y space between the two called the cytoplasm。 themembrane is not； as most of us imagine it； a durable； rubbery casing； something that youwould need a sharp pin to prick。 rather； it is made up of a type of fatty material known as alipid； which has the approximate consistency 鈥渙f a light grade of machine oil；鈥潯o quotesherwin b。 nuland。 if that seems surprisingly insubstantial； bear in mind that at themicroscopic level things behave differently。 to anything on a molecular scale water beesa kind of heavy…duty gel； and a lipid is like iron。
if you could visit a cell； you wouldn鈥檛 like it。 blown up to a scale at which atoms wereabout the size of peas； a cell itself would be a sphere roughly half a mile across； and supportedby a plex framework of girders called the cytoskeleton。 within it； millions upon millionsof objects鈥攕ome the size of basketballs； others the size of cars鈥攚ould whiz about likebullets。 there wouldn鈥檛 be a place you could stand without being pummeled and rippedthousands of times every second from every direction。 even for its full…time occupants theinside of a cell is a hazardous place。 each strand of dna is on average attacked or damagedonce every 8。4 seconds鈥攖en thousand times in a day鈥攂y chemicals and other agents thatwhack into or carelessly slice through it； and each of these wounds must be swiftly stitched upif the cell is not to perish。
the proteins are especially lively； spinning； pulsating； and flying into each other up to abillion times a second。 enzymes； themselves a type of protein； dash everywhere； performingup to a thousand tasks a second。 like greatly speeded up worker ants； they busily build and rebuild molecules； hauling a piece off this one； adding a piece to that one。 some monitorpassing proteins and mark with a chemical those that are irreparably damaged or flawed。 onceso selected； the doomed proteins proceed to a structure called a proteasome； where they arestripped down and their ponents used to build new proteins。 some types of protein existfor less than half an hour； others survive for weeks。 but all lead existences that areinconceivably frenzied。 as de duve notes； 鈥渢he molecular world must necessarily remainentirely beyond the powers of our imagination owing to the incredible speed with whichthings happen in it。鈥�
but slow things down； to a speed at which the interactions can be observed； and thingsdon鈥檛 seem quite so unnerving。 you can see that a cell is just millions of objects鈥攍ysosomes；endosomes； ribosomes； ligands； peroxisomes； proteins of every size and shape鈥攂umping 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。 鈥渢hismeans；鈥潯ays nuland； 鈥渢hat 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。鈥�
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鈥攖hat鈥檚 enough to fill four olympic…sized swimming pools鈥攖o keep all those cells freshly oxygenated。 （and that鈥檚 at rest。 duringexercise the rate can increase as much as sixfold。） the oxygen is taken up by themitochondria。 these are the cells鈥櫋ower 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鈥檚 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鈥檚processes； 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鈥檚 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鈥攆or instance； when infected鈥攂ut mostly they die because they are told to。
indeed； if not told to live鈥攊f not given some kind of active instruction from another cell鈥攃ells 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鈥攁 cacophony of messages鈥攆rom 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鈥攐r； 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鈥檚 because of a curious； determined； barely understood molecule that is itself notalive and for the most part doesn鈥檛 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 鈥渢he single best idea that anyone has ever had鈥濃�攁nd then； for reasons that take a littleexplaining； locked it away in a drawer for the next fifteen years。
w锛穡锛巟i锛sh锛祇txt。c锛痬
25 DARWIN鈥橲 SINGULAR NOTION
t！xt…澶╁爞
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。 鈥渆veryone is interested in pigeons；鈥潯e observedhelpfully。
elwin鈥檚 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 scarcely out of controversy； in all the time since鈥攏ot bad going for a man whose principal other interest was earthworms and who； but for asingle impetuous decision to sail around the world； would very probably have passed his lifeas an anonymous country parson known for； well； for an interest in earthworms。
charles robert darwin was born on february 12； 1809；1in shrewsbury； a sedate markettown in the west midlands of england。 his father was a prosperous and well…regardedphysician。 his mother； who died when charles was only eight； was the daughter of josiahwedgwood； of pottery fame。
darwin enjoyed every advantage of upbringing； but continually pained his widowed fatherwith his lackluster academic performance。 鈥測ou care