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

This is accomplished by having the reading frames of the two genes shifted

relative to each other, by exactly one unit. The density of information-

packing in such a scheme is incredible. This is, of course, the inspiration

behind the strange "5/17 haiku" in Achilles' fortune cookie, in the Canon by

Intervallic Augmentation.

Recap

In brief, then, this picture emerges: from its central throne, DNA sends off

long strands of messenger RNA to the ribosomes in the cytoplasm; and the

ribosomes, making use of the "flashcards" of tRNA hovering about them,

efficiently construct proteins, amino acid by amino acid, according to the

blueprint contained in the mRNA. Only the primary structure of the

proteins is dictated by the DNA; but this is enough, for as they emerge

from the ribosomes, the proteins "magically" fold up into complex confor-

mations which then have the ability to act as powerful chemical machines.

Levels of Structure and Meaning in Proteins and Music

We have been using this image of ribosome as tape recorder, mRNA as
tape, and protein as music. It may seem arbitrary, and yet there are some
beautiful parallels. Music is not a mere linear sequence of notes. Our minds
perceive pieces of music on a level far higher than that. We chunk notes
into phrases, phrases into melodies, melodies into movements, and move-
ments into full pieces. Similarly, proteins only make sense when they act as
chunked units. Although a primary structure carries all the information for
the tertiary structure to be created, it still "feels" like less, for its potential is
only realized when the tertiary structure is actually physically created.
Incidentally, we have been referring only to primary and tertiary
structures, and you may well wonder whatever happened to the secondary
structure. Indeed, it exists, as does a quaternary structure, as well. The
folding-up of a protein occurs at more than one level. Specifically, at some
points along the chain of amino acids, there may be a tendency to form a
kind of helix, called the alpha helix (not to be confused with the DNA double
helix). This helical twisting of a protein is on a lower level than its tertiary
structure. This level of structure is visible in Figure 95. Quaternary struc-
ture can be directly compared with the building of a musical piece out of
independent movements, for it involves the assembly of several distinct
polypeptides, already in their full-blown tertiary beauty, into a larger
structure. The binding of these independent chains is usually accomplished
by hydrogen bonds, rather than covalent bonds; this is of course just as with
pieces of music composed of several movements, which are far less tightly
bound to each other than they are internally, but which nevertheless form a
tight "organic" whole.
The four levels of primary, secondary, tertiary, and quaternary struc-
ture can also be compared to the four levels of the MU-picture (Fig. 60) in

Self-Ref and Self-Rep 525