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

new strands which will dictate further enzymes, etc. etc.! This is mixing

levels with a vengeance! Think, for the sake of comparison, how different

the MU-puzzle would have been if each new theorem produced could have

been turned into a new rule of inference by means of some code.

How is this "translation" done? It involves a Typogenetic Code by which

adjacent pairs of bases-called "duplets"-in a single strand represent

different amino acids. There are sixteen possible duplets: AA, AC, AG, AT,

CA, CC, etc. And there are fifteen amino acids. The Typogenetic Code is

shown in Figure 87.

Second Base

A C G

A cut del

s

C mvr mvl cop

s s

G Ina mc mg

s r

T rpy rpu lpy

r I

T

SWI

s

off

r

int

r

lpu

I

r

I

I

I

FIGURE 87. The Typogenetic Code, by

which each duplet in a strand codes for one

of fifteen "amino acids" (or a punctuation

mark).

According to the table, the translation of the duplet GC is "inc" ("insert a

C"); that of AT is "swi" ("switch strands"); and so on. Therefore it becomes

clear that a strand can dictate an enzyme very straightforwardly. For

example, the strand

TAGATCCAGTCCACATCGA

breaks up into d uplets as follows:

TA GA TC CA GT CC AC AT CG A

with the A left over at the end. Its translation into an enzyme is:

rpy -ina -rpu -mvr - int - mvl-cut - swi -cop.

(Note that the leftover A contributes nothing.)

Tertiary Structure of Enzymes

What about the little letters's', 'I', and 'r' in the lower righthand corner of

each box? They are crucial in determining the enzyme's binding-prefer-

ence, and in a peculiar way. In order to figure out what letter an enzyme

likes to bind to, you have to figure out the enzyme's "tertiary structure",

which is itself determined by the enzyme's "primary structure". By its

(^510) Self-Ref and Self-Rep