago.
Oxidized iron deposits found in strata ~2.5 billion years ago indicate increasing oxygen levels in the atmosphere due to oxygenic photosynthesis, supporting the gradual buildup of life-sustaining conditions in Earth's history.