Origin of cells

• The origin of cells is a topic of interest in the field of biology.
• Cells are the smallest units of self-sustaining life.
• The cell theory states that all organisms are composed of at least one cell, all cells come from pre-existing cells, and all cells perform metabolism, maintain homeostasis, respond to stimuli, are capable of reproduction, grow and develop, and contain genetic information (in the form of DNA).
• The likelihood of other forms of life having evolved but becoming extinct due to competition from the last universal common ancestor (LUCA) and descendants of LUCA should be included.
• Students should develop an appreciation of the immense length of time over which life has been evolving on Earth.
• Fossilized evidence of life from ancient seafloor hydrothermal vent precipitates and evidence of conserved sequences from genomic analysis provide evidence for the evolution of the last universal common ancestor in the vicinity of hydrothermal vents.
• Viruses do have genetic material (DNA or RNA), however they do not possess most of the characteristics of life.
• Viruses do not have cells which carry out metabolism and homeostasis.
• Viruses cannot respond to stimuli, and they do not grow.
• Viruses are not capable of reproducing themselves, they are replicated by host cells.
• Most scientists do not consider viruses to be alive due to their lack of certain characteristics of life.
• Cell membranes are formed of phospholipid bilayers, and phospholipids are amphipathic, with hydrophilic phosphate heads, and hydrophobic fatty acid tails.
• Fatty acids have formed spontaneously in experiments similar to Miller and Urey’s experiment, and fatty acids spontaneously coalesce to form spherical bilayers (vesicles) when mixed with water.
• Experiments similar to Miller and Urey’s show that the building blocks of life, such as proteins and nucleotides can form from these chemicals.
• RNA is presumed to be the first genetic material because it can store genetic information, it is capable of self-replication, and it can catalyze reactions.
• Cell metabolism requires the separation of the cytoplasm from the external environment, and cell membranes serve this function in modern cells.
• It has been hypothesized that the first genetic material was trapped within a phospholipid vesicle forming a protocell.
• Ribozymes (RNA molecules) in the ribosome catalyze the formation of peptide bonds during protein synthesis.
• Evidence suggests that LUCA evolved in the vicinity of hydrothermal vents, and hydrothermal vents are rich in organic compounds, such as methane, carbon dioxide, and hydrogen.
• Miller and Urey carried out an experiment to test Haldane and Oparin’s hypothesis that the macromolecules of life could have spontaneously generated on a prebiotic Earth.
• Fossils of cyanobacteria have been discovered from ancient seafloor hydrothermal vent precipitates, and an analysis of genes common to all the three domains of life has identified genes that are highly conserved, some of which are involved in thermophilic metabolism, suggesting that LUCA may have evolved in a high temperature environment such as hydrothermal vents.
• Miller and Urey’s experiment modelled prebiotic Earth and its atmosphere, demonstrated that molecules such as amino acids can be generated spontaneously under certain conditions, and the design of the experiment allows it to be replicated by other scientists.
• The last universal common ancestor (LUCA) is the most recent common ancestor for all organisms on Earth, and there may have been other forms of life at the same time as LUCA, but these forms of life became extinct as LUCA and its descendents outcompeted them.
• The simulation could not account for all conditions on the prebiotic Earth.
• There remains debate on the actual atmosphere of prebiotic Earth.
• The experiment did not produce all of the organic molecules required for life.
• The fact that all organisms share the same genetic code strongly suggests that all organisms have evolved from LUCA.
• Darwin's Tree of Life is a concept in evolutionary biology.
• The oldest fossils of cells (of cyanobacteria) are approximately 3.5 billion years old.
• Molecular clocks: Comparing the number of mutations in genes between species allows scientists to estimate when the two species diverged into separate species.
• LUCA, or the last universal common ancestor, is the most recent common ancestor of all living organisms.
• Pre-Biotic refers to the period before the emergence of life on Earth.
• The Earth is 4.6 Billion Years Old!
• Domains are the fundamental units of life.
• Vesicle refers to a small container.
• Eubacteria, Archaea, and Eukarya are the three domains of life.
• All living things share a number of genes, which are assumed to have been inherited from LUCA.
• Scientists have used this technique to estimate that LUCA existed approximately 4 billion years ago.
• Hydrothermal Vent is a geological feature.
• There are no fossil remains for the last universal common ancestor (LUCA).