Gödel, Escher, Bach An Eternal Golden Braid by Douglas R. Hofstadter

So in our case, we have an enzyme which likes the letter C. If, in folding up,

an enzyme happens to cross itself. that's okay-just think of it as going

under or over itself. Notice that all its amino acids playa role in the

determination of an enzyme's tertiary structure.

Punctuation, Genes, and Ribosomes

Now one thing remains to be explamed. Why is there a blank in box AA of

the Typogenetic Code? The answer is that the duplet AA acts as a punctua-

tion mark inside a strand, and it signals the end of the code for an enzyme.

That is to say, one strand may code for two or more enzymes if it has one or

more duplets AA in it. For example, the strand

codes for two enzymes:

CG GA TA CT AA AC CG A

cop -ina -rpy -off

and

cut.--cop

with the AA serving to divide the strand up into two "genes". The definition

of gene is: that portion of a strand which codes for a single emyme. Note that the

mere presence of AA inside a strand does not mean that the strand codes

for two enzymes. For instance, CAAG codes for "mvr -del". The AA begins

on an even-numbered unit and therefore is not read as a duplet!

The mechanism which reads strands and produces the enzymes which

are coded inside them is called a ribosome. (In Typogenetics, the player of

the game does the work of the ribosomes.) Ribosomes are not in any way

responsible for the tertiary structure of enzymes, for that is entirely deter-

mined once the primary structure is created. Incidentally, the process of

translation always goes from strands to em.ymes, and never in the reverse

direction.

Puzzle: A Typogenetical Self-Rep

Now that the rules of Typogenetics have been fully set out, you may find it

interesting to experiment with the game. In particular, it would be most

interesting to devise a self-replicating strand. This would mean something

along the following lines. A single strand is written down. A ribosome acts

on it, to produce any or all of the enzymes which are coded for in the

strand. Then those enzymes are brought into contact with the original

strand, and allowed to work on it. This yields a set of "daughter strands".

The daughter strands themselves pass through the ribosomes, to yield a

second generation of enzymes, which act on the daughter strands; and the

512 Self-Ref and Self-Rep