eemed with life in ways and numbers that no one had previously suspected。
inspired by leeuwenhoek’s fantastic findings； others began to peer into microscopes withsuch keenness that they sometimes found things that weren’t in fact there。 one respecteddutch observer； nicolaus hartsoecker； was convinced he saw “tiny preformed men” in spermcells。 he called the little beings “homunculi” and for some time many people believed that allhumans—indeed； all creatures—were simply vastly inflated versions of tiny but pleteprecursor beings。 leeuwenhoek himself occasionally got carried away with his enthusiasms。
in one of his least successful experiments he tried to study the explosive properties ofgunpowder by observing a small blast at close range； he nearly blinded himself in the process。
2leeuwenhoek was close friends with another delft notable； the artist jan vermeer。 in the mid…1660s； vermeer；who previously had been a petent but not outstanding artist； suddenly developed the mastery of light andperspective for which he has been celebrated ever since。 though it has never been proved； it has long beensuspected that he used a camera obscura； a device for projecting images onto a flat surface through a lens。 nosuch device was listed among vermeers personal effects after his death； but it happens that the executor ofvermeers estate was none other than antoni van leeuwenhoek； the most secretive lens…maker of his day。
in 1683 leeuwenhoek discovered bacteria； but that was about as far as progress could getfor the next century and a half because of the limitations of microscope technology。 not until1831 would anyone first see the nucleus of a cell—it was found by the scottish botanistrobert brown； that frequent but always shadowy visitor to the history of science。 brown； wholived from 1773 to 1858； called it nucleus from the latin nucula； meaning little nut or kernel。
not until 1839； however； did anyone realize that all living matter is cellular。 it was theodorschwann； a german； who had this insight； and it was not only paratively late； as scientificinsights go； but not widely embraced at first。 it wasn’t until the 1860s； and some landmarkwork by louis pasteur in france； that it was shown conclusively that life cannot arisespontaneously but must e from preexisting cells。 the belief became known as the “celltheory；” and it is the basis of all modern biology。
the cell has been pared to many things； from “a plex chemical refinery” （by thephysicist james trefil） to “a vast； teeming metropolis” （the biochemist guy brown）。 a cell isboth of those things and neither。 it is like a refinery in that it is devoted to chemical activityon a grand scale； and like a metropolis in that it is crowded and busy and filled withinteractions that seem confused and random but clearly have some system to them。 but it is amuch more nightmarish place than any city or factory that you have ever seen。 to begin withthere is no up or down inside the cell （gravity doesn’t meaningfully apply at the cellularscale）； and not an atom’s width of space is unused。 there is activity every where and aceaseless thrum of electrical energy。 you may not feel terribly electrical； but you are。 thefood we eat and the oxygen we breathe are bined in the cells into electricity。 the reasonwe don’t give each other massive shocks or scorch the sofa when we sit is that it is allhappening on a tiny scale： a mere 0。1 volts traveling distances measured in nanometers。
however； scale that up and it would translate as a jolt of twenty million volts per meter； aboutthe same as the charge carried by the main body of a thunderstorm。
whatever their size or shape； nearly all your cells are built to fundamentally the same plan：
they have an outer casing or membrane； a nucleus wherein resides the necessary geneticinformation to keep you going； and a busy 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 “of a light grade of machine oil；” to 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’t 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—some the size of basketballs； others the size of cars—would whiz about likebullets。 there wouldn’t 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—ten thousand times in a day—by 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； “the molecular world must necessarily remainentirely beyond the powers of our imagination owing to the incredible 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 k