A.2.1 Origins of Cells

Based on the 3rd edition biology textbook written by C.J. Clegg, Andrew Davis, Christopher Talbot

greenhouse gas

the heating caused by the atmosphere on Earth’s surface because certain atmospheric gases absorb and emit infrared radiation

greenhouse effect

process in which greenhouse gases trap outgoing long-wave radiation from the Earth, causing the planet to be warmer than it would otherwise be

ex: methane, carbon dioxide

early atmosphere of Earth

95% carbon dioxide

4% water vapor

1% nitrogen, ammonia, methane

average surface temperature 400C

today’s atmosphere of Earth

78% nitrogen

21% oxygen

1% carbon dioxide, water vapor, ammonia, methane

average surface temperature 20C

primordial (prebiotic) soup hypothesis

UV radiation led to the formation of the first biological molecules

UV radiation broke bonds of molecules, leading to small, highly reactive atoms that formed new molecules (amino acids, peptides, ribose, nucleobases, fatty acids, nucleotides, oligonucleotides)

found by Alexander Oparin 1924

common features of cells

1. a stable, partially permeable membrane that surrounds cell components

2. genetic material that can be passed on when new cells are formed, and which controls the function and behavior of cells

3. metabolic processes hat allow energy generation enabling growth, self-maintenance, and reproduction

formation of living cells from non-living materials

1. synthesis of simple organic molecules (sugars, amino acids)

2. assembly of these molecules into polymers

3. development of self-replicating molecules (nucleic acids)

4. retention of molecules within membranous sacs, so that an internal chemistry developed differs from the surrounding environment

protocell first theory

a cell-like entity that had metabolism but lacked a fully developed genetic system

it evolved over time to have a full structure of nucleic acids, such as RNA

was surrounded by lipids that trapped pre-biotic “soup”

SL Miller and HC Urey experiment

used a reaction vessel in which an atmosphere could be recreated

shot electric sparks through the early Earth atmosphere, causing molecules to break down and form new ones

amino acids could’ve been formed like that

not good enough as it wasn’t an actual early Earth atmosphere and they didn’t use UV radiation

RNA world hypothesis

a hypothesis that proposes that the earliest life forms (protocells) may have used RNA alone for the storage of genetic material or forming of proteins

Last Universal Common Ancestor (LUCA)

a hypothesis of the last common ancestral cell from which the three domains of life, the Bacteria, the Archaea, and the Eukarya originated from

probably lived in deep-sea hydrothermal vents

had a lipid bilayer and possessed the genetic code and ribosomes which allowed duplication, mutation, and protein synthesis

was anaerobic, CO2 to glucose, H2 as energy, N2 for amino acids, thermophilic - lived in high temperatures

extremophile

an organism that lives in conditions of extreme temperature, acidity, alkalinity, salinity, pressure, or chemical concentration

autotrophic

synthesizing glucose from simple inorganic substances using an external source of energy