Let's focus in this chapter on the structure of DNA--what DNA is . In the next, I'll cover how DNA functions--what it does . Structure and function work hand-in-hand. The old saw is "structure determines function." That's a bit of an oversimplification, but it is clearly the case with respect to DNA. In fact, when the structure of DNA was discovered by James Watson and Francis Crick (with key x-ray crystallographic data supplied by Rosalind Franklin), they knew immediately ho

Having been just reviewed the cell cycle we now focus on the fourth step of that process, mitosis, where the two genomes are pulled into their new cells. This is an amazing feat of cellular choreography that I liken to a line dance. Let's take a quick look at the entire mitosis process from start to finish before covering each step in more detail. The entry point is the very end of interphase--that is, the combination of phases G1, S, and G2. The genome has been copied and al

Most of the time, most of your cells are simply doing their jobs. Neurons are sending electrochemical signals. Cardiac muscle cells are contracting rhythmically. Rod and cone cells are detecting the text you're in the process of reading. At the same time, though, your body is constantly renewing itself at the cellular level.   It is estimated that about 330 billion cells in an adult human body are replaced every day (1). That's a big number. But even that represents less tha

In the last chapter, I likened a human cell to a factory and then extended the analogy to the major components of a cell. In this chapter, I'll be more direct and literal in describing the cell's contents. Again, what I'll be describing are the contents of a generic human cell. I'll proceed from larger to smaller cell components, starting with organelles . And I won't go over organelles in detail since I already introduced them them in the last chapter. Then I'll introduce ma

Let's first get some perspective. Proteins account for about 50% of the cell's dry weight. That's much more than DNA, which accounts for about 1-2%. It's also more than RNA, which accounts for approximately 20%. All of these figures depend on cell type and growth state. But--big picture--about half of the cell is proteins. But it isn't just the quantity that makes them important. Proteins are the workhorses of the cell. RNAs play key functional roles in the cell, too. But eve

Analogies are ubiquitous in molecular biology. Traditionally, two analogies have been used to describe the cell: the cell as a factory and the cell as a city . Some will say these analogies are overused. I disagree. They are heavily used. But that's because they are effective. We’ll use the factory analogy.   Think about a factory. It's a physical facility that brings in raw materials and uses human workers, tools and technologies, and energy to produce a finished product. F

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

I've always 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 seemingly spontaneously from inanimate matter randomly crashing around. How can molecular precision arise from apparent molecular randomness? ​In this book, I try to paint a clear picture of the cell

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