The Incredible Cell
A LOOK INSIDE
DID YOUR 100,000,000,000,000 JUST HAPPEN?
When the theory of evolution was proposed in Charles Darwin’s day, scientists had no idea of the fantastic complexity that would be discovered in the cell. Most of the parts of an average cell can be clearly seen only with powerful electron microscopes. Here are a few of the parts of a typical animal cell—all packed into a container only 1/1000th of an inch (.0025 cm) across:
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MITOCHONDRIA—These little sausages are production centers for a special molecule called ATP. The cell uses ATP molecules for energy. Inside the complex membranes of the mitochondria, ATP production may proceed at a furious rate. Over a dozen distinct chemical reactions are needed to make each ATP molecule, and all your cells together make many trillions of them every second.
RIBOSOMES—These tiny particles can barely be seen, even by powerful electron microscopes, and most of your cells contain thousands of them. Ribosomes read instructions from other molecules and build proteins your body needs, doing so to precise specifications. Ribosomes are very complex, being made of no less than 55 separate protein molecules.
MICROTUBULES—Cells can change shape by constructing or dissolving these structural elements, giving the cells a flexible “skeleton.” In very long nerve cells, microtubules form an internal “rapid transit” system.
LYSOSOMES—As little sacs containing enzymes that can destroy the cell, these serve as the cell’s stomach, breaking down substances for the cell’s use. White blood cells attack harmful bacteria with the enzymes in their lysosomes.
ENDOPLASMIC RETICULUM—This seems to serve as a cellular warehouse of proteins and other molecules, which are stored separately for later use in the cell or shipment to the outside.
GOLGI APPARATUS—It seems to help package newly synthesized protein from the endoplasmic reticulum so that the cell can use it.
NUCLEAR ENVELOPE—To protect the cell’s DNA, the nuclear envelope is made of two membranes, containing pores that are not mere holes, but complex gates, sometimes open, sometimes not.
CHROMOSOMES—Located inside the nucleus, they contain the cell’s DNA, its genetic master plan. The DNA is packaged around special proteins called histones, which may help regulate it.
CENTRIOLES—These cylinders are made of nine sets of three microtubules each. When cells divide, centrioles apparently control the tiny fibers that separate the chromosomes from each other so that each new cell gets the right genetic information.
CELL MEMBRANE—More than just a wall, the membrane must control what goes into the cell and what comes out of it. Too much fluid could rupture the cell, while not enough fluid would shut down the cell’s chemical reactions. Food must be carefully screened for dangerous substances and is admitted to the cell only after being safely wrapped up in a bit of the membrane for transport to a waiting lysosome.
Of course, the above listing merely scratches the surface. A single cell is vastly more complex than anything man has ever made. Really, could it have happened by chance?