2.1 origin

prebiotic atmosphere

free oxygen was nearly absent

gases such as methane CH4, carbon dioxide, CO2, ammonia NH3, water vapor H2O

these gases were released through volcanic activity and meteorite bombardment

ozone layer

no oxygen o2 = no ozone layer o3, meaning that earth was exposed to UV radiation, which provided energy for the formation of organic molecules

high co2 levels

because of high concentrations of co2, methane and ammonia, the environment was highly reactive

absence of oxygen

The absence of oxygen was essential because oxygen’s high reactivity would have destroyed the fragile organic molecules forming

formation of carbon compounds

- combination of these conditions enabled chemical processes that no longer occur today.

- Under these conditions, simple carbon-based molecules like aldehydes, carboxylic acids, and formaldehyde formed spontaneously.

-UV radiation provided the activation energy needed for chemical reactions that would not normally occur today.

what makes something alive

1. All living organisms share a set of functions that define life.

2. Cells are the smallest units capable of carrying out these functions independently.

functions of life

mr h gren - metabolism, reproduction, homeostasis, growth, response to stimuli, excretion, nutrition

self sustaining life

ability to perform and carry out all functions of life without the need for external agents

metabolic regulation within a cell

cells use energy ATP to maintain internal order. without energy they lose structure or die

why are organelles not alive

Organelles perform specialized tasks inside cells, but none can live independently, for example protein synthesis ar dar ka nors

spontaneous origin of cells required four key steps:

1. Catalysis: speeding up reactions. (they lower the activation energy needed for the reaction to occur)

2. Self-replication: passing on information.

3. Self-assembly: forming complex molecules.

4. Compartmentalization: creating membrane-bound environments.

prebiotic earth catalysts

metal ions, clays, mineral surfaces

catalysts in modern cells

enzymes for protein catalysts, ribozymes for rna catalysts

rna as the first self-replicating molecule

because it can

Store genetic information (like DNA).

Catalyse reactions (as ribozymes).

polymers

Once organic monomers (like amino acids, nucleotides, and fatty acids) formed, they needed to assemble into polymers.

Prebiotic conditions such as heat, mineral surfaces, drying cycles, and UV radiation could have driven this process.

Resulting polymers:

1. Proteins (from amino acids)

2. Nucleic acids (from nucleotides)

3. Polysaccharides and lipids (from simpler precursors)

eg amino acids form polypeptides

birth of protocells

for true cells to emerge, components of life had to be separated from external environment for protection

1. Lipids naturally self-organize into bilayers, forming vesicles (protocells).

2. Compartmentalization allowed:

   1. Concentration of reactants inside membranes.

   2. Protection from external fluctuations.

   3. A distinct internal environment for controlled chemistry.

miller urey experiment

1. Miller and Urey proposed that Earth’s early atmosphere was reducing, containing gases such as methane (CH₄), ammonia (NH₃), hydrogen (H₂), and water vapor (H₂O).

2. They reasoned that these gases could react to form organic compounds when energy was supplied

abiogenesis

The origin of life from non-living matter, such as simple organic compounds.

miller-urey experiment steps

1. The experiment used a closed system of two connected flasks to simulate early Earth conditions.

2. Steps:

   1. Evaporation: Water was boiled to create water vapor (simulating the ocean).

   2. Gas Mixture: The vapor mixed with methane, ammonia, and hydrogen (simulating the atmosphere).

   3. Energy Source: Electrical sparks represented lightning, providing energy for reactions.

   4. Condensation: A condenser cooled the vapor, recycling liquid water back into the flask.

how to remember miller urey

• The system continuously cycled water and gases, mimicking Earth’s natural evaporation–condensation–lightning cycle.

• This constant recycling allowed ongoing chemical reactions, gradually producing more complex organic molecules over time.

miller - urey results

1. After several days, the solution turned reddish-brown and chemical analysis revealed over 20 amino acids and other simple organic molecules.

2. This demonstrated that organic compounds could form spontaneously under simulated early Earth conditions.

limitation of miller urey

1. Questionable Atmosphere Composition:

   1. Later evidence suggests early Earth’s atmosphere was neutral or mildly oxidizing, dominated by CO₂ and N₂, not strongly reducing gases.

   2. Under such conditions, amino acid formation is far less efficient.

2. No Direct Evidence for Life:

   1. The experiment produced amino acids, but not nucleotides or self-replicating molecules.

   2. It demonstrated chemical possibility, not the full origin of life.

Early Membranes and the Origin of Life

for life to emerge, internal chemistry had to be separated from external environment, therefore membranes provided this separation by compartmentalization

amphiphatic

A molecule with both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions, such as a phospholipid.

Amphipathic Molecules and Bilayers

1. On prebiotic Earth, amphipathic molecules like fatty acids were likely present in the "soup" of organic compounds.

2. Fatty acids have:

   1. Hydrophilic head: Polar, attracted to water

   2. Hydrophobic tail: Non-polar, repelled by water

3. When placed in water, these molecules naturally arrange to minimize energy:

   1. Polar heads face the water

   2. Non-polar tails cluster together, away from water

4. This makes bilayer formation spontaneous and self-organizing.

vesicle formation

amphipathic molecules form vesicles, which enclosed surrounding molecules.

the hydrophobic core of the bilayer acts as a barrier, limiting the movement of polar molecules between inside and outside

how vesicles enabled lifes building blocks

concentration of molecules, catalysts that enhance reaction and energy storage via ion gradients, where differences in ion concentration across the membrane stored energy.

RNA World Hypothesis

The RNA World Hypothesis is a scientific theory that suggests that RNA served as both the genetic material (storing information) and a catalyst(facilitating chemical reactions) before the evolution of DNA and proteins.

Ribozyme

A ribozyme is an RNA molecule capable of catalyzing specific biochemical reactions, similar to how protein enzymes function.

catalytic activity in rna

1. RNA can fold into complex 3D structures, that help position substrates, lower activation energy and create catalytic centers

2. Ribozymes (catalytic RNAs) have been found to:

   1. Join nucleotides.

   2. Catalyze peptide bond formation in ribosomes.

RNA’s Versatility in Laboratory Conditions

1. RNA molecules can evolve in laboratory settings to perform new catalytic functions.

2. This adaptability supports RNA's potential for diverse roles in the prebiotic world.

transition from rna to dna and proteins

modern life relies on dna for information storage and proteins for catalysts.

dna is chemically more stable due to absence of a hydroxyl group -OH

proteins are more versatile and efficient catalysts

specialization of roles and division of labor

Additional Evidence For The RNA World Hypothesis

1. RNA viruses (e.g., influenza, coronaviruses) use RNA as genetic material, demonstrating RNA alone can carry heredity.

2. Ribosomes rely on RNA for catalysis, showing RNA still retains ancient catalytic roles.

3. Deoxyribose (DNA) is derived enzymatically from ribose (RNA), suggesting DNA evolved later.

4. Laboratory studies show ribose and RNA nucleotides can form abiotically.

luca

it is believed that it is a common ancestor because everyone has the same genetic code, where dna sequences ATCG are translated into amino acids by creating codons

life appearance

formed 4.5 bln years ago

used fossil, isotopic, molecular evidence to estimate when life began

formation of earth

1. Earth emerged from a cloud of gas and dust in the early solar system.

primordial soup

1. Early Earth’s conditions enabled the formation of simple organic molecules, which accumulated in oceans, lakes, and pools.

2. This chemical "soup" set the stage for the emergence of life’s building blocks.

oldest evidence of life

stromatolites - fossils, which are layered rock structures formed by cyanobacteria

1. Their layered pattern resembles modern cyanobacterial mats.

2. Carbon isotope ratios (¹³C/¹²C) in these rocks suggest biological carbon fixation

timeline

genomic and molecular clock evidence

1. Molecular clocks estimate divergence times by comparing genetic differences between species.

2. Since DNA and proteins mutate at steady rates, scientists can back-calculate when two lineages shared a common ancestor.

3. Recent analyses suggest that LUCA existed between 4.2 and 4.5 Gya, close to when Earth stabilized after its formation.

hydrothermal vents

1. Hydrothermal vents are extraordinary environments where superheated water interacts with cold seawater, precipitating minerals like iron sulfides and silicates.

1. Fossils found in these rocks provide critical clues about microbial life on early Earth.

conditions in hydrothermal vents match conditions needed for adaption to an environment rich in hydrogen has h2, co2, iron compounds, 60-90 temperatures

conserved gene

a gene sequence that has remained largely unchanged across species due to its essential role in survival

functions of genes that are present in life inherited from luca

1. Anaerobic metabolism (energy generation without oxygen).

2. Carbon fixation (converting CO₂ into organic molecules).

3. Nitrogen fixation (reducing nitrogen to ammonia for amino acid synthesis).

4. Maintenance of ion gradients and primitive energy systems.