Читать книгу Astrobiology - Charles S. Cockell - Страница 134

At the cellular level, life is complex. Nevertheless, we can identify cell types, and we can broadly recognize certain features about them that they all share. The basic biochemical structure of cell membranes, made of amphiphilic lipids, is common to all cellular life, although there are different types of membranes in different organisms. Similarly, the reading of the genetic code, from DNA to RNA to protein, is common to life on Earth. The genetic code is exquisitely evolved for its role in storing information, yet we also have seen how it contains redundancy in the amino acids for which it codes (the degeneracy of the genetic code). Eukaryotic cells are more complex than prokaryotic cells, but exhibit some of the same fundamental structures. Despite our view of them as “simple,” prokaryotes exhibit some remarkably complex behaviors such as movement and quorum sensing. We have seen how prokaryotes exhibit some rudimentary forms of multicellular behavior, which invites important questions about how differentiated multicelled structures evolved. Life on Earth exhibits a vast variety of cellular structures and shapes, and it interacts with non-cellular structures such as viruses. A question that emerges across all these types of cellular structures is: Where do they get their energy to grow and reproduce? This is the subject of the next chapter.