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Thanks to Anne Thomas and Pat Monaghan

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A. OK...Pick an organism. Plant, animal... whatever. Put your choice face down on the table.Watch carefully...

Whatever you picked, it's made from a huge numberof smaller bits, called CELLS. (About fifty thousand billion of them in a human).

B. CELLS are staggeringly complex biological structures but to hell with that. Let's just say they're tiny, bubble-like sacks containing lots of 'special' chemicals called PROTEINS. simp 10x final

PROTEINS are amazing things... they manipulate other chemicals. And the correct 'cocktail' of different PROTEINS will herd, alter and combine other 'biological' chemicals into fully-functioning CELLS.2

C. OK... here's the really crucial bit... Depending on exactly which PROTEINS3 you set loose, you don't just get any old CELL... you get a specific type of CELL that belongs to a specific organism and no other, be it a WHALE or a WOMBAT, a WATERMELON or a WHELK.

So - the next step is to select and assemble the right PROTEINS. This is where the infamous DNA4 comes into the trick. It selects PROTEINS.

DNA is a long chemical strand twisted into a famous shape: the DOUBLE HELIX . The DNA gets coiled up over and over again into shapes called CHROMOSOMES and kept inside the core or NUCLEUS of the CELL.

D. [image, unknown] The DNA STRAND contains a message, just like a length of cassette tape. And that message is a simple one. It's a massive list of PROTEINS.

Not particularly exciting, but the key to all life, nonetheless.


E. A copy of the DNA STRAND then leaves the NUCLEUS and enters the surrounding CELL where it meets...a RIBOSOME.5

A RIBOSOME is a DNA-reading-PROTEIN- making gizmo. It slides along the copy of the DNA, reads the list of PROTEINS and then makes these out of the CELL'S reservoir of chemicals.

F. The specific number and type of PROTEINS come sliding out of the RIBOSOME where they get set loose to do their weird manipulations, finally forming a specific type of CELL, belonging to...

One last amazing thought - the same DNA CODE resides in every single CELL of an organism. In other words, the entire set of genetic instructions for building a gerbil can be found in its tongue, eyeball or bladder. Weird, isn't it?


simp box 2 A GENE is a very short length of the whole DNA chain... just enough to say: 'Make this protein rather than that protein. Just this one - OK?'

Sounds trivial but the gene is actually a big cheese because changing the list of proteins can mean you end up with a whale instead of a watermelon.

Change it even a little bit and you create the variations between individual whales or individual watermelons. Because the DNA chain is so long, a huge number of genetic variations are possible.

The ones that are handed on from parents to their offspring are known as HEREDITARY GENES.

Add all the genes together and you have the GENETIC CODE for that particular whale or watermelon... the unique set of instructions that make it what it is.


1 In other words don't try impressing any biochemists by quoting it at them... your bluff will be called.

2 But... you can't just pour proteins and other chemicals into a bucket and produce a cell. It's more that existing cells use these mechanisms to make new ones.

3 There are thousands of different proteins.

4 Deoxyribonucleic Acid. Not that this makes us any the wiser...

5 A Ribosome is mostly made of protein, so the instructions for building it are contained in the DNA it reads. Chicken-and-egg or what?

Comments? Questions? Drop us a line...

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New Internationalist issue 293 magazine cover This article is from the August 1997 issue of New Internationalist.
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