Life arose on Earth about 3.5 billion years ago from the spontaneous assembly of small organic molecules. Over millions of years, these simple molecules acquired the ability to interact and ultimately developed mechanisms of self-replication. These mechanisms became more elaborate as evolutionary forces brought their influence to bear. The first true cells arose when DNA, RNA, and proteins became contained within a boundary, the plasma membrane. These first unicellular organisms acquired the ability to interact. Multicellularity endowed these early organisms with the ability to organize into ever more complicated structures, ultimately giving rise to the explosion in biodiversity we see today. Cells, proteins, and genes are so interconnected that it would be impossible to consider only one level of organization. Thus, we begin our chapter with a discussion of the evolution of cell structure. We then consider the structure-function relationships between nucleic acids and proteins. We next describe cellular processes fundamental to cell survival, including gene regulation and cell proliferation. We also explore the process of cell death. We end our chapter by discussing multicellularity and cell communication.
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