The Origin Of Heredity

Chapter 10 provides a detailed explanation of how hereditary information affects the phenotype of cells. Recall that the hereditary information contained in a DNA molecule is first transcribed into an RNA message, and then the RNA message is translated into a protein, as shown in Figure 14-8. Thus, DNA serves as the template for RNA, which in turn serves as the template for specific proteins.

In recent years, scientists have taken a closer look at the DNA-RNA-protein sequence. Why is RNA necessary for this process? Why doesn't DNA, which is a template itself, carry out protein synthesis directly? The clues to a more complete understanding of RNA function may be found in its structure. RNA molecules take on a greater variety of shapes than DNA molecules do. An example is the unique shape of transfer RNA, shown in Figure 14-8. These shapes are dictated by hydrogen bonds between particular nucleotides in an RNA molecule, much as the shapes of proteins depend on hydrogen bonds between particular amino acids. These questions and observations led to the speculation that some RNA molecules might actually behave like proteins and catalyze chemical reactions.


• Explain the importance of the chemistry of RNA in relation to the origin of life.

• List three inferred characteristics that describe the first forms of cellular life on Earth.

• Compare the two types of autotrophy used by early cells.

• Relate the development of photosynthesis to the development of aerobic respiration in early cells.

• Explain the theory of endosymbiosis.

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