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    How Life Works: The Inside Word from a Biochemist
    How Life Works: The Inside Word from a Biochemist
    How Life Works: The Inside Word from a Biochemist
    Ebook187 pages2 hours

    How Life Works: The Inside Word from a Biochemist

    By William Elliott and Daphne C. Elliott

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    About this ebook

    Complete with colour illustrations and written in a conversational style, biochemist William Elliott unravels the mystery of life while revealing its majesty. How do chemical reactions occur? How do genes hold information? Why do our bodies age? What happens when someone gets cancer? How Life Works provides the inside word for those who are curious about the workings of the microscopic world inside us.

    Biochemistry not only explains what DNA is and how it forms the blueprint for who you are, it also explains how the food you eat is broken down, supplying the energy to run a marathon. It shows the intricate structures of proteins and describes their amazing functions. With millions of interactions and reactions all taking place in accord, biochemistry is the science of how life works.

    LanguageEnglish
    PublisherCSIRO PUBLISHING
    Release dateSep 1, 2015
    ISBN9781486300495
    How Life Works: The Inside Word from a Biochemist

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      Book preview

      How Life Works - William Elliott

      1

      The fantastic nature of matter

      In a book whose main aim, as outlined in the Preface, is to describe the fundamental nature of life, you could reasonably ask why it should start with an account of the atomic nature of matter, meaning anything in the universe that occupies space.

      Everything is made of atoms, including all life forms. The existence of the phenomenon we know as life is due to the nature and properties of atoms, so this is a good place to start in understanding what life is. A bonus is that the story of how atoms came to exist on Earth is one of the most exciting in science.

      The name ‘atom’ derives from the Greek word atomos, meaning indivisible. The Greek philosopher Democritus arrived at the concept that everything – all solids, liquids and gases – is made of minute particles that cannot be divided into smaller units. In other words, if you could cut up any matter into smaller and smaller pieces you would ultimately arrive at particles that you could not subdivide any further. Atoms were envisaged more or less as hard solid little balls. Although the concept of atoms has been around for so long, it is only in the last two centuries that they have been scientifically studied, and only in the last two decades that anyone has actually seen them as images using new microscopic techniques. They are indescribably small – the number in a few drops of water is approximately 10 followed by 20 zeros (1021).

      Of the 92 naturally different atoms in the universe, only around 25 are found in your body, some in very small amounts. The four elements hydrogen, carbon, nitrogen and oxygen make up about 99% of the total number. The term ‘element’ is used to refer to a substance that is made from one type of atom and cannot be broken down by chemical means. The atoms in living organisms are the same as the corresponding ones in non-living matter. A carbon atom in your body is the same as a carbon atom in chimney soot or anywhere else in the universe, and the same applies to all atoms. So what then is the nature of life? What makes the difference between non-living and living matter?

      We can talk about life as a single process. This may seem surprising in view of the vast variations found in life forms. The French Nobel prizewinner Jacques Monod famously expressed it as ‘what holds for Escherichia coli is true for an elephant’. He meant that the basic chemistry of the microscopic bacterial cell E. coli, which lives in the human gut in countless numbers, is much the same as the chemistry of cells in an elephant. The similarities far outweigh the differences.

      Life is basically a chemical process. And this is true for all living organisms. The reason for this is that there was a single origin of life from which all life has developed over approximately 3 billion years.

      The salient feature of life is that it reproduces itself. The first form of life must have been a relatively simple self-reproducing collection of atoms on the primeval Earth, and since then life has been handed down from generation to generation. To do this a system of passing on information had to be devised which determines that the offspring resembles the parents. In other words, there had to be a genetic system.

      The basic mechanism of the genetic system is the same in an E. coli cell as in a human, a whale, a tree, an insect, or any life form you care to nominate. There are superficial differences in detail between the process in E. coli and higher forms, but these do not affect the essentials. It seems that life became locked into the method of passing on genetic information to offspring at a very early stage of evolution.

      The process of evolution has also superimposed variations on this basis of life that enable organisms to exploit environmental niches. Plants, for example, developed the ability to use sunlight as an energy source; birds adapted to the air and whales to the sea, but it has not changed the basis of life common to all.

      There are also fundamental laws of nature that life had to conform to; once again the remarkable solutions to these problems are much the same in all life. We will come to discuss these in subsequent chapters.

      The living unit of organisms is the cell

      Living cells are, with the inevitable rare exceptions, microscopic structures surrounded by a membrane (Fig. 2.2). In your body there are many trillions of cells. The E. coli cell is about 1000 times smaller in volume than animal and plant cells.

      Why are cells so small? They have to communicate chemically with the outside world through the membrane. There are mechanisms for transporting chemicals in and out of the cell and for conveying signals into it. For example most chemical messengers such as insulin do not enter cells but deliver a signal to it via receptors in the membrane, which act like aerials. What has this got to do with cell size? There has to be an adequate area of membrane to service the needs of the cell. Minute cells satisfy this requirement because they have a lot of surface in proportion to their volume, but if you increase cell size the volume increases much more rapidly than does its surface area. You quickly arrive at the point at which the membrane area is inadequate to support the needs of the cell. So living cells have to be tiny.

      A bacterium like E. coli is free living, but to build larger organisms cells are aggregated into more complex organisms. This requires a regulatory system to coordinate the activities of individual cells to the needs of the organism as a whole. In an animal such as a human this becomes very complex indeed. The number of human cells that have to be kept in step with one another vastly outnumbers the whole of the population on Earth, so you can see this is no small problem. Cancer is the result of a cell no longer observing the regulatory rules and going its own way.

      So, a living cell is a chemical device. Obviously many will say that life is more than chemistry, but I am talking about the process of life and, whatever views are held, there has to be a mechanism. To most people without any training in chemistry this statement will not be meaningful, but with a simple knowledge of atoms it is possible to understand the nature of life at a profound level.

      Biology is dependent on chemistry

      Chemistry is essentially a description of how atoms react with one another, and from this life can be seen as the outcome of a large number of chemical reactions occurring in an organised manner in living cells. Here is the basis for the connection between biology and chemistry.

      In the case of humans there are somewhere of the order of tens of thousands of different chemical reactions. This involves rough estimates but the number is very large. Behind these chemical reactions there are several fundamental problems that life had to solve to conform to the natural laws of the universe. What these problems are and the way in which they were solved is mainly what this book is about.

      The thousands of individual reactions in life are details which do not have to be described for you to understand the principles of the living process. Leaving these aside, we are left with the big picture of life – the major concepts that determine the nature of life and its relationship to the laws of the universe.

      The first step is to look at the nature and properties of atoms. A good point to start is to discuss where atoms and the universe came from in the first place.

      The Big Bang

      Astrophysicists have discovered that 13.7 billion years ago there were no atoms and no universe. At that date the universe came into existence with an indescribable explosion. The physicist Fred Hoyle, in Cambridge, argued tenaciously for an alternative theory that the universe has always existed and always will exist, known as the steady-state universe. He dismissed the explosion theory, describing it, rather derisively, as the ‘Big Bang’, but evidence rapidly accumulated that the explosion theory is correct. The term Big Bang summarised it so well that it was adopted by its supporters and is now used by everyone.

      To return to the Big Bang, what was it that exploded? No one knows, but it was from a source of infinite density and energy content. It contained all the components and energy of the present entire universe. If you reflect that there are hundreds of billions of galaxies in the universe, each with hundreds of billions of stars, it was some condensation! What was there before this ‘thing’? Physicists tell us that the question is invalid because there was no ‘before’, since Einstein’s relativity theory shows that time was created at the Big Bang. So was space. The explosion of the Big Bang is not to be thought of as ejecting things into space but as the creation and expansion of space. The space between objects expanded, so that in the course of the explosion they became increasingly separated as the universe

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