Chapter Introduction

1: Evolution, Science, and Molecular Biology

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  • 1.1 The Evolution of Life on Earth

  • 1.2 How Scientists Do Science

MOMENT OF DISCOVERY

Jack Szostak

A big question in the origin of life concerns how primitive cells might have evolved. My own approach to this question involved lots of discussions with Irene Chen and others in my lab about how lipid vesicles containing RNA, which might mimic a simple self-replicating life form, could be capable of dividing. In other words, as the amount of genetic material (here, RNA) increased by making more copies of itself, how would the increased RNA content affect the physical properties of the vesicle? We envisioned that osmotic pressure might make vesicles grow by extracting lipids from neighboring vesicles, ultimately leading to division by rupture and resealing. This idea seemed pretty far out, though, until Irene began doing experiments with vesicles containing lipids bearing fluorescent dyes. We could encapsulate RNA inside the vesicles and watch the vesicles change in size (or not) under different conditions by following the level of fluorescence as a function of vesicle surface area. Irene found that empty vesicles or vesicles “swollen” with RNA were stable over time, but when she mixed them together, the swollen vesicles started to grow by stealing lipid molecules from neighboring empty vesicles! So the system worked exactly as we had imagined, demonstrating that vesicle growth and division is a process that can occur spontaneously.

More recently, we found that vesicles loaded with RNA can also take up nucleotides (the building blocks of RNA and DNA) from the environment, disproving an old idea that it would be hard for primitive cells to survive by taking up small molecules, including negatively charged nucleotides, from their surroundings. It has been very exciting to find that each potential roadblock to primitive cellular replication that we have explored so far can be overcome, often without requiring specialized catalysts or input energy.

—Jack Szostak, on his discovery of self-dividing vesicles that mimic growing cells

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Born in the second half of the twentieth century, molecular biology has only recently come of age. Broadly speaking, molecular biology is the study of essential cellular macromolecules, including DNA, RNA, and proteins, and the biological pathways between them. Over the decades, molecular biology has become firmly associated with the structure, function, and regulation of information pathways at the molecular level. All of the processes required to reliably pass genetic information from one generation to another and from DNA to RNA to protein are included in this area of study. Of the requirements for life, it is the information in our genetic material that links all organisms to each other and documents their intertwined history. The biological information pathways that maintain, use, and transmit that information are the focus of this book.

Molecular biology may have a relatively short history, but its impact on the human experience is already considerable. Medicine, modern agriculture, forensic science, and many other endeavors rely on technologies developed by molecular biologists. Our current understanding of information pathways has given rise to diagnostic tests for genetic diseases, forensic DNA analysis, crops with improved yields and resistance to disease, new cancer therapies, an unprecedented ability to track pandemics, new wastewater treatment methods, new approaches to the generation of energy, and much more. Many of these advances are chronicled throughout this textbook.

This first chapter introduces three of the most important themes that link the book’s topics. The first theme concerns the two key requirements for life: biological information, the genetic instructions that shape every living cell and virus, and catalysis, a capacity to accelerate critical molecular processes. Molecular biology deals with both, and much of the discipline focuses on the interplay between information-containing polymers (nucleic acids and proteins) and the enzymes that catalyze and regulate their synthesis, modification, function, and degradation.

The second theme is evolution. Many of the processes we will consider can be traced back billions of years, and a few can be traced to the last universal common ancestor. Genetic information is a kind of molecular clock that can help define ancestral relationships among species. Shared information pathways connect humans to every other living organism on Earth and to all the organisms that came before.

The third theme in this book is how we look at molecular biology as a scientific endeavor. Any scientific discipline is a construct not only of the knowledge it has generated but also of the human processes behind that knowledge. Molecular biology has both an inspirational history and a promising future, to be forged by contributors as yet unnamed. Breakthroughs rely on more than technology and ideas: they require an understanding of the scientific process and are informed by the struggles of the past.