In the last chapter, we focused on the genetic code--how DNA stores instructions for building proteins. Now we turn to how that code is read. The process is quite orderly. Information flows from DNA to RNA and then to protein, in a sequence known as the central dogma of molecular biology. This flow is how the cell turns stored information into proteins that do things. The central dogma was put forth in 1958 by James Watson of Watson and Crick fame (discoverers of the structu

The last chapter covered DNA's structure: what it is. In this chapter, we shift our focus to function: what DNA does—or, more exactly, how it works. The Genetic Code If we were to walk down a stretch of double stranded DNA we could announce the letters on one or the other of the strands as we passed: "ATGTCGGATAGATGA", for example. A code is contained in these 15 letters. The primary purpose of the code is to make proteins --but DNA does so indirectly, using mRNA as an inter

In this chapter, we focus on what DNA is--its structure--before turning to what it does. It is said that structure determines function and DNA embodies this. When the structure of DNA was discerned by James Watson and Francis Crick (with key x-ray crystallographic data supplied by Rosalind Franklin), they understood immediately how it would function. In their seminal 1953 article in the scientific journal Nature , they wrote (cheekily): " It has not escaped our notice that th

A typical human cell contains tens of millions of protein molecules, each carrying out a specific task. Some proteins cut DNA. Others build new molecules, transport cargo, or send signals from one part of the cell to another. Many are literal molecular machines—motors, pumps, switches, and clamps—operating at a scale far too small to see but performing the work that keeps the cell alive. To get some perspective, proteins account for about 50% of the cell's dry weight. That's

Imagine shrinking down until you're inside a human cell. If all the molecules and ions were to slow down from their rapid random movement, would you see? First you'd be struck by the large, membrane-bound compartments all around you--the organelles. After that, you might notice an enormous variety of molecular machines doing different jobs both funcvtionaland structural. These are the macromolecules. And finally, there will be countless smaller molecules and ions crashing abo

Two analogies are commonly used to describe cells: the cell as a factory and the cell as a city. In this chapter, we’ll use the factory analogy.   Think about a factory. It brings in raw materials and uses workers, tools, and energy to produce a product or service. To do that, it needs power, an assembly line, instructions, storage facilities, and systems for waste disposal. Cells have analogs for all these.   Structure Factories are enclosed buildings. Cells have a cell memb

Humans have known of the existence of cell-like structures since the 1600s when early microscopists used their instruments to look at plant and animal tissues. They found that the plant tissues were made up of many small compartments. (Animal cells are harder to visualize largely because they have no hard cell walls.) They called them “cells” but didn't conceptualize them as individual biological units. It wasn’t until the mid-1800s that a coherent theory of the cell—not su

Since college, I've been amazed at life at the cellular level. Inside your 50 trillion or so cells, untold numbers of molecular machines are performing complex tasks with incredible precision. Yet nobody is running the show. Everything that takes place there--in fact, life itself--arises spontaneously from inanimate matter randomly crashing around. How can precision arise from randomness? ​In this book, I try to paint a clear picture of the cellular world that underscores thi

Humankind has always reflected on the mystery of life. Rocks fall. Clouds float. Water flows. But living things have a whole other set of capabilities. They move of their own agency. They respond to their environment. They repair themselves. They metabolize food. They reproduce. These are hallmarks of all living organisms. What enables organisms to do all these things? How do living things “work?” This book attempts to paint a picture of what life looks like and how it works