Origin of Cells

Pre-biotic Earth

the period before life existed on earth, characterized by harsh environmental conditions and a lack of biological processes

Reducing Atmosphere

• refers to an environment with low levels of oxygen and high levels of hydrogen and other gases

  • CH4, water vapour, CO2, ammonia

• believed to have existed in Early Earth, facilitating the formation of organic compounds

Energy Sources on Early Earth

These primary energy sources drove chemical reactions of Early Earth:

1. Solar Radiation(UV light)

2. Geothermal Heat(volcanic activity)

3. Electrical Energy(lightning)

Hydrothermal Vents

underwater fissures that released heated, mineral-rich water, providing unique environments for chemical reactions

Specialized Environments & Formations

Formations

1. Amino acids(building blocks of proteins)

2. Nucleotides(building blocks of DNA)

3. Simple Sugars

Environments

• environments provided both the raw materials and energy needed for chemical synthesis

1. Volcanic Activity

2. Tidal Pools

3. Hydrothermal Vents

Theories on the Origin of Cells

1. Abiogenesis: the idea that life arose naturally from non-living matter

2. Panspermia: the hypothesis that life originated elsewhere in the universe and was brought to Earth

3. Creationism: the belief that life was created by a supernatural entity

Key Requirements for Origin of Life

1. Organic Molecules: building blocks of life, such as amino acids and nucleotides

2. Energy Source: To drive chemical reactions

3. Catalysts: to speed up and control reactions

4. Compartmentalization: to separate and protect chemical processes

The Miller-Urey Experiment

• Miller and Urey conducted a groundbreaking experiment to test the hypothesis of abiogenesis

  • simulated Earth conditions by creating an atmosphere containing simple gases(CH4, NH3, H2O, H2)

  • amino acids formed

Role of RNA

1. Information Storage: Like DNA, RNA can store genetic information

2. Catalytic Activity: Some RNA molecules can catalyze chemical reactions(ribozymes)

3. Self-Replication: RNA can potentially replicate itself under certain conditions

Ribozymes

An RNA molecule capable of catalyzing specific biochemical reactions, similar to the action of protein enzymes

Self-Assembly of Biological Structures

• Biological structures can form spontaneously through a process called self-assembly

  1. Phospholipid Bilayers: form the basic structure of cell membranes

  2. Microspheres: spherical structures formed by proteins and other polymers

  3. Coacervates: droplets formed by the aggregation of organic molecules

Importance of Compartmentalization

• Compartmentalization is a fundamental feature of living cells

  1. Isolation: separating different chemical reactions

  2. Protection: shielding fragile molecules from the environment

  3. Concentration: Increasing the likelihood of reactions by increasing the concentration of reactants

Protocell

A simple, prebiotic structure resembling a cell, consisting of a membrane enclosed compartment containing organic molcules

Role of Hydrothermal Vents

1. Rich Chemical Environment: providing essential elements and compounds

2. Thermal Gradients: Offering a range of temperatures for different reactions

3. Natural Catalysts: Minerals that can facilitate chemical reactions

Challenges in Studying: Origin of Life

1. Time Scale: events occurred billions of years ago

2. Complexity: many interconnected processes were involved

3. Lack of Direct Evidence: no physical traces of the first life forms remain

Compartmentalization

The separation of different environments or processes within a system, allowing for specialized functions to occur simultaneously without interference

Amphipathic Molecules

• molecules that posses both a hydrophillic(water-attracting) and hydrophobic(water-repelling) region

• crucial for the formation of bilayers, as they can arrange themselves into bilayers, creating compartments

• allows for the regulation of material exchange and the establishment of a controlled environment for chemical reactions

Key Processes w/in Vesicles

1. Polymer Formation: conditions inside vesicles supported the assembly of polymers(e.g. proteins & nucleic acids)

2. Replication of Genetic Material: Self-replicating molecules like RNA could begin copying themselves with the vesicles, ensure the continuity of information

RNA World Hypothesis

a scientific theory that suggests RNA served as both the genetic material(storing info) and a catalyst(facilitating chemical reactions) before the evolution of DNA and proteins

Genetic Code

A system that translates DNA instructions into proteins, the essential building blocks of life

Origin of Cells Theories

1. Protocell-first theory: proposes that a cell-like compartment capable of some basic metabolic functions arose spontaneously

2. Gene-First Theory: spontaneous development of a nucleic acid(most likely RNA) that could self-replicate

3. Metabolism-First Theory: proposes that life originated as a system of chemical reactions capable of sustaining itself