Study GuideBiology–The Origin and Evolution of Life1. Origin of CellsThe appearance of the first cells marked the beginning of life on Earth. However, cells did not appearsuddenly. Before cells could exist, smaller organic molecules had to join together to form larger, morecomplex molecules calledpolymers.Polymers are large molecules made from smaller building blocks. Important examples includeproteinsandpolysaccharides, both of which are essential for life.1.1Formation of Early Organic MoleculesIn the 1950s, scientistSidney Foxconducted experiments to study how life might have begun. Heplaced amino acids—the building blocks of proteins—under conditions similar to those of early Earth.Fox discovered that amino acids could naturally join together to form polymers known asproteinoids.These proteinoids showed enzyme-like behavior, meaning they were able to speed up chemicalreactions. This finding suggested that simple molecules could organize themselves into morecomplex, life-like structures.1.2The Possible Role of RNAMore recent research has focused onRNAas a key molecule in the origin of life. Scientists havefound that RNA can direct the formation of new RNA molecules and even help produce DNA.Since DNA carries the genetic instructions for making proteins, it is possible that DNA formed later asa result of RNA activity. Once DNA existed, it could have guided protein production, leading toincreasingly complex biological systems.1.3The Search for the First CellFor a true cell to exist, it needs amembraneto hold its contents together and separate the internalenvironment from the outside world. Earlier scientists believed that simple membranous dropletsformed naturally and became the first cells. These structures were calledprotocells.Preview Mode
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