Origin of Life on Earth

Conditions of Early Earth

• Early Earth had a reducing atmosphere, high temperatures, UV radiation, volcanic activity, and asteroid bombardment.

Miller-Urey Experiment

• The Miller-Urey experiment demonstrated that simple organic molecules could form from inorganic compounds under early Earth conditions.

Early Genetic Material and Catalysts

• RNA is hypothesized to have been the first genetic material and catalyst in early cells.

Vesicle Formation

• Vesicles form spontaneously by the coalescence of fatty acids into spherical bilayers.

LUCA

• LUCA is the Last Universal Common Ancestor of all life on Earth.
• LUCA was the most recent common ancestor of all current life forms, estimated to have lived about 3.8 billion years ago
• Other life forms existed before or alongside LUCA but were outcompeted or went extinct, leaving LUCA as the sole survivor whose descendants evolved into all modern life.
• Scientists believe other life forms existed before or alongside LUCA but were outcompeted or went extinct, leaving LUCA as the sole survivor whose descendants evolved into all modern life.
• The universal genetic code is shared by all living organisms
• Common biochemical features across all domains of life, such as similar metabolic pathways, ATP as an energy currency, and RNA/DNA for genetic information

Obligate Aerobes vs. Obligate Anaerobes

• Obligate aerobes require oxygen, while obligate anaerobes are inhibited or killed by oxygen.
• Obligate aerobes require oxygen for survival and can only live in oxic (oxygen-containing) environments, while obligate anaerobes are inhibited or killed by oxygen and can only live in anoxic (oxygen-free) environments.
• Facultative anaerobes can use oxygen when available but can also survive without it, allowing them to live in both oxic and anoxic environments

Prokaryotic Cell Structure

• A nucleus is NOT a typical structure found in prokaryotic cells; prokaryotes have a nucleoid region with naked DNA, not a membrane-bound nucleus.
• Cell wall provides structural support and prevents the cell from bursting due to osmotic pressure.
• Nucleoid is the region containing the circular DNA that controls cell activities and reproduction
• Ribosomes (70S) are responsible for protein synthesis

Methanogenic Archaea

• Methanogenic archaea are chemoautotrophs that produce methane through anaerobic respiration.
• Methanogenesis is a metabolic process performed by some archaea where they produce methane (CH4) by reducing carbon dioxide with hydrogen (CO2 + 4H2 → CH4 + 2H2O)
• Methane produced becomes a potent greenhouse gas contributing to global climate change and methanogenic archaea in ruminant animals (cattle, sheep) are responsible for about 16% of global methane emissions.
• Extremophile archaea can be found in various extreme environments including hot springs, salt lakes, and deep-sea vents.

Evidence for LUCA

• The universal genetic code found in all living organisms supports the existence of LUCA.

Abiogenesis Steps

• The correct sequence for the hypothesized steps of abiogenesis is: Formation of simple organic molecules → Polymerization → Self-replication → Packaging.

Facultative Anaerobes

• Facultative anaerobes can survive with or without oxygen

Significance of Archaea

• A distinct feature of archaea is their ability to perform methanogenesis, producing methane, which makes them important in the global carbon cycle. Archaeal extremophiles can survive in conditions hostile to most other life forms. Examples include hyperthermophiles in hot springs and hydrothermal vents, halophiles in extremely salty environments like salt lakes, acidophiles in highly acidic environments, and methanogens in oxygen-free environments like deep soil or sediments.

Challenges to Explaining the Origin of Cells

• A challenge to explaining the spontaneous origins of cells is the inability to directly observe ancient events.

Stromatolites

• A stromatolite is a layered structure formed by photosynthetic bacteria.

Age of Earth

• The approximate age of Earth is 4.5 billion years.

Bacterial DNA Exchange

• Bacterial pili are used to exchange DNA between cells.

Function of Prokaryotic Cell Wall

• The primary function of the prokaryotic cell wall is to prevent the cell from bursting.
• The cell wall is crucial for prokaryotes because it provides structural support, maintains cell shape, and prevents the cell from bursting due to osmotic pressure differences between the inside and outside of the cell, offering protection against physical damage and some chemical threats.

Where to Find Anaerobes

• Obligate anaerobes are found in deep soil without oxygen.

Forms of Estimating When Life Began on Earth

• Literary evidence is NOT a form of evidence used to estimate when life began on Earth.

Role of RNA in Early Cells

• According to the RNA world hypothesis, RNA acted as both genetic material and catalyst in early cells.

Prokaryotic Ribosomes

• The size designation for prokaryotic ribosomes is 70S.

Characteristics of Archaea

• The ability to perform methanogenesis is a characteristic of archaea but NOT bacteria.

Other Structures

• Flagella are long, whip-like protein structures that enable cell movement by rotating and propelling the bacterium. Pili are shorter, hair-like protein structures used for adherence to surfaces or other cells, and some specialized pili (sex pili) facilitate DNA transfer between bacteria through conjugation. Photoautotrophic archaea use light as their energy source (though they use pigments other than chlorophyll and don't produce oxygen), while chemoautotrophic archaea obtain energy by oxidizing inorganic chemicals such as hydrogen sulfide, ferrous iron, molecular hydrogen, or ammonia. Both types use CO2 as their carbon source.

Early Earth

• Reducing atmosphere with gases like ammonia (NH3), hydrogen (H2), and methane (CH4)
• High temperatures from asteroid collisions and planetary formation
• Intense UV radiation reaching the surface due to lack of an ozone layer
• Volcanic activity releasing gases and constant asteroid bombardment

Gut Microbiotas

• The gut microbiota contributes to human health by producing vitamins (K and B vitamins) and amino acids
• Training and supporting the immune system
• Strengthening the gut barrier
• Preventing invasion by harmful microbes
• Metabolizing drugs and detoxifying harmful substances
• Producing important molecules that communicate with the brain and other organs
• Influencing gut movement and function