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Across all forms of life, there are several shared and conserved processes and features that provide strong evidence of a common evolutionary origin. In this section, we will explore some of these fundamental traits and processes that support the theory of a common ancestor for all organisms.
DNA and RNA
All organisms use DNA and RNA as the genetic material that codes for proteins essential for life. DNA across all organisms has the same structure and consists of the same four nucleotides. It is highly unlikely that a structure of this level of complexity would independently form in different groups of organisms.
Ribosomes
All cells contain ribosomes which facilitate RNA translation and protein synthesis. Ribosomes are complex structures and their presence in all cells suggests a common ancestor. Other cellular components, such as the cytoplasm and cell membranes, are also present across all groups of organisms.
Genetic Code
Not only is the use of DNA and RNA to hold genetic code consistent for all organisms but there are also specific sequences of this code that remain conserved across all life. Genes within any organism's genetic code are expressed through the processes of DNA transcription and translation, which will be covered in detail in Unit 6. These commonalities indicate that such genetic information was likely inherited from a common organism.
Metabolic Pathways
Many cellular pathways, such as cellular respiration, are highly conserved across all types of life. These pathways contain the essential processes that govern how life functions. Given that they are similar or the same in most organisms, these pathways were likely derived from a common ancestor.
