Chown What a Wonderful World

One Man's Attempt to Explain the Big Stuff
Main
ISBN: 978-0-571-27842-8
Verlag: Faber & Faber
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 300 Seiten

With wit, colour and clarity, What A Wonderful World quickly and painlessly brings us up to speed on how the world of the 21st century works. From economics to physics and biology to philosophy, Marcus Chown explains the complex forces that shape our universe. Why do we breathe? What is money? How does the brain work? Why did life invent sex? Does time really exist? How does capitalism work - or not, as the case may be? Where do mountains come from? How do computers work? How did humans get to dominate the Earth? Why is there something rather than nothing? In What a Wonderful World, Marcus Chown, bestselling author of Quantum Theory Cannot Hurt You and the Solar System app, uses his vast scientific knowledge and deep understanding of extremely complex processes to answer simple questions about the workings of our everyday lives. Lucid, witty and hugely entertaining, it explains the basics of our essential existence, stopping along the way to show us why the Atlantic is widening by a thumbs' length each year, how money permits trade to time travel why the crucial advantage humans had over Neanderthals was sewing and why we are all living in a giant hologram.

Marcus Chown is an award-winning science writer and broadcaster. Formerly a radio astronomer at the California Institute of Technology in Pasadena, he is now cosmology consultant for the New Scientist. His acclaimed books include What a Wonderful World, Quantum Theory Cannot Hurt You, We Need to Talk about Kelvin and The Ascent of Gravity(Sunday Times Science Book of the Year 2017). He is also the author of Solar System for iPad, which won The Bookseller 2011 Digital Innovation of the Year. www.marcuschown.com @marcuschown

Autoren/Hrsg.

Chown, Marcus

Leseproben

1:

I AM A GALAXY

A good case can be made for our non-existence as entities.

LEWIS THOMAS

There’s someone in my head and it’s not me.

PINK FLOYD

I think I am me. But I am not. I am a galaxy. In fact, I am a thousand galaxies. There are more cells in my body than there are stars in a thousand Milky Ways. And, of all those myriad cells, not a single one knows who I am or cares. am not even writing this. The thought was actually a bunch of brain cells – neurons – sending electrical signals down my spinal cord to another bunch of cells in the muscles of my hand.1

Everything I do is the result of the coordinated action of untold trillions upon trillions of cells. ‘I like to think my cells work in interest, that each breath they draw for , but perhaps it is who walk through a park in the early morning, sensing my senses, listening to my music, thinking my thoughts,’ wrote American biologist Lewis Thomas.2

The first step on the road to discovering that each and every one of us is a super-colony of cells was the discovery of the cell itself. Credit for this goes to Dutch linen merchant Antonie van Leeuwenhoek. Aided by a tiny magnifying glass he had adapted from one used to check the fibre density of fabrics, he became the first person in history to a living cell. In a letter published in April 1673 in the of the Royal Society of London, van Leeuwenhoek wrote, ‘I have observ’d taking some blood out of my hand that it consists of small round globuls.’

The term ‘cell’ had actually been coined two decades earlier by the English scientist Robert Hooke. In 1655, he had examined plant tissue and noticed dead compartments stacked together. However, neither he nor van Leeuwenhoek realised that cells are the Lego bricks of life. But that is what they are. A cell is the ‘biological atom’. There is no life – as far as we know – .

The first evidence of cells comes from fossils about 3.5 billion years old. But there is more tentative evidence, from about 3.8 billion years ago, in the shape of telltale chemical imbalances in rocks that are characteristic of living things. The first cells, known as prokaryotes, were essentially just tiny transparent bags of gloop less than a thousandth of a millimetre across. The bag, by concentrating stuff inside, speeded up key chemical reactions such as those that generate energy. It also protected proteins and other fragile products of those reactions from toxic substances such as acids and salt in the environment. The bag of gloop was an island haven in an ocean of disorder and chaos, a protected micro-universe where order and complexity might safely grow.

The complexity of such cells was in large part due to the proteins – megamolecules assembled from amino-acid building blocks and made of millions of atoms. Depending on their shape and chemical properties, these Swiss-army-knife molecules can carry out a myriad tasks, from speeding up chemical reactions to acting as cellular scaffolding to flexing like coiled springs to power the movement of cells. Even a simple bacterium possesses about four thousand different proteins, though some proteins, such as those needed for reproduction, are assembled, or expressed, only intermittently. The structure of these proteins is encoded by deoxyribonucleic acid, or DNA, a double-helical molecule floating freely as a loop in the chemical soup, or cytoplasm, inside a cell.

Cellular structure is beautifully intricate. First, there is the bag, or membrane. This is made of fatty acids, molecules that are characterised by having a water-loving end and a water-hating end. When such lipids come together in large numbers – typically a billion – they spontaneously self-assemble into two layers, with their water-hating ends on the interior and their water-loving ends on the outside.

The lipid layers that enclose a cell are not a passive barrier. Far from it. This double skin regulates the molecules coming in and going out of the cell. Imagine the cell as an ancient city surrounded by a wall. In the same way that small creatures such as mice can pass easily back and forth through the city wall, small molecules can pass unhindered in and out of the cell membrane. And, just as bigger creatures such as people are admitted only through gates in a city wall, the passage of big molecules is regulated by ‘gates’ in the cell membrane. For instance, there are proteins shaped like hollow tubes spanning the width of the membrane through which bigger molecules can tunnel into and tunnel out of the cell. And there are transporter proteins whose job is to shuttle bigger molecules physically from one side of the membrane to the other.

The molecules that come in to the cell are those needed for energy and to make proteins and to provide information about the outside world. For instance, an abundance in the surrounding environment of molecules necessary for building new cells might trigger a cell to reproduce.3 On the other hand, a shortage of water molecules coming across the membrane might warn a cell that it is in danger of drying out. This might trigger a cascade of chemical reactions inside the cell, ultimately causing a stretch of DNA to be copied repeatedly into molecules called ribonucleic acid, or RNA. These find their way to ribosomes, nanomachines that use the RNA templates to make proteins that might be components of a mucus that will protect the cell from dehydration.4 Too big to pass through the cell membrane, the proteins flooding out through the cytoplasm in their millions are packaged into membrane sacs, or vesicles, which fuse with the cell membrane. The membrane can then open up, without rupturing and losing its structural integrity, and cast them into the outside world.

But cells, in addition responding to molecules in their environment, also respond to molecules from . Even the simplest and most ancient prokaryotes cooperated with each other, which is revealed by fossils of large microbial communities known as stromatolites. Living stromatolites can still be found today – for instance, in shallow tropical waters off the western coast of Australia – but the oldest of these fossil communities is about 3.5 billion years old.

At the same time that a cell makes proteins to protect itself from environmental changes, it might produce proteins that warn others of its kind to do the same. Such chemical signalling is crucial to the survival of simple prokaryotes, which often live in huge colonies known as biofilms, quite possibly the first organised structures to appear on Earth. The cells on the inside of such a biofilm might secrete a sugary protein that sticks their membranes to the membrane of other cells, whereas those on the outside of the film might produce proteins that help protect them from environmental toxins. Some cells will even kill themselves in order to yield up precious nitrogen for the good of their companions. This kind of cooperation, with cells within a group differentiating to carry out different tasks, is reminiscent of the cells in our bodies. It hints at how such cellular super-cooperation might have got started billions of years ago.

There are limits on the size and complexity of prokaryotes. For one thing, the proteins assembled, or expressed, by their DNA can travel only by drifting slowly, or diffusing, across a cell. Beyond a certain size, a prokaryote is therefore suicidally slow in reacting to environmental dangers. This problem has been solved by rare prokaryotes such as , discovered only in 1997. The giant sulphur bacterium, which is about 0.75 millimetres across and easily visible to the naked eye, possesses not one loop of DNA but , spread evenly throughout its cytoplasm. This means that proteins expressed by local strands of DNA, even if they diffuse slowly, can still get to all parts of the cell rapidly.

But there is another serious problem that keeps prokaryotes small. The bigger one of them grows the more energy it needs. If it were to use the strategy of , however, an increasing proportion of that energy would be needed for manipulating large quantities of DNA. Since this would be at the expense of any other cellular processes, the road to increased complexity is well and truly blocked.

But there is another way to grow big: take up cannibalism.

About 1.8 billion years ago, a prokaryote swallowed another prokaryote. Prokaryotes actually include bacteria and more exotic archaea bacteria, microorganisms that survive in extreme environments such as boiling sulphur springs and so were probably among the first life forms on Earth.5 What actually happened 1.8 billion years ago was that an .

Such an event must have occurred innumerable times before. But, in all cases, the bacterium was either devoured or spat out. This time, for some unknown reason, the bacterium survived. More than that. . There was some mutual benefit for the swallower and swallowee. The latter found a protective environment, safe from the hostile outside world, and the former a new power source.

The evidence that something like this did indeed happen was gathered by the American biologist Lynn Margulis (the first...