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edible speed with whichthings happen in it。”
but slow things down； to a speed at which the interactions can be observed； and thingsdon’t seem quite so unnerving。 you can see that a cell is just millions of objects—lysosomes；endosomes； ribosomes； ligands； peroxisomes； proteins of every size and shape—bumping intomillions of other objects and performing mundane tasks： extracting energy from nutrients；assembling structures； getting rid of waste； warding off intruders； sending and receivingmessages； making repairs。 typically a cell will contain some 20；000 different types of protein；and of these about 2；000 types will each be represented by at least 50；000 molecules。 “thismeans；” says nuland； “that even if we count only those molecules present in amounts of morethan 50；000 each； the total is still a very minimum of 100 million protein molecules in eachcell。 such a staggering figure gives some idea of the swarming immensity of biochemicalactivity within us。”
it is all an immensely demanding process。 your heart must pump 75 gallons of blood anhour； 1；800 gallons every day； 657；000 gallons in a year—that’s enough to fill four olympic…sized swimming pools—to keep all those cells freshly oxygenated。 （and that’s at rest。 duringexercise the rate can increase as much as sixfold。） the oxygen is taken up by themitochondria。 these are the cells’ power stations； and there are about a thousand of them in atypical cell； though the number varies considerably depending on what a cell does and howmuch energy it requires。
you may recall from an earlier chapter that the mitochondria are thought to have originatedas captive bacteria and that they now live essentially as lodgers in our cells； preserving theirown genetic instructions； dividing to their own timetable； speaking their own language。 youmay also recall that we are at the mercy of their goodwill。 here’s why。 virtually all the foodand oxygen you take into your body are delivered； after processing； to the mitochondria；where they are converted into a molecule called adenosine triphosphate； or atp。
you may not have heard of atp； but it is what keeps you going。 atp molecules areessentially little battery packs that move through the cell providing energy for all the cell’sprocesses； and you get through a lot of it。 at any given moment； a typical cell in your bodywill have about one billion atp molecules in it； and in two minutes every one of them willhave been drained dry and another billion will have taken their place。 every day you produceand use up a volume of atp equivalent to about half your body weight。 feel the warmth ofyour skin。 that’s your atp at work。
when cells are no longer needed； they die with what can only be called great dignity。 theytake down all the struts and buttresses that hold them together and quietly devour theirponent parts。 the process is known as apoptosis or programmed cell death。 every daybillions of your cells die for your benefit and billions of others clean up the mess。 cells canalso die violently—for instance； when infected—but mostly they die because they are told to。
indeed； if not told to live—if not given some kind of active instruction from another cell—cells automatically kill themselves。 cells need a lot of reassurance。
when； as occasionally happens； a cell fails to expire in the prescribed manner； but ratherbegins to divide and proliferate wildly； we call the result cancer。 cancer cells are really justconfused cells。 cells make this mistake fairly regularly； but the body has elaboratemechanisms for dealing with it。 it is only very rarely that the process spirals out of control。 onaverage； humans suffer one fatal malignancy for each 100 million billion cell divisions。
cancer is bad luck in every possible sense of the term。
the wonder of cells is not that things occasionally go wrong； but that they manageeverything so smoothly for decades at a stretch。 they do so by constantly sending andmonitoring streams of messages—a cacophony of messages—from all around the body：
instructions； queries； corrections； requests for assistance； updates； notices to divide or expire。
most of these signals arrive by means of couriers called hormones； chemical entities such asinsulin； adrenaline； estrogen； and testosterone that convey information from remote outpostslike the thyroid and endocrine glands。 still other messages arrive by telegraph from the brainor from regional centers in a process called paracrine signaling。 finally； cells municatedirectly with their neighbors to make sure their actions are coordinated。
what is perhaps most remarkable is that it is all just random frantic action； a sequence ofendless encounters directed by nothing more than elemental rules of attraction and repulsion。
there is clearly no thinking presence behind any of the actions of the cells。 it all just happens；smoothly and repeatedly and so reliably that seldom are we even conscious of it； yet somehowall this produces not just order within the cell but a perfect harmony right across the organism。
in ways that we have barely begun to understand； trillions upon trillions of reflexive chemicalreactions add up to a mobile； thinking； decision…making you—or； e to that； a rather lessreflective but still incredibly organized dung beetle。 every living thing； never forget； is awonder of atomic engineering。
indeed； some organisms that we think of as primitive enjoy a level of cellular organizationthat makes our own look carelessly pedestrian。 disassemble the cells of a sponge （by passingthem through a sieve； for instance）； then dump them into a solution； and they will find theirway back together and build themselves into a sponge again。 you can do this to them overand over； and they will doggedly reassemble because； like you and me and every other livingthing； they have one overwhelming impulse： to continue to be。
and that’s because of a curious； determined； barely understood molecule that is itself notalive and for the most part doesn’t do anything at all。 we call it dna； and to begin tounderstand its supreme importance to science and to us we need to go back 160 years or so tovictorian england and to the moment when the naturalist charles darwin had what has beencalled “the single best idea that anyone has ever had”—and then； for reasons that take a littleexplaining； locked it away in a drawer for the next fifteen years。
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25DARWIN’S SINGULAR NOTION
小x说s网
in the late summer or early autumn of 1859； whitwell elwin； editor of the respectedbritish journal the quarterly review； was sent an advance copy of a new book by thenaturalist charles darwin。 elwin read the book with interest and agreed that it had merit； butfeared that the subject matter was too narrow to attract a wide audience。 he urged darwin towrite a book about pigeons instead。 “everyone is interested in pigeons；” he observedhelpfully。
elwin’s sage advice was ignored； and on the origin of species by means of naturalselection； or the preservation of favoured races in the struggle for life was published in latenovember 1859； priced at fifteen shillings。 the first edition of 1；250 copies sold out on thefirst day。 it has never been out of print； and scar